Signs of Summer 10: West Toward Home (Part 1)!

Walking on a Pennsylvania trail. Photo by D. Sillman

(Click here to listen to a audio version of this blog!)

We left Apollo in the early afternoon and drove west in bright sunshine. The air was as warm and humid as you would expect for Western Pennsylvania in late July. It had rained overnight, but all of the pavement and any lingering puddles had thoroughly dried. In a few hours the sun dropped low enough in the sky to glare up the windshield and our sunglasses. We had to flip down the sun visors and watch the road ahead of us through a narrow, horizontal slit between the visor’s edge and the dashboard. Driving west in the late afternoon is tough.

The topography of Western Pennsylvania is rolling and curvy. Long ridges run, in general from the SW to the NE reflecting the pattern of the nearby Chestnut Ridge and Laurel Hill. This is the western edge of the Allegheny Mountains which in turn is the western section of the Appalachian Mountain Range. The Appalachians are ancient mountains, hundreds of millions of years old. They are well worn and fragmented by weathering and erosion. In between the ridges are rills, and creeks and rivers of varying sizes and energies. The flowing water adds more complexity to the landscape. It has been said that here in Western Pennsylvania there are no hills, only valleys!

You feel this topography when you drive on all of the area roads. There are almost no straight lines from any point A to any point B. Short, straight line map distances often require long arcs and, sometimes, opposite directional hypotenuses to be accomplished. It took us 45 minutes of zigging and zagging to get to the Turnpike entrance and really start our journey west!

The Kiski River and surrounding ridges. Photo by D. Sillman

All of the ridges and valleys here are lush and green and well covered with trees. This was the middle of the great eastern hardwood forest of pre-colonial North America. Most of those trees (the oaks, the chestnuts, the sugar maples, the white pines and, further north and down in many nearby, cool valleys, the hemlocks) were clear cut in the late 19th and early 20th Centuries, or, in the case of the chestnuts, killed by an invasive fungus. They were replaced so rapidly and so efficiently by a hodgepodge of hardy, fast growing hardwood species (like red maple, white ash and black cherry) that it looks like the great eastern forest is still here. The diversity and array of trees we see today, though, are the product of human interference. These forests have never existed on Earth before! Their persistence and sustainability are not known.

The altitude of Pittsburgh is expressed in most references as a broad range. The city, and much of Western Pennsylvania, is between 710 and 1370 feet above sea level. This range, of course, reflects the topographic complexity of the ridge and valley terrain. So many interesting microclimates and microhabitats are generated here! So many wonderful places to hike and explore!

Photo by D. Sillman

Driving west we get to Ohio in about an hour. The eastern-most parts of Ohio look like Western Pennsylvania: rolling, stream bisected, often forested terrain, but soon we drive out of the ridge and valley topography into at first a rolling and then an increasingly flattened plane. Looking at a road map (which is a rare thing, I know, in these days of I-Phones and audio-based direction systems, but I don’t feel right unless I have my Rand McNally road atlas with me in the car!) you see the sudden change in the nature of the surrounding highway grid. Interstates and local roads run increasingly due north and south or due east and west making a neat, endlessly repeating geometric pattern of squares and rectangles.

Ohio was also part of the pre-colonization hardwood forest. One of my agronomy professors at Ohio State talked about the cutting and clearing of all of trees to make space for agricultural fields. There were so many trees felled that the downed wood could not be used! It was, instead, just burned in place. Great piles of trunks and branch wood were set on fire generating mountains and mountains of ash. The ash eventually washed into the surrounding creeks and rivers turning the water gray. Surface water pollution in the United States has a very long history!

Photo by D. Sillman

Looking out the window of the car as we race across the geometric grid of Ohio we see occasional stands of trees (the same fast growing species that dominated Western Pennsylvania), but mostly we see open fields in which hay has been recently cut and baled or in which dense stands of corn or soybeans are planted. The great Ohio forest has become open farmland.

We are going steadily up. The altitude of Columbus, Ohio is 902 feet above sea level. The precision of a single number for this average altitude reflects the leveling of the topographic landscape. There are hills, but they are low and rolling.

Photo by D. Sillman

The next state is Indiana. The square, north-south and east-west grid of roads continues. Indiana was the western edge of the pre-colonization, eastern hardwood forest. It was also vigorously cleared for agriculture. Expansive fields of corn, soybeans, and hay dominate the roadsides. Indianapolis sits at 900 feet above sea level, almost the same altitude as Columbus, so we have been driving along a steady, flat plane.

Water towers have become more and more prominent across the landscape. Each is labeled with the name of their town. You see the scattered pattern of towns stretching out toward the increasingly horizontal horizon line. The towers are a symptom of the flatness of the terrain. They enable municipal water systems to pump water into their elevated tanks and then use gravity (free energy!!) to maintain delivery pressure in the water mains. Back in Pennsylvania there were more water tanks than towers. The tanks were located on high hills in the middle of water-main grids. There was a tank very close to my old house in Apollo that was filled by pumped water from the pressurized water mains.

The rest stops in Indiana are densely wooded and shady. The trees are different that the fast growing array we had seen in Pennsylvania and Ohio. Chestnut oaks, northern red oaks and basswood trees dominate the “rest stop forests.” The wind was also much more intense. It blew hard and consistently all across Indiana, Illinois, Iowa and beyond! I remember being out on my Uncle Harold’s farm in northwest Iowa in late May twenty years ago, seeing extensive fields of three inch tall corn all of which were laying down across the soil surface because of the wind. I didn’t remember the wind from my childhood visits to Iowa, but was assured by my cousins that the wind always blew in Iowa.

We are driving out from under the extensive cloud cover that is generated at least in part by the proximity of the Great Lakes. Pittsburgh is one of the least sunny cities in the United States. It has, on average, only 59 clear days a year and 103 partly cloudy days (so, 162 “sunny days”). Pittsburgh has 203 days that are densely cloudy! On average, cities in the United States have 205 “sunny days,” and northern Colorado (our destination”) has 244 “sunny days” each year.  Pittsburgh gets 38 inches of rain each year while Columbus gets 56 inches and Indianapolis, 42 inches. Our destination in northern Colorado gets 14 inches of rain each year. We are driving from the cloudy, wet forests of the east to the sunny, dry grasslands and mountains of Colorado.

On to Illinois, Iowa, Nebraska and Colorado!

(More next week!)

 

Posted in Bill's Notes | Leave a comment

Signs of Summer 9: Sit Spots

Photo by h.hach, Pixabay

(Click here to listen to an audio version of this blog!)

(Much of this blog was originally published in July, 2013)

When you are looking at Nature you see and experience its details inversely proportionally to the speed at which you are moving.  From my car as I drive along roads that wind through the woods I see much less than if I were riding my bike on that road or, better yet, on a trail that cuts through those surrounding  woods. And, if I were walking along that trail I would see a great deal more than I would have from my bike. It is logical, then, that if I were sitting absolutely still, letting all of the events of the trail move past me instead of vice-versa, I would see even more.

Robin fledgling. Photo by D. Sillman

Jon Young in his book “What the Robin Knows” (2012, Houghton Mifflin) has a whole chapter dedicated to zero velocity observations. He emphasizes the importance of finding a place in which you can, in a non-locomotory way, dig deeply into the details of an ecosystem. Your “sit spot,” according to Young, is a place that is easy to reach, a place where you feel at peace and safe, a place that you get to know very well.

Young puts learning about Nature via these sit spots into a much broader context: he presents it as a model for how all educational endeavors should be structured. For profound, “deep” learning to occur, according to Young, a student must make visceral connections between themselves and the subject. They must make their own observations of their subject and slowly put these observations together into a pattern. A student accomplishing this “owns” their education, and the subject they are studying becomes a part of their existence.  The easiest, and least effective, way to teach, as those of us who teach know far too well, is to stand in front of your students and point everything out. Delineating these long lists feels efficient but it denies the students the opportunity to make their connections with the subject. Facilitating this connection is really the job of a teacher because once that is accomplished, learning is sure to follow.

Photo by D. Sillman

The sit spot is the place where a deep, visceral connection between a student (you) and the subject (Nature) can be made. There may be a teacher involved encouraging and guiding the connections, but they must not explain too much or go too quickly. Better yet, the “teacher” may be the student’s own intellect and work ethic that helps to keep them focused and connected to the events and things going on around them.

Sit spot observations need to be recorded, organized and developed. This is a complex building process not just an experience of the moment. Keeping a notebook of your observations and taking the time to ask questions and to try to connect events and develop patterns in these at first isolated occurrences is the key to absorbing and growing with and into the subject.

Photo by D. Sillman

My sit spot is in the back room of my house. My writing desk faces a large window that looks out onto the small, enclosed space of my back yard. The back (north) side of the yard is lined with bushy crabapple trees and a handsome, nut producing, American Chestnut tree (a survivor!). The right (east) side is lined with a continuous wall of twenty foot tall arbor vitae that blend in to a stand of twenty-five year old hemlock trees. The left (west) side of the yard has two fifty year old blue spruce trees and  a broad, similarly aged red maple. Five scarlet and white oak pole trees (now fifteen to twenty feet tall) are growing under and around the spruces. The center of the yard is a fifteen by fifteen foot basketball court with a crooked pole (a tree once fell on it!) and wobbly backboard and rim. I have watched this space for years now and it has been the scene of numerous dramas and unexpected observations many of which have been subjects of past blog postings.

Photo by D. Sillman

There was last summer’s poorly placed cardinal nest and the persistence and eventual success of the crow and blue jay nest predators who nullified all of the parental cardinals’ hard work and dedication by consuming their eggs and their nestlings. There was the very recent, mid-season soap opera staring the Carolina wrens and their mating triangle. There were the deer in mid-winter walking single file through their resource space on the edge of the backyard with each trailing individual eating exactly what the lead doe ate in exactly the same order. Just a few minutes ago I watched a male robin dig a worm out from between the concrete squares of the basketball court and gobble it quickly down in spite of the angry demands of an incredible fat, female robin who must be ready to lay a large number of eggs.  There is also the carnival of the two woodchucks who use the basketball court as their starting gate as they blast under the arbor vitae and through the electric fence that my neighbor has set up to secure his garden.

Observations from my sit spot have filled a dozen notebooks. Some of these have been curious and simply entertaining while others have led to some interesting science and speculation. Science is, after all, not just observing but is a process by which you learn to ask more and more profound questions (and then figure out how you might answer them!). It is the ultimate learning experience!

I hope that my new home in Colorado has as good a view of the natural world as I have enjoyed here in Pennsylvania! More in two weeks!

 

Posted in Bill's Notes | 2 Comments

Signs of Summer 7: Ancient Ecosystems Underfoot

H. Harder, Wikimedia

(Click here to listen to an audio version of this blog!)

(Most of this blog was originally published in June 2014)

One of the Big Ideas in Biology that has grown clearer and more compelling to me over the years was very well expressed by the German biologist Ernst Haeckel back in the Nineteenth Century: “Nothing is constant but change. All existence is a perpetual flux of being and becoming.”

Organisms change, ecosystems change, climates change, genes change, proteins change: change is the common currency of an individual’s life experience and also the essence of all extended and interconnected life experiences. Back in June, 2014 my daughter Marian and her friend (now husband) Lee Drake were here for a few days on a short, summer break. Marian was on her way from Albuquerque to a month at a research station in Uganda, and Lee was taking a much needed respite from his extensive worldwide business traveling. They headed out one afternoon to go look for fossils and came back with a carload of shale from a road cut just north of Ford City.

We spread the rocks out on a table down in the basement and began to brush and clean the pieces. The fossils were stunning! I found my fossil books and we started putting names on some of the specimens. We also made inferences on the age and type of the shale layer that they were from based on the types of fossils that were present. Lee described the crunching feel of fossil-rich shale debris underfoot as they poked and explored the fresh road cut for specimens.

Pecopteris (D. Sillman)

There were three main types of fossils: a tree fern fossil called Pecopteris, a seed fern fossil called Neuropteris, and sphenopsid (“horsetail”) called Calamites. The abundance of these three plants helped us to determine that these rocks were part of the Mahoning shale layer. This shale was laid down about three hundred million years ago during the later (“Pennsylvanian”) portion of the Carboniferous Period. This site in which these shales formed was a swampy forest located on a delta plain near the coastline of one of the world’s incredibly extensive oceans (see painting above by H. Harder). Now this ecosystem and its location does seem quite a change from the present day mixed hardwood forests that dominate our landlocked Western Pennsylvania, but there were other differences that were even more overwhelming!

To begin with what we now call “Pennsylvania” was attached to a massive continental assemblage that included not only North America but also South America, Africa, Europe, Asia, Australia, Antarctica, and India. This was the giant continent called “Pangea,” and it contained all of the major land masses of the Earth! All of the rest of Earth was one, continuous ocean!

Neuropteris (D. Sillman)

Further, Pangea was located far down in the southern hemisphere! “Pennsylvania” was on its northern coast and was located very near the equator! The climate here, then, was warm and tropical and had no “sun-seasons” of summer, fall, winter, or spring. Adding to the warmth of the climate was an atmosphere enriched in carbon dioxide (40% higher carbon dioxide levels than today) which trapped heat in an exaggerated greenhouse effect. Atmospheric oxygen levels were also much higher (35% of the atmosphere was molecular oxygen compared to 20% today). So each breath of air was different! Further, we were rotated about ninety degrees away from our present orientation (so our current “west” was our ancient “north”).

The formation of Pangea came about via the collision of the many smaller continents that each moved along on their respective tectonic plates. When these continents collided they forced masses of continental materials in between them to fold upward thus making great mountain ranges. The range near “Pennsylvania” was one of the greatest lines of mountains ever formed on Earth. The present day Himalayas are thought to be similar to this ancient, amazing up-thrust of rock and crust. These mountains were/are the Appalachians which even as they were rising began to erode to form the rocks, gravels, sands, and silts than made up the soils out of which our ancient swamp forests grew. The steady flow of these eroded materials extended the ancient shoreline out into the shallow ocean and stretched and grew the swampy forests further and further away from the mountains.

Calamites (D. Sillman)

The trees of these forests were also different. There were no flowering plants on Earth and there were no deciduous trees. The trees of this ancient swampy forest were giant versions of our present day ferns and horsetails. Fifty foot tall fern trees (like Pecopteris) and one hundred foot tall horsetails (like Calamites) formed an upper canopy layer with a ground cover of other, lower growing fern and fern-like species (like Neuropteris). The warm, wet climate encouraged plant growth and the high, atmospheric carbon dioxide levels accelerated it even more. Also, the dead plants did not readily decay so the fallen branches and trunks and fronds built up in the forming soils and sediments and, eventually, in sedimentary rocks. This carbon accumulation was the source for most of our present day coal, and oil, and natural gas deposits (they were the fossils of our “fossil fuels!”). These ancient swampy forests are often referred to as “coal forests” or “coal swamps.”

And, just to complete the picture of change, the Earth three hundred million years ago was spinning faster on its axis than it does today. So a “day” was only 23 hours long!

We took some of the pieces of shale outside and laid them next to one of my red maples. I have collected Pecopteris before from some of the shale exposed on the down-slope to the west of my house, so adding these new fossils to the site seemed appropriate. We stood under the red maple tree and listened to the Carolina wrens singing and chattering up in the branches and watched two gray squirrels chase each other across the yard. Three hundred million years ago there were no birds or mammals, there weren’t even any dinosaurs (they wouldn’t be around for another seventy million years!). The only land dwelling vertebrates were early amphibians (sometimes their fossilized jaw bones are found in this shale) although the first reptiles with their revolutionary, self-contained, shelled eggs were possibly just evolving. There were terrestrial insects, though, some of which that had attained immense sizes because of the high atmospheric levels of oxygen. Dragonflies with two and a half foot wing spans, eight foot long millipedes, and three foot long scorpions flew and scuttled about in the warm, wet coal swamps.

The ancient forest would have been noisy with its giant insects and there might have even have been a scent of the ocean in the thick, warm air. Back in our present day, a thunderstorm was approaching, so we went inside. The rain fell on the fossils in the shale and began their slow erosion into soil.

“There is nothing permanent except change” (Heraclitus).

Posted in Bill's Notes | 1 Comment

Signs of Summer 6: Considering the Passenger Pigeon

Passenger pigeon. Photo by J. St.John, Wikimedia Commons

(Click here to listen to an audio version of this blog!)

The passenger pigeon (Ectopigtes migratorius) is an extinct, North American bird of great legend and mystique.  It resembled in size and markings the still living mourning dove (Zenaida macroura), and the two birds were sometimes confused for each other. The plumage of the passenger pigeon, though, was more colorful than the rather drab mourning dove. According to genetic analysis, however, the passenger pigeon was actually more closely related to birds in the genus Patagiones (a genus that includes the band-tailed pigeon (P. fasciata) and the white-crowned pigeon (P. leucocaphala)) than to birds in the genus Zenaida.

The passenger pigeon’s common name is derived from the French “passager” which means “passing by.” This very appropriate designation emphasizes the species’ tendency to be in a nearly constant state of movement across its broad, eastern and midwestern North American range. In addition to  migrating seasonally to and from the southern and Gulf Coast states, the passenger pigeon neither stayed in one particular place very long or moved about in any particularly established patterns. A specific town or section of countryside might see a swarm of passenger pigeons one year at a particular time of year and then not see them again for many years and then, often, at a completely different time of year. Their “passagers” moved about quite randomly.

The passenger pigeon’s “home range” was wherever its swarm happened to be. It is thought that there were only a very limited number of these staggeringly large flocks. As John Burroughs’ wrote in his book Birds and Poets, “the whole race (of passenger pigeons) seems to be collected in a few swarms.” Each swarm moved about on its own and was made up of hundreds of millions to billions of birds.

Passenger pigeon swarm. Illustration by F. Bond, Wikimedia Commons

The birds in a swarm flew, often at 60 miles per hour, in dense aggregations relatively close to the ground. The birds were packed so closely together that they blocked the view of the sky and the sun! A swarm could be several kilometers wide and many hundreds of kilometers long. The birds in the swarm sought out hardwood forests that were rich in “mast” (beech nuts, acorns, chestnuts, etc.). American beech trees were, according to John James Audubon, the optimal mast producers for the passenger pigeon. The small size of the beech nut made them easy to swallow and the regularity (big mast crops often every other year) and abundance of their yearly production made them an ideal food source for these birds. Possibly, the abundance of the American beech ‘s mast production was a direct, evolutionary response to counter the immense appetite of the passenger pigeons!

The passenger pigeon’s impact on the trees of North America was significant. It has been suggested that the purpose of the extremely rapid, same season germination of the white oak’s autumnally dropped acorns was to protect the acorns from inevitable spring consumption by the returning flocks of passenger pigeons. Also, the irregular masting cycle of the white oak (years of few acorns alternating with a rare, randomly occurring year of great abundance) is also thought to be a safeguard against total mast consumption by the pigeons. Further, the wide size range in northern red oak and other oak species’ acorns is thought to be an adaptation to guard against total loss of a trees’ acorns to passenger pigeons (the larger acorns could not be swallowed by the birds).

The physical impact of the passenger pigeons on the structure of their transient, forest roosting sites also affected the nature of the forests themselves. The large numbers of birds defecating for several weeks in their roosting forest killed the existing forest floor vegetation and enriched the forest soils with high levels of nutrients. The impact of the sheer weight of the roosting and nesting birds also broke limbs from the trees and added significantly to the potential fire debris on the forest floor. White oaks are more resistant to fire than most other types of oaks. They are  also more fire resistant than most of the other eastern North American tree species with which they compete. The observation that the pre-European settlement forests in eastern North America were dominated by white oaks may be at least partially attributable to the influence of the passenger pigeon not only increasing the potential for forest fires but also not being able to mass-ingest white oak acorns!

Martha, the last passenger pigeon. Photo by E. Meyer, Wikimedia Commons

The passenger pigeon has been described as a “keystone species” of our eastern forests. They increased the quality of the forest habitat and helped to create niches for a wide range of forest dwelling species. The extinction of these birds may explain some of the observed degradation and decline in the quality and productivity of these forested ecosystems and in particular may explain the diminishing abundance of white oaks throughout eastern North America.

The great fame of the passenger pigeon is primarily based on its staggeringly huge numbers. It was the most abundant bird not only in North America but possibly in the world! Its population was estimated to be 3 to 5 billion individuals in early 1800’s. This represented  25 to 40% of all of the birds in North America! Its sudden, brutally complete, human-caused extinction (the last passenger pigeon, named “Martha,” died in the Cincinnati Zoo on September 1, 1914) was both shocking and, in hindsight, inevitable.

Accounts of witnesses of the arrivals and the departures of the  swarms of passenger pigeons are the stuff of science fiction or horror novels. In an article in Audubon Magazine (2014), B. Yeoman described an account from Columbus. Ohio in 1855:

“…a growing cloud blotted out the sun as it advanced toward the city. Children screamed and ran for home. Women gathered their long skirts and hurried for the shelter of stores. Horses bolted. A few people mumbled frightened words about the approach of the millennium, and several dropped on their knees and prayed.” When the flock had passed over, two hours later, “the town looked ghostly in the now-bright sunlight that illuminated a world plated with pigeon ejecta.”

The massive swarms of the passenger pigeon and their constant migratory behavior were a very effective protection against predators. A billion birds dropping in on a forest would provide food for any number of local predators, but no wild predator could make a dent in the overall size of the population. Also, more distantly located predators could not effectively travel to and exploit the passenger pigeons because the birds, after truly wrecking up their forest habitat, quickly departed for some distant, more pristine site that was rich in mast.

There were many behavioral adaptions that allowed the passenger pigeon to live in such dense aggregations.  Some of these adaptations may also have led to the ingrained, imitation behaviors that were observed in the species. For example, for a passenger pigeon to mate or nest they had to see many other passenger pigeons mating or nesting. This dependence on large group sizes and reliance on imitation served the passenger well by stabilizing the intensely social community of the swarm, but it is also laid the seed for rapid cessation of reproduction when the massive swarms were whittled down in size by the intense human hunting of the mid and late 19th Century.

Natural predators could not locate the passenger pigeon swarm easily, and even if some distant predator did locate a swarm, they were unable to get to the birds quickly enough to prey upon it before it departed its selected forest. Humans, though, with rapid communication systems (the telegraph) and rapid transportation systems (the railroad) could locate and travel to a roosting swarm in time to wreak great damage on the pigeons. Using nets, guns, sticks and clubs human hunters took billions and billions of passenger pigeons over a few short decades and sent them in salted barrels to feed city dwellers, farm workers and livestock. It was a breath taking demonstration of human power (and ignorance) that very quickly exterminated all of the wild passenger pigeons in North America.

Recent studies have explored the history and evolution of these giant, passenger pigeon flocks. The absence of passenger pigeon bones in midden piles of ancient humans living in eastern North America coupled with precise analysis of the bird’s DNA (taken from museum specimens) have suggested that until quite recently, the passenger pigeon existed in much smaller aggregations with a much smaller overall population. Further, these populations according to genetic analysis, was subject to great extremes of growth and decline. Possibly the resurgence of the mast producing hardwood forests of North American following the last glacial maximum was the trigger that allowed the passenger pigeon’s population to surge to a unprecedentedly large size where it hovered, on the edge of sustainability until the crushing blow of human hunting destroyed them.

White-footed mouse. Photo by D.G.E. Robertson. Wikimedia Commons

The extinction of the passenger pigeon may also be having another ongoing impact here in the 21st Century. The absence of the pigeon means that there is more mast available to other mast consuming species. One of these mast consuming species is the white-footed mouse whose North American population has greatly increased greatly through the 20th and 21st Centuries. The white-footed mouse is also the major intermediate host for the bacterium that causes Lyme disease (Borrelia burgdorferi). Possibly, the extinction of the passenger pigeon is one of the contributing factors to the recent epidemic explosion of Lyme disease throughout the northeastern United States.

The extinction of the passenger pigeon shocked the people of the early 20th Century. It led to consideration and adoption of a wide range of conservation programs and continues to serve as a viscerally real lesson into the potential damage that uncontrolled human activity can have on natural species and ecosystems.

Posted in Bill's Notes | 1 Comment

Signs of Summer 5: The Virosphere!

Influenza virus, TEM (colorized). Photo by C. Goldsmith, CDC, Wikimedia Commons

(Click here to listen to an audio version of this blog!)

A couple of months ago an old friend and former Penn State colleague sent me an email in which she wrote: “Just wondering if all viruses are bad and wreak havoc?   Do some viruses do good things?  What is the overall function of them?   Just what is the purpose of a virus on this earth, and how did it help get us to where we are today? I’m just trying to look at the bigger picture of things.”

I promised that I would pull something together for her, and after mining through some of my old Cell and Molecular Biology lectures about viruses and several recent papers on them, here is what I hope to be the “bigger” picture about viruses.

There are two, typical starting points in any discussion about viruses. The first concerns how small and simple in structure they are, and the second is how abundant and diverse they are.

Size:

Most viruses range in size between 10 and 300 nano-meters. A nano-meter is one billionth (10-9) of a meter. For comparison,an average cell in your body is about 100 micrometers in diameter and an average bacterium is about 2 micrometers in diameter. A micrometer is one millionth (10-6) of a meter. So, without dwelling too much on the math, by volume an average cell in your body is a hundred million to a billion  times bigger than a virus! Most viruses are so small that they cannot be seen with a light microscope, they can only be visualize with an electron microscope.

Simple diagram of a virus. Figure by domdomegg, Wikimedia Commons

Structure:

Viruses are extremely simple. They consist of a core of a nucleic acid (either DNA or RNA) surrounded by a “capsid” made up of proteins that is then, in some viruses, further surrounded by an “envelope” of lipids that is studded with glycoproteins. Viral nucleic acids typically encode the information for 30 or 40 genes, and these genes encode the information for the synthesis of a variety of molecules including the components of the viral capsid and most of the envelope. Viruses must utilize the metabolic machinery of a living cell to replicate themselves since they lack both energy generating systems for ATP and ribosomes for protein synthesis.

There, though, some “big” viruses out in nature. Recently, while exploring the waters of an artificial lake in Brazil, scientists found a virus that contains 74 genes! And, 68 of these genes have never been seen in a virus before!

Abundance:

How many virus “particles” exist on Earth? It is estimated that there are 1030 viruses in the Earth’s oceans and possibly an equal number on land and in the atmosphere. Sometimes it is hard to grasp the size of number expressed as exponents, but there are estimated to be “only” 1023 stars in the entire Universe! So, there are ten million times more viruses on Earth than there are stars in all the skies everywhere!

Another way to visualize this mind boggling abundance is to recognize that there are 50,000 viral particles in every drop of sea water, and, according to researchers at Virginia Tech (Environ Sci Letters, 2016) 10,000 viral particles in every millimeter of air. We are constantly introducing these viruses in to our lungs with each breath that we take!

We are absolutely surrounded by viruses!

Ebola virus (colorized SEM). U.S.Agency for International Development. Wikimedia Commons

Diversity:

Scientist have described and identified about 7000 species of viruses, but estimate that there may be millions or even trillions of actual species of viruses on Earth. Mathew Sullivan at Ohio State, for example, has thus far found (but not completely described or named) 200,000 different virus types in sea water!

If you consider all of the genetic information in the living systems on Earth, there is probably significantly more information contained in the summed set of the short, nucleic acid strands housed inside of viruses than in all of the information encoded in the long strands of DNA and RNA contained within every cellular, living organism (plant, animal, protist, fungi and bacteria). Viruses represent, then, not only a vast reservoir of genetic information and potential, but, and this may be the ultimate “function” of viruses in nature, viruses not only carry all of this genetic information, but they are also able to transfer this information between all types and all manners of cells.  This ability to “horizontally” transfer genetic information between often totally unrelated species, may be a key factor in generating unique genetic combinations and driving the evolution of new species on Earth!

This is the “big picture!” This is what my friend was asking about! Viruses inject whole sets of genes into organisms and some of these genes work their way into the host’s cellular DNA. If the cells receiving these genes are reproductive cells (sperm or ova), then those genes will be passed along to the offspring of that individual. This is an incredibly more rapid mechanism for increasing genetic variability than simple nucleotide by nucleotide mutation of the host DNA!

Often these viral DNA inclusions are “silent” in the host cell, so no changes are seen in the organism. Sometimes, the impacts of these viral genes are disease and cell (or even organism) death. Sometimes, though, this additional genetic information conveys a fitness edge to the new organism, and via Natural Selection and evolution that more fit individual will predominate in its environment. A virus, then, can trigger a sudden and substantial change in an existing species!

It is possible to examine an organism’s DNA and pick out the viral sequences that has been added to it. In humans, for example, 8% of the 3 billion base pairs in the genome are from viruses. That means that there are 240 million viral nucleotide sequences in the average human genome! Some of these viral sequences do very important things. The genes that form the placenta, for example, are dominated by viral information! This suggests that the evolution of the placenta may have come about from a sequence of viral infections!

SARS-CoV2. Figure by Scientific Animations, Wikimedia Commons

Some recent published research about viral gene contributions include a study on sponges in which viruses contributed genetic information that enabled sponges to modulate their immune functions to better tolerate absolutely essential symbiotic bacteria (a 2019 paper in Cell Host Microbe). Also, a joint German and American research team studied heterotrophic zooplankta called “choanocytes” and found that they used viral DNA to established a rhodopsin based, non-chlorophyll photosynthetic energy system that augmented their typical heterotrophic life style! In Australia, an RNA virus that infects koala bears can cause leukemia and lymphoma and an increased susceptibility to chlamydia infections. This virus, though, has inserted itself into the koala’s DNA and become an inherited part of the koala genome. In some koala populations this viral sequence has mutated and may now be conveying some health benefits to the koalas!  This report was published in the journal Cell last fall.

Of the 7000 or so species of viruses that have been described only 200 affect humans. Viruses have to enter cells in order for their genes to hijack the metabolic machinery of the cell to make more viruses. Entering a cell is not an easy thing even for something as small as a virus. On the cell membrane of a living cell are numerous proteins that act as enzymes or chemical receptor sites,  or they allow and regulate the movement of many ions and molecules in and out of the cell. Often these membrane proteins are the doorways by which a virus enters a cell. The virus, though, has to fit very precisely into these channels in order to pass through them. Viruses that can pass through one species’ type of channel protein might not fit into a similar channel protein of a different species. So, many viruses can only infect certain species!

Life Cycle of SARS-CoV2. Figure by V. Asenio, Wikimedia Commons

The novel corona virus that cause COVID 19 is “SARS-CoV2.” I talked about this virus and what we initially knew about its disease in a special blog back in March 2020. SARS-CoV2 enters cells via the angiotensin converting enzyme 2 (ACE2) receptor that is located on the outer surface of the cell membrane. ACE2 normally functions to break down angiotensin II a protein that is part of a hormonal system that helps to control blood pressure. The studded, surface proteins of the corona virus (the physical feature that gives it its “crown-like” appearance on electron micrographs) match up to the ACE2 receptor and “open” the protein for the virus’s passage. Once inside the cell, the RNA contained in the corona virus takes over the cell’s metabolic machinery and begins to make huge numbers of new viruses. Eventually the infected cell ruptures and spills out the newly synthesized viruses which may then infect more cells in the host individual or be released in exhalations or coughs to potentially infect other people.

Variations in the molecular structure of ACE2 receptor (affected by genes or, possibly, by gender) may determine whether a particular individual “gets” COVID19 infections or it may affect how severe that infection might be.

So, we are all constantly bombarded by incredible numbers of an almost infinite variety of viruses. Most of these viruses cannot affect us since they are unable to cross though our cellular membranes. Viruses, though, are constantly changing and if a change involves its interaction with cellular proteins then that virus that once only affected, say, a chimpanzee or pangolin, may suddenly affect humans often with catastrophic consequences.

Viruses may represent the earliest life forms on Earth or they may have come about from the shed nucleic acids from the earliest cellular life forms. Either way, they represent a vast reservoir of genetic information that is flowing in between and constantly changing all of the other living species on Earth.

 

 

 

 

Posted in Bill's Notes | Leave a comment

Signs of Summer 4: Natural History of the American Beech (part 2)

American beech in winter. Photo by Sixflashphoto, Wikimedia Commons

(Click here to listen to an audio version of this blog!

(Please note: the Campus Nature Trail at Penn State New Kensington is no longer accessible for hiking. The notes and observations about the trail that are included in this essay were made in the early 2000’s.)

Walking in the woods in the winter is good time to assess the number of beech trees and saplings present because of their tendency to retain their senesced leaves through the winter. This phenomenon called marcesence (Finley, 2012).

Here is a short excerpt from my 2010 “Winter Walk on the Nature Trail:”

“The American beech trees, in their usual fashion, have hung onto to last year’s leaves. Their “autumn” will not end until their new buds begin to open in the late spring. The dry, brown leaves rattle in the breeze making one of the few sounds we hear along the trail.”

Leaf loss, as I have written before, is a purely “economic” decision for a tree. Leaves are the tree’s organs for photosynthesis and energy acquisition, but leaves also lose incredible quantities of water via transpiration. With the approaching winter the leaves for all deciduous trees are shed primarily to help the trees to withstand the very dry conditions of winter. This seasonal leaf loss also recognizes that the freezing of leaf cells’ cytoplasm and interstitial fluids would cause such widespread damage to their cellular  structures that they would be incapable of any future photosynthesis.

When the deciduous trees get ready to shed their leaves, they undergo several well defined stages of change. First, in response to the length of the dark period of the day reaching a critical length, they begin to generate large numbers of cells right at the junction of the leaf’s stem and its branch. These cells greatly increase in number but not, at first, in their individual sizes. This layer of cells (the “abscission layer”) slowly starts to interfere with the flow of sugars out of the leaf and the flow of nutrients into the leaf.

The lack of nutrients causes the leaf to stop synthesizing new chlorophyll molecules. Chlorophylls are, of course, the functional pigments of photosynthesis and also the pigments that give plants their characteristic green colors. Initial cessation of chlorophyll production makes the leaves appear a bit paler and less intensely green than they were during the height of summer. These trapped chlorophylls in some leaves may also trigger the synthesis of anthocyanin pigments (red or purple pigments).

Autumnal leaves of the American beech. Photo by N. Toneli, Flickr

As the chlorophyll levels continue to decline other pigments (the “accessory” pigments of photosynthesis: the carotenoids and xanthophylls) that had been present in the leaves all summer long are revealed. These pigments, then, “turn” the leaves orange (from the carotenoids) or yellow (from the xanthophylls) before they finally fall from the tree. The golden-bronze leaves of the autumn American beech, then, is a mix of all three of these types of leaf pigments.

In most tree species, the cells in the abscission layer secrete enzymes that break the attachment of the leaf to its stem. A sudden frost or freeze may reduce the production or action of these abscission enzymes preventing the release of the leaves from their tree. There are, though, some species of trees in which these abscission enzymes are not immediately active at all. These include many types of oak, witch hazel, hornbeam and hophornbeam and American beech. These trees, then, especially their smaller/younger individuals, keep their leaves throughout the winter (Finley, 2012).

What is the benefit of marcescence? The attached, rattling leaves may discourage deer browsing (Svendsen, 2001). It may also give the leaves a period of photodegradation that makes their eventual decomposition more efficient. It may also keep the leaves from being decomposed during the winter (the non-growth period for the tree) and thus make the leaf nutrients more directly available to the growing tree in the spring and summer (Angst et al., 2017).

Hiking along the Rock Furnace Trail in Kiski Township in 2007, I made the following observation:

Beech drops. Photo by Blue Ridge Kitties. Flickr

“We continued down to the Roaring Run stream. All along the path the bright, red berry clusters of trillium stood out sharply against the brown leaf litter and the dark green fronds of the ferns. In the spring, this section of the trail is a riot of white trillium flowers. The evidence of the pollinating success of the plants was now all around us. The trillium berries are commonly gathered, dispersed, and buried by ants as a cold season food source. Lost and forgotten berries germinate in the spring and advance the spread of these magnificent wildflowers.  Less obvious than the trillium berries were the brown, foot high stems of a plant called “beech drops” (Epifagus virginanis). Beech drops look at first like the dry, dead stalks of some woody herb. On closer examination, though, the soft flexibility of the stalks and the tiny, delicate brown flowers indicate that these plants are, indeed, alive. The total lack of green color in the plant parts, though, identifies beech drops as a non-photosynthesizing, parasitic plant that is similar in ecology to the plants “Indian pipe” and “squawroot” (both of which are found on our campus nature trail). The stems and flowers of beech drop connect to an extensive, underground root system that is intimately intertwined with the roots of the surrounding beech trees. The plants draw nutrients out of the tree roots and live in a parasitic symbiosis with them. Recent studies involving Indian pipes, though, have shown that this type of symbiosis may be more complex than was formerly thought. There is the suggestion that some trees in association with Indian pipes actually grow better and obtain more nutrients from their supportive soil volume. The symbiotic connections of the tree and plant roots actually increase the absorptive surface area of the root system to the great benefit of both the tree and the plant. Possibly beech drops also assists the root system functioning of the beech tree in a similar manner.”

Beech drops, though, are classified as a root parasite of American beech trees not a mutualistic symbiont, although it is universally stated that the attachment of the beech drops does not adversely affect the health of the beech trees. Further, the presence of beech drops is a forest is considered to be a sign of overall forest health and stability (Tsai and Manos, 2010).

Beech bark disease, Photo by E. Sagor, Flickr

A very significant disease of American beech trees is Beech Bark Disease (BBD). BBD is caused by the interaction of the alien exotic insect the beech scale (Cryptococcus fagisuga) (which was introduced into North America from Europe in 1890) and the fungus Necatria coccinea (also an introduced, exotic species) or the native fungus Necatria galligena Houston and O’Brien, 1983). This disease kills 50 to 85% of infected trees within ten years of their initial infection. BBD has spread from its initial introduction site in Nova Scotia across southeastern Canada, New England, New York, Pennsylvania, West Virginia, west to Michigan and Wisconsin and south down the spine of the Appalachian Mountains (Forest Invasives Canada, 2015). Ongoing research is examining enzyme characteristics and bark phenolic concentrations to try to understand the mechanism of the observed resistance of some beech trees to BBD (Houston and Houston, 1994)(Ostrofsky et al., 1984).

So, I am back in front of the large American beech along the Ravine Trail. A hundred years ago or so the parental tree of this beech flowered in early May shortly after its leaves began to emerge. The parental tree, like all beeches, had both male and female flowers. The female flowers on a particular tree mature first to reduce the chances of self-pollination. The pollen from the male flowers is then dispersed on the wind. Beech flowers are often under the threat of destruction by a late spring frost which, with some frequency, derails the production of beech nuts (Tubbs and Houston, 1990). But, since we ended up with a tree, at least some of the flowers survived and were fertilized this particular year.

After fertilization, the beechnut slowly developed and matured through the rest of the growing season. It ripened between September and November and fell from the parental tree when the encasing burr opened shortly after the first hard frost (Tubbs and Houston, 1990). The nuts, as we mentioned earlier, are eaten by many species of birds and mammals. These animals, though, can also, especially in years when there are very abundant beechnuts, be actively involved in spreading the nuts. Blue jays and gray squirrels are especially important dispersers of beech nuts. Most of the nuts, though, that fell from the parental tree simply landed on the soil and leaf litter under its branches and, if not eaten, waited out the winter for possible spring germination.

Photo by D. Ramsey, Wikimedia Commons

Germination of the moisture loving American beech, ironically, occurs most efficiently on micro-sites that are themselves not excessively wet. These potential germination sites could be either on exposed mineral soil or on piles of leaf litter. They could also be under fern or raspberry cover. The emerging seedling survives best under some degree of shading. Small, protected, partially shaded openings are especially favorable for beech seedling development, although, even under very dense, continuous stands of trees, large numbers of very slowly growing beech seedlings can be found (Logan, 1973). The seedlings are growing so slowly, in fact, that after 6 years the seedling may only be one foot tall and after 25 years may only reach heights of seven feet (Tubbs and Houston, 1990).

Our tree, then, grew very slowly under shade suppression for many years, possibly for several decades. Some fortuitous, for the beech, event in the overstory opened the canopy enough to allow entrance of sufficient sunlight to fuel the beech’s growth.  One hundred years later, after avoiding serious damage from the many species of decay fungi which plague the species and the many types of sucking and defoliating insects that can stress or even kill the tree, the tree before us stands large and sound.

 

References (for “American Beech, Parts 1 and 2”):

Adirondacks Forever Wild, 2020. Trees of the Adirondacks: American beech.

https://wildadirondacks.org/trees-of-the-adirondacks-american-beech-fagus-grandifolia.html. Accessed April 28, 2020.

Angst, Šárka; Cajthaml, Tomáš; Angst, Gerrit; Šimáčková, Hana; Brus, Jiří; Frouz, Jan. “Retention of dead standing plant biomass (marcescence) increases subsequent litter decomposition in the soil organic layer”. Plant and Soil418 (1–2) (2017): 571–579

Brisson, Jacques, et al. “Beech-maple dynamics in an old-growth forest in southern Québec, Canada.” Ecoscience 1.1 (1994): 40-46.

Carpenter, Roswell D. American beech. Vol. 220. US Department of Agriculture, Forest Service, 1974.

Faison, Edward K., and David R. Houston. “Black bear foraging in response to beech bark disease in northern Vermont.” Northeastern Naturalist 11.4 (2004): 387-394.

Finley, J. 2012. “Winter leaves that hang on.” Penn State Extension: Forest Management Resources. https://ecosystems.psu.edu/research/centers/private-forests/news/2012/winter-leaves-that-hang-on.Accessed April 28, 2020.

Forest Invasives Canada. “Beech Bard Disease.” 2015. https://forestinvasives.ca/Meet-the-Species/Pathogens/Beech-Bark-Disease#70228-distribution. Accessed April 30, 2020.

Forester, J. A., G. G. McGee, and M. J. Mitchell. “Effects of beech bark disease on aboveground biomass and species composition in a mature northern hardwood forest.” Journal of the Torrey Botanical Society 130 (2003): 70-78.

Fowells, H. A. “Silvics of forest trees of the United States, agriculture handbook No. 271.” Washington DC: United States Department of Agriculture (1965).

George, Lisa O., and F. A. Bazzaz . “The fern understory as an ecological filter: emergence and establishment of canopy‐tree seedlings.” Ecology 80.3 (1999 a): 833-845.

George, Lisa O., and F. A. Bazzaz. “The fern understory as an ecological filter: growth and survival of canopy‐tree seedlings.” Ecology 80.3 (1999 b): 846-856.

Harlow, William M., et al. “Textbook of dendrology 6th edition.” (1979).

Hepting, George Henry. Diseases of forest and shade trees of the United States. No. 386. US Department of Agriculture, Forest Service, 1971.

Horsley, Stephen B. “Allelopathic inhibition of black cherry by fern, grass, goldenrod, and aster.” Canadian Journal of Forest Research 7.2 (1977a): 205-216.

Horsley, Stephen B. “Allelopathic inhibition of black cherry. II. Inhibition by woodland grass, ferns, and club moss.” Canadian Journal of Forest Research 7.3 (1977b): 515-519.

Houston, D. B., and D. R. Houston. “Variation in American beech (Fagus grandifolia Ehrh.): isozyme analysis of genetic structure in selected stands.” Silvae Genetica 43.5 (1994): 277-284

Houston, D. R. and J. T. O’Brien. “Beech Bark Disease.” Forest Insect and Disease Leaflet 75. USDA. 1983.

Latty, Erika F., Charles D. Canham, and Peter L. Marks. “The effects of land-use history on soil properties and nutrient dynamics in northern hardwood forests of the Adirondack Mountains.” Ecosystems 7.2 (2004): 193-207.

Loach, K. “Shade tolerance in tree seedlings: II. Growth analysis of plants raised under artificial shade.” New Phytologist 69.2 (1970): 273-286.

Logan, K. T. “Growth of tree seedlings as affected by light intensity V. White Ash, Beech, Eastern Hemlock, and general conclusions.” Publ Dep Environ Can For Serv (1973).

Lutz, Harold J. “Original forest composition in northwestern Pennsylvania as indicated by early land survey notes.” Journal of Forestry 28.8 (1930): 1098-1103.

Morris, Ashley B., Randall L. Small, and Mitchell B. Cruzan. “Variation in frequency of clonal reproduction among populations of Fagus grandifolia Ehrh. in response to disturbance.” Castanea 69.1 (2004): 38-51.

Old Growth Forest Network. (2020). Heart’s Content National Scenic Area: Allegheny National Forest.    https://www.oldgrowthforest.net/pa-hearts-content-national-scenic-area-allegheny-national-forest (accessed April 28, 2020)

Ostrofsky, W. D., W. C. Shortle, and R. O. Blanchard. “Bark phenolics of American beech (Fagus grandifolia) in relation to the beech bark disease 1.” European journal of forest pathology 14.1 (1984): 52-59.

Royo, Alejandro A., and Walter P. Carson. “Direct and indirect effects of a dense understory on tree seedling recruitment in temperate forests: habitat-mediated predation versus competition.” Canadian Journal of Forest Research 38.6 (2008): 1634-1645.

Rushmore, Francis M. “Silvical characteristics of beech (Fagus grandifolia).” Station Paper NE-161. Upper Darby, PA: US Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 26 p. 161 (1961).

Tsai, Yi-Hsin Erica; Manos, Paul S. “Host density drives the postglacial migration of the tree parasite, Epifagus virginiana”Proceedings of the National Academy of Sciences of the United States of America107 (39) (2010): 17035–17040.

Tubbs, Carl H., and David R. Houston. “Fagus grandifolia Ehrh. American beech.” Silvics of North America 2 (1990): 325-332.

Svendsen, Claus R.. “Effects of marcescent leaves on winter browsing by large herbivores in northern temperate deciduous forests.” Alces 37(2) (2001): 475-482.

Whitney, Gordon G. “The history and status of the hemlock-hardwood forests of the Allegheny Plateau.” The Journal of Ecology (1990): 443-458.

Whitney, G. G. “1994: From coastal wilderness to fruited plain. A historv of environmental change in temperate North America, 1500-present. Cambridge: Cambridge University Press.” (1994).

 

Posted in Bill's Notes | Leave a comment

Signs of Summer 3: Natural History of the American Beech (part 1)

(Click here to the listen to an audio version of this blog!)

(Please note: the Campus Nature Trail at Penn State New Kensington is no longer accessible for hiking. The notes and observations about the trail that are included in this essay were made in the early 2000’s.)

Spicebush Trail. Photo by D. Sillman

(References will be listed next week after Part 2!)

The section of the Campus Nature Trail called the Spicebush Trail gets its name, logically, from the dense, surrounding growth of spicebush (Lindera benzoin). The tall arching branches of these shrubs form a tunnel over a good part of the trail, and the scent of their aromatic leaves is quite pleasant in the damp, cool mornings of late spring and early summer. This tunneled trail goes down a gentle slope and ends at a footbridge that crosses a small, seasonal creek. If you cross the bridge, you can walk to stand of witch hazel (Hamamelis virginiana) and overlook a low, oxbowed section of streambank that is full of skunk cabbage (Symplocarpus foetidus). If you turn left at the bridge, you can walk up the steep Ravine Trail to the drier, upland trail system that crisscrosses through an oak and poplar forest.

A few steps up the Ravine Trail is a large American beech tree (Fagus grandifolia). Its trunk diameter at breast height is almost two feet, and it stands over 60 feet tall.  Its very distinctive, light gray bark is lumpy and marked by old wounds and frost scars that have repaired themselves in thick dark circles and lines. Fortunately, no one has carved their initials or statements of love and devotion into the bark of this tree. Beech trees are frequently decorated with messages and graffiti, and these scars carved into the bark will persist for the life of the tree (Rushmore, 1961).

The bark of the beech is also one of its significant weaknesses. Its thin, fragile nature makes the tree vulnerable to insect damage, disease and fire (Tubbs and Houston, 1990). There are more than 70 species of decay fungi that attack American beeches, far more than affect any other hardwood species (Hepting, 1971). The common observation of large, old beech trees having hollow trunks and rotting limbs is reflective of its great sensitivity to fungi.

Photo by K. McFarland. Flickr

Unlike most other hardwood trees, the American beech retains its smooth bark throughout its “mature” years. The American beech can live for three hundred to four hundred years and can frequently reach heights of eighty feet and diameters in excess of three feet. In the shaded conditions of a forest stand, the American beech forms a long, straight, massive trunk that rises into a small, dense crown of foliage. In sunnier, more open sites, the American beech forms a short (although still massive!) trunk that diverges into a large number of horizontal branches that make a huge, widely spreading crown.

The American beech is found in sites that have moist soils. Beeches are especially abundant along streams and creeks, in bottom lands, and in shaded, protected ravines. Any site, though, with adequate soil moisture will support the American beech.  Its root system is shallow and widely spreading which adapts it well to wet conditions. It is able to sprout new seedlings from its roots and often dense thickets of these root-sprouted seedlings are found around older, undisturbed trees (Tubbs and Houston, 1990). The tendency of beech to root sprout affects the genetic distribution of the beech trees in a forest. It causes them to grow in clonal clumps especially on sites that have been stressed or disturbed (Houston and Houston, 1994)(Morris et al., 2004).

The leaves of the American beech are also quite distinctive. They are from two and a half to six inches long and two and a half inches wide, elliptical in shape with many parallel side veins and coarse, saw-toothed edges. They are dull green above and lighter green below and turn yellow or brown in the autumn (Harlow, William M., et al. ,1979).. The leaves may remain attached to their trees through the winter (discussion below). These leaves decompose relatively slowly and are, therefore, found in thick layers on the soil surface beneath the trees (Forrester, McGee and Mitchell, 2003).

There are a number of American beech trees along the ravine and many more particularly on the north facing side of the slope down to the creek. A few of the trees are as large as the beech on the Ravine Trail, but most are smaller. Throughout the surrounding, brushy forest there are many beech seedlings and saplings and pole trees, too. Beeches seem to be thriving in this section of the forest.

There is an American beech in Michigan (mentioned in Tubbs and Houston, 1990) that stood 161 feet tall and was 53 inches in diameter, and another (mentioned in Carpenter, 1974) that was 91 feet tall with a diameter of 70 inches. Often these very large beeches are hollow due to heartwood rot.

The American beech was, according to the earliest land survey, “witness” tree records, the most abundant tree across the northern tier of Pennsylvania (Lutz, 1930)(Whitney, 1990, 1994). In Hearts Content National Scenic area in Warren County, Pennsylvania there is a patch of virgin forest that includes a number of American beech trees that are 300 to 400 years old. They are being ravaged, though, by Beech Bark Disease and a host of insect pests and may be approaching the end of their lives (Old Growth Forest Network, 2020).

The American beech is a tree of eastern North America. It is found from Canada to Florida and west to Wisconsin in the north and Texas and Oklahoma in the south. Prior to the last glaciation, though, its range was thought to extend all the way across the continent to California (Rushmore, 1961)

There are two critical physiological characteristics of the American beech that enable them to persevere and thrive in their habitats. These same two characteristics, though, also help to explain why the vast beech forests of northern Pennsylvania did not recover from the trauma of the clear-cutting that occurred a little over a century ago when the American beech went from the numerically dominant tree in these forests to a relatively uncommon species confined to stream sides and wet ravines.

Photo by J. Barker, NPS

First characteristic: the American beech needs a great deal of water to survive. It uses twice the water for growth and transpiration than that used by either oaks or pines (Tubbs and Houston, 1990). The consequence of this characteristic is that beeches must grow in places that are very moist. This high moisture requirement also affects the distribution of the American beech both geographically and topographically. Locales with very high summer temperatures are avoided (the American beech is a tree of high altitude in the southern extremes of its range), and sun drenched, south facing slopes are less preferred than the shadier, and thus wetter, north facing exposures (Fowells, 1965).

Second characteristic: the American beech has a very slow rate of metabolism. This feature enables the tree’s seedlings and saplings to persist in low energy, suppressed states for many years under dense, shading over-stories as they wait for possible breaks in the canopy above them to release them into a growth phase. American beech is the most shade tolerant tree throughout most of its range ( Loach, 1970), but its slow metabolic rate effectively prevents it from competing with faster growing hardwood species when sunlight becomes available. If there are white ash trees or birches or red maples in the under-story mix, these species will spring up into the open canopy at growth rates much greater than the American beech (Logan, 1973).  For beech to succeed, then, it must be the predominate seedling in the under-story at the moment of release.

The American beech, then, will reproduce and succeed on a site that is cool, moist, and well shaded. Its success will be even more pronounced if the levels and duration of these cool temperatures, high moisture levels, and lack of sunlight are so stressful to other, less tolerant, hardwood species that many or most of their seedlings fail and die. The American beech’s ability to endure and grow very slowly for decade upon decade in these stressful conditions is the essence of its competitive edge. Alterations of a site that generate widespread soil and litter exposure to direct sunlight (and clear cutting would be an extreme example of such an alteration) will warm and dry the soil/litter system, and stimulate growth in the faster growing, less shade tolerant tree species. Such an alteration, then, erases the American beech’s competitive edge and makes the success of other tree species (like birch, black cherry, red maple, white ash, etc.) more probable.

Beech mast. Photo by D. Mullen, Flickr

Beech mast is an important food source for many birds and mammals (including black bear, white-tailed deer, chipmunks, foxes, red squirrels, gray squirrels , porcupines, martens, mice, ruffed grouse, red-headed woodpeckers, white-breasted nuthatches and blue jays) (Tubbs and Houston, 1990)(Faison and Houston, 2004) (Adirondacks Forever Wild, 2020). Beech mast was also the favorite food of the now extinct passenger pigeon ( Ectopistes migratorius ). James Audubon described the formation and movement of the great flocks of these birds as primarily a behavior designed to seek out and consume beech nuts (Rushmore, 1961). Many of these birds and mammals contribute to the widespread dispersion of beech seeds through their feeding on and possibly burying and caching of the beech mast.

Other parts of a beech tree also supports a wide variety of bird species. White-throated sparrows eat buds and blossoms in the spring, hairy woodpeckers and scarlet tanagers preferentially forage for insects among its branches, wood ducks utilize tree holes in beeches for their nests, and Cooper’s hawks, northern goshawks, American redstarts and a long list of other birds make their nests in beech branches. (Adirondack Forever Wild, 2020).

Beech trees are also very important in the quality and nutrient composition of the forest soils. Beech leaves are rich in nitrogen (they contain 3% nitrogen, the highest value of any tree in the forests of eastern North America) (Latty, Charles and Marks, 2004). Its leaves also tend to accumulate under the tree of origin and form thick, slowly decomposing mats of organic materials which effectively mulch out possible nutrient and light competing herbaceous growth and other tree species (Forrester, McGee and Mitchell, 2003).  This can be very important to the reproductive success of the beech because sites with thick, forest floor underbrush can shelter large numbers of beech mast consumers that are capable especially in low mast production years of eating a very high percentage of a tree’s mast production (Royo and Carson, 2008).

Ferns can have a negative effect on the rate of seed germination and growth of seedlings of many species of trees (including birches, black cherry, pines, and oaks)  (Horsley, 1977 a and b) (George and Bazzaz, 1990 a and b). Neither ferns nor raspberry cover, though, have, however,  a negative effect on the germination and survival of American beech (Tubbs and Houston, 1990).

Photo by K. Schultz, Wikimedia Commons

The American beech’s ability to sprout from the stumps of young trees gives it a competitive edge over non-sprouting species in any successional race triggered by disturbance.  The growth rates of the sprouts, though, are much slower than the seedling growth rates of the less shade tolerant hardwood species with which they typically compete.  A significant, successional advantage that American beech sprouts and seedlings do have over all of their potential hardwood competitors, though, is the beech’s “virtual immunity to deer browsing.” White-tailed deer, which are one of the primary sculpting forces of our present day forests in Pennsylvania, seldom eat beech seedlings or sprouts (Tubbs and Houston, 1990).

The ability of the beech to vigorously root sprout, its high levels of shade tolerance and very low metabolic rate, its ability to mulch out forest floor competitors, its ability to tolerate the potential allelopathic effects of ferns and other forest floor plants and its “immunity” from deer browsing allow the species to persist in and even come to dominate many mixed hardwood forests. In beech and sugar maple forests in Ontario, for example, it is expected that beech trees will predominate over the maples over successional time (Brisson, et al., 1994).

(Next week: the American beech, Part 2!)

 

Posted in Bill's Notes | Leave a comment

Signs of Summer 2: The Cavity Nesting Team Year #6!

Photo by D. Sillman

(Click here to listen to an audio version of this blog!)

Over the past six years I have written a number of articles about our Cavity Nesting Team study up at Harrison Hills Park in northern Allegheny County. Each year of our study has contributed significantly to our understanding of the ecology and reproductive biology of two especially important cavity hole nesters: bluebirds and tree swallows.

Our findings from 2015 helped us better understand the optimal location variables for our nesting boxes (and our relocated 2016 boxes were almost all utilized for nests!). Our 2016 data helped us design two experiments for 2017 in which we tried to regulate house wren nesting in our boxes (house wrens are very destructive to nesting bluebirds and tree swallows). The results of our experiments in 2017 were not very successful, but we re-tuned some of our 2017 ideas for the 2018 season and achieved a sustainable equilibrium between bluebirds, tree swallows and house wrens.

In 2018 we had a very warm and wet spring and summer, and, although we had a record number-to-date of bluebird nests (23), we also had a record number of nests with no eggs (6) and ones that had a high degree (50% or more) of egg mortality (also 6). Consequently, we had the second lowest number of eggs in any year of our study (just 67) and the lowest number of fledglings (only 46). We are not sure if these unusual weather conditions contributed to increased activity of nest parasites or predators or if the heat and the rain might have limited the food supply or directly stressed either the adult birds or the nestlings.

Seventeen year cicada. Photo by M. O’Donnell Flickr

In 2019 we experienced the emergence year of our local seventeen year cicadas! We weren’t sure if the June explosion of cicadas would have a positive or a negative effect on the cavity nesting species. Harrison Hills Park, though, had a great abundance of seventeen year cicadas! We were very curious if the bluebirds or the swallows would eat the cicadas or if these large, flying insects would interfere with the birds’ food gathering or nesting patterns. We also planned through our 2019 collection season to be very diligent in removing the display nests (also called “dummy nests”) that the male house wren builds to convince a female that he is worthy of reproduction in an attempt to discourage their mating.

Bluebirds and tree swallows have a very specific mating and nesting pattern that has been followed each of the years of our study. Bluebirds nest early in the spring (April and May) and produce about two thirds of their yearly eggs and fledglings in this reproductive event. They then nest again later in the summer (July and August) producing the rest of their annual eggs and fledglings. Tree swallows mate and nest in between these two bluebird nesting phases (in late May and June)! This pattern reduces competition for nesting sites (many of the early bluebird nesting boxes are then used by the swallows and a few are subsequently used by the late nesting bluebirds!

In 2019, this cycle was compressed into a much earlier time frame. The bluebirds started nesting in March and then re-nested in June, and by mid-July all of the bluebird reproductive activity was over for the year! The swallows, still fitting their nesting in between the bluebird nesting phases, started nesting in late April and early May and were done by the second week in June! We had a record number of bluebird nests and eggs (24 nests and 101 eggs), and 7 tree swallow nests with 32 eggs. Once again, though, the tree swallows mainly nested in the northern parts of the park away from the large pond in the south! The pond would seem to be an ideal habitat for the swallows, so its exclusion is very curious. Also, none of the volunteers observing the nesting boxes saw either a bluebird or a tree swallow eating a periodical cicada.

Tree swallow. K. Thomas, Public Domain

Although the egg production was very robust, the 2019 fledgling success rate for both bluebirds and tree swallows was quite low due to a very intensive impact of nest predators (black snakes, raccoons etc.). Fourteen bluebird nestlings and 20 tree swallow nestlings were eaten by nest predators. We realized that we had to do something to make our nest boxes safer and developed a plan to install predator guards for the 2020 nesting season.

Our house wren control was very effective for the 2019 season. Our diligence in removing the dummy nets discouraged the wren use of our nesting boxes. There were a total of 9 house wren nests but only 3 had eggs. There were only 4 house wren fledglings observed in 2019!

This year’s 2020 Cavity Nesting Team consists of 16 volunteers: Sharon Svitek and Lisa Kolodziejski take turns monitoring the boxes in and around the “High Meadow.” Dave and Kathy Brooke check the boxes around the “Bat House Meadow.”  Dave Rizzo and Megan Concannon and Marianne Neal take turns monitoring the boxes in the fields near the Environmental Learning Center, and Paul Dudek and Donna Tolk check the boxes at the park entrance and around the soccer fields in the southern end of the park. The boxes around the “south” pond are checked by David and Kielie Ciuchtas and Denise Kelly.  Patrick and Mardelle Kopnicky serve as resource people to help the new volunteers get adjusted to the program and to remind the rest of us about our working models and past observations, and Deborah and I are working this year as data compilers and reporters.

Our primary focus for 2020 is to see if our added predator guards reduced the predation pressure on our eggs and nestlings. Prior to this year 7 of our 29 boxes had predator guards. We added 15 new guards to our nesting boxes thanks to some volunteer work by an area boy scout and an immense amount of work by Dave Brooke (one of our volunteers) and a grant from Patrick and Mardelle Kopnicky.  So, now 22 of our 29 boxes are protected.

So what have we seen so far this year?

Bluebird eggs. Photo by C. Urick

Bluebird nesting started right at the first of April! We had 6 nests the first weekend we went out to count and 7 more the second weekend! Bluebirds were mating and building nests very early and very rapidly! By the end of the first week in June we already had 22 bluebird nests which is well on the way to setting a new nesting record! There were 67 bluebird eggs observed but only 25 fledglings so far (there are still 21 bluebird eggs out there that haven’t hatched yet). There has been, though, a very high nest mortality rate for bluebird nestlings. We have observed 16 dead, bluebird nestlings and have had to remove them from the nests. The nestlings, apparently, were abandoned by their parents and either died of starvation or exposure/hypothermia.

The spring was quite cold (it snowed in mid-April!), and we speculate that food for the bluebird nestlings may have limited. Parent birds will abandon a nest if they cannot find enough food for the nestlings. Several area bluebird keepers have indicated that they have had to augment the food supplies for their nesting bluebirds.

Tree swallow nests. Photo by T. Schweitzer, Flickr

We have also seen 12 tree swallow nests with 29 eggs. As of the first week of June, none of these eggs have yet hatched. We have also found 2 dead adult tree swallows in the nesting boxes. There was no indication of the cause of death, although weather may have been a contributing factor.

Our house wren control program seems to be working. We have only had 2 completed house wren nests with 11 eggs. None of the eggs have yet hatched. Our predator controls seem to be working well. There has been no evidence of nest predation in any of our nesting boxes.

So, 2020, like almost all of our observation years, is unique! We are seeing robust bluebird and tree swallow nesting that has generated a record setting pace of egg production. But, we are also seeing the unforgiving impact of weather fluctuations with the nest deaths of a significant number of nestling birds.

More news later!

 

 

Posted in Bill's Notes | Leave a comment

Signs of Summer 1: Short Blogs on Unrelated Topics!

My desk top

(Click here to listen to an audio version of this blog!)

I get ideas for blogs either from my own observations out in nature or from reading about observations in the scientific literature. I keep file folders open on the desktop of my computer, and when I come across an interesting article in one of the publications I read, I add to one of the files. When I get enough articles about a particular topic or when I see some connections between articles on somewhat different topics, I do some extra background reading to flesh out the ideas and then write about the articles.

Sometimes, though, there are articles that just don’t fit together with any other articles. They are often strange, wonderful, esoteric bits and pieces of research that deserved to be noticed and discussed, but by themselves wouldn’t rise to the typical 1200 + word length of these blogs. Today, though, I am going to talk about four of these unique articles that have been hanging around for a while on my computer. Here are some “short-blogs” for our Signs of Summer #1!

Two miles below the Earth’s surface

(this is from an article that an old student of mine, Chris Urik, called my attention to. Thanks, Chris!)

Sunrise dam open pit gold mine. Photo by Calistemon. Wikimedia Commons

Gold mines are the deepest human-made holes on Earth! One of these deep holes, the Moah Khotsong mine in South Africa, extends more than two miles below the Earth’s surface, and the rocks at the bottom of this mine are three billion years old! Water can get trapped in pockets and spaces in these deep rocks and become sealed off from any contact with the surrounding environment for many thousands of years. Recently, scientists sampling these hidden micro-pools found to their great surprise complex, living organisms inhabiting them!

Halicephalobus mephisto. J. Bracht. Wikimedia Commons

For example, in one water pocket that was dated to be five thousand years old a new species of nematode (called Halicephalobus mephisto) was found. This deep dwelling worm is 0.5 mm long and survives by feeding on chemosynthetic bacteria that form biofilms in the 37 degree C (99 degrees F) water. Halicephalobus mephisto’s  genus name means “he who loves not the light” in Greek, and its species name is from the devil, Mephistopheles,  in the legend of Faust. Popular news stories about this new nematode have referred to it as the “devil worm.”

Three other species of nematodes have also been described from these deep, rock water pockets along with flatworms, segmented worms, rotifers and even a crustacean. Fungi have also been found! All of this living biomass and all of this biological diversity is supported by the consumption of bacteria that, in turn, exist via the oxidation of a wide variety of inorganic atoms and molecules! This is an ecosystem that is far removed from the sun and photosynthesis. In fact, if the sun were extinguished and the Earth somehow survived, these tiny invertebrates and their trophic base of bacteria would continue to exist as long as the Earth’s heat (derived from the radioactive decay of unstable elements) persisted.

Amphibian Halloween Costumes

Hellbender salamander. Photo by B.Gratwicke. Wikimedia Commons.

Amphibians are the oldest group of terrestrial vertebrates. They arose during the Devonian Period of the Paleozoic Era some 370 to 400 million years ago and are the evolutionary forerunners of all of the terrestrial vertebrate groups. Most amphibians lay their eggs in water and have early life stages (larvae) that develop as aquatic organisms (tadpoles of frogs are an excellent example of this).  I have written a number of blogs about amphibians: I have talked about the wood frogs down at Ohiopyle ( see Signs of Spring 4, March 22, 2018), the amphibians in my yard ( Signs of Fall 5, October 6, 2016), and the hunt for salamanders at Harrison Hills Park (Signs of Summer 4, June 18, 2015).

I have also written about the massive, on-going extinction of amphibian species along with a few hopeful points about their persistence or recovery or reappearances (like the genetic insights recently made about the Chinese giant salamanders and the adaptations of Panamanian frogs to the deadly chytrid fungus, or the rare hellbender salamander caught in the nearby Kiskiminetas  River two summers ago (Signs of Summer 7, July 19, 2018).

Something that we didn’t know about amphibians, though, was that they decorate themselves with eerie, mostly green, biofluorescent markings as if they were going out trick-or-treating for Halloween.

Eastern tiger salamander. Photo by J. Lamb and M. Davis

In a paper published in Scientific Reports (February 27, 2020) two scientists from St. Cloud State University in Minnesota examined amphibians from eight salamander families, five frog families and one family of caecilians (limbless amphibians) at the Shedd Aquarium in Chicago. They exposed these living (or, in some cases, freshly dead) amphibians to blue light and found that all of them displayed green to yellow patterns of biofluorescence!

Blue light has the shortest wavelength (450 to 490 nm) in the color arrays of the visible light spectrum and, therefore, the greatest amount of energy. Blue light also behaves differently than the other visible light components of the spectrum: for example, the other light waves pass relatively directly through the atmosphere on their way to the Earth’s surface while blue light waves scatter and disperse when they strike water molecules or the other gaseous components of the atmosphere. This causes the sky to look blue!

Blue light’s potent energy content contributes to macular degeneration and also digital eye strain. It also alters triggers specific retinal input into the brain that stimulates brain activity and suppresses the production of the sleep inducing hormone, melatonin.

The proportion of blue light in an ecosystem’s ambient light spectrum increases in deeply forested, shady habitats. It also increases at twilight. Amphibians, then, who predominately live in shady habitats and display predominantly crepuscular to nocturnal activity, are exposed to significant levels of blue light. The wide range of blue light biofluorescence observed from the amphibian species in this study suggests that this tendency of biofluorescence is a feature that developed far back in the evolution of modern amphibians!

The researchers do not know why amphibians glow under blue light. They speculate that it might function in “communication, sexual selection, camouflage, or improved visual acuity … or, perhaps (it has) no function at all in some lineages.”

Whatever the function is (or is not) these amphibians are well costumed for trick-or-treating!

Bats and Cactus Flowers

Espostoa cactus. Photo by M. Weigen. Freie Univ Berlin

Flowering plants have been co-evolving with pollinating animals for 120 million years. The remarkable diversities of flower shapes and colors are profoundly important to the flowering plants as they enable the plant to attract pollinators (often immensely specific pollinating species) and direct them to the pollen bearing organs (often via a nectar reward). Very simple flowering plants  release great clouds of pollen into the air relying on the infinitesimal chance that some of the sperm bearing granules will fall on an appropriate type of flower. When plants connect with pollinators, though, the odds of successful pollen transfer go up considerably.

Many plants are pollinated by bats, and bats do not “see” plants or flowers in quite the same way as most other animals. Bats produce ultrasonic pulses that bounce off of objects in their environment. For a flower to be noticed by a bat, then, it must strongly reflect these ultrasonic waves.

A cactus in the Ecuadorian Andes (called Espostoa frutescens), though, has evolved a slightly different method of directing a searching bat to its flowers.

The flowers of this cactus are surrounded by dense systems of wooly hairs (called cephalia) which are designed to protect the flower and keep it from drying out in the cactus’ arid environment. The bat that has co-evolved to pollinate these cactus flowers (“Geoffroy’s tailless bat”) produces ultrasonic pulses in the range of 90 kHz. Instead of having flowers that reflect these ultrasound waves (thus “lighting up” the flower for the bat) the cehalia hairs surrounding the flower have evolved to be extremely absorptive of the ultrasound wave in the 90 kHz.  The flower then shows up as an obvious, “lighted” spot in the middle of a dark “bullseye!”

The Grandmother Hypothesis

In many species females have longer life spans than males. Often, these life span differences can be explained by a higher male mortality due to injuries that arise from fighting between males as they compete for females with whom they may mate or from a greater exposure of males to predators when they are protecting their mates, offspring or flock or herd.  Another way to explain these extended female life spans, though, is encapsulated in the “Grandmother hypothesis.” In human beings or in other species with extended nurturing periods of the young,  longer female life spans could be evolutionarily selected for in situations where the post-reproductive females (the “grandmothers”) contribute in some positive way to the survival of their offspring or their offspring’s offspring.

I have talked about this “grandmother hypothesis” in terms of human beings before (Signs of Summer, August 22, 2019). There was, though, an article published in Science (December 9, 2019) that discussed the importance of “grandmother” killer whales.

Orca female and calf. Photo by C. Michel. Wikimedia Commons

Killer whales (more appropriately called “orcas”) live in family based pods. Male orcas in the wild live on average for 60 to 70 years while females in the wild live on average 80 to sometimes over 100 years. In captivity these life spans are greatly shortened (average life span of a captive orca is only 14 years!). Male orcas continue to be reproductively viable all trough their life span, while female orcas go through menopause somewhere around age 40 to 45. Females, then, live with their pods as non-reproducing individuals for 50 to 60 years, and it turns out that these “grandmother” orcas are extremely important to the survival of their offspring’s offspring!

Calves without a grandmother have a four-fold greater chance of dying in the next two year period of time than calves that have a grandmother. Much of this benefit is because of food sharing, and it is especially important during times of prey (like Chinook salmon) shortages. Mother orcas tend to freely share food with their male offspring, while grandmothers freely share food with both male and female “grandchild-whales.” Whales as old as 20 years of age have been shown to have increased rates of survival when they have a living grandmother orca.

My grandmother used to make me brown sugar sandwiches on home-made bread warm and fresh out of the oven. I bet she would have given me some of her salmon, too! Thanks, Grandma!

 

Posted in Bill's Notes | Leave a comment

Signs of Spring 13: More on Butterflies (Evolution, Poisons, Rearing)

Luna moth (male). Photo by David notMD, Wikimedia Commons

(Click here to listen to an audio version of this blog!)

The evolution of moths and butterflies (the “lepidoptera”) is a topic that is constantly being revised as new evidence is found. It was once widely assumed, for example, that the present day lepidoptera arose and coevolved with the flowering plants. The first flowers show up in the fossil record 130 to 150 million years ago (MA), and most previous studies have suggested that moths came into existence around 130 MA and butterflies significantly later (around 56 MA). So, these time frames fit well into the flowering plant/lepidopteran coevolutionary model.

A few years ago (Signs of Spring 3, March 15, 2018) I talked about some findings that radically altered both the evolutionary time frames and also the vision of the ecological roles of these first lepidoptera. Fossilized lepidopteran wing scales collected from sedimentary rocks in Germany were dated back to 200 MA! This is at least 50 million years before the evolution of flowers! With no flowers from which nectar could be gathered, what were these early lepidoptera eating? It was speculated that they drank, like the very early emerging spring butterflies of today, tree saps and other available fluids.

A recent publication, though, has pushed the origin of the lepidoptera back even further.

In a paper published in the Proceedings of the National Academy of Science (November 5, 2019) a research team from the Florida Museum of Natural History used DNA sequences to reconstruct the evolutionary time line of the lepidoptera. Their data traced the origin of the earliest moths back to their divergence from a caddisfly-like, stream dwelling insect 300 MA! These first moths retained the caddisfly, gnawing mouthparts for 60 million years or so and then evolved their distinctive, fluid feeding, tubular mouthparts which they used to feed on the increasingly abundant tree saps until flowers with their nectars evolved.

These early moths, like present day moths, were all nocturnal. Butterflies, though, are active in the day and living in the sunlight has caused them to evolve their rich arrays of colors and visual patterns through which they advertise their toxicities, attract mates or camouflage themselves in their habitats. Butterflies, according to the DNA analysis, diverged from the moths 98 MA (or nearly 40 MA earlier than the previously analyzed fossil record indicated).

Comma butterfly. Photo by D. Dunford, Wikimedia Commons

Why is this earlier evolution of butterflies significant? It was once widely assumed that butterflies evolved because of intense predation pressure on the nocturnal moths by bats. The previously accepted origin date of the butterflies (56 MA) and the ages of the first bat fossils (50 MA) were close enough to support this hypothesis.  Putting the origin of the butterflies into a much more distant past, though, requires re-imagining the selection pressure for their initial emergence, and these new models return to the idea of co-evolutionary changes with flowering plants.

One hundred million years ago moths would have been relying on the wide array of flowering plants for nectar. These flowering plants, though, if they were like present day species, tend to make larger quantities of nectar during the day. Butterflies, the daylight active “moths,” possibly came into being not to avoid predators but, instead, to take advantage of this more abundant food source.

Monarch caterpillar eating milkweed. Photo by D. Sillman

A butterfly with which we are all quite familiar is the monarch. Monarchs are able to do something that is really quite extraordinary: they exclusively eat a highly poisonous plant throughout their larval (caterpillar) stages of development and are able to accumulate these plant poisons into their tissues and give themselves and the adults they turn into, significant protection against a wide range of vertebrate predators!

A team at University of California, Berkeley in a recently published paper in Nature (October 2, 2019) looked into how this remarkable system might have evolved.

They found that only three mutations were needed to develop resistance to milkweed’s cardiac glycoside poisons and to efficiently package these toxins into the butterfly’s larval and adult tissues.  These cardiac glycosides exert their toxic effects by interfering with vital sodium channels on muscle and nerve cells, so it is not surprising that two of these mutated gene loci were involved with the protein structure/shape of these sodium channels.

These genes in various combinations were identified on an array of butterflies and other insect species that live in a variety of associations with milkweed. These genes were also isolated and transferred via CRISPR into fruit flies ultimately generating a fruit fly mutant that could live on previously toxic milkweed.

Photo by D. Sillman

And, finally, an increasingly popular hobby is raising caterpillars into adult butterflies. I know several people for whom this is a lively avocation. They are also very good at it and have remarkable success ratios of adults from eggs!

In the past, I have tried to raise small invertebrates and vertebrates pursuant to a variety of experimental plans: I tried to raise earthworms (Lumbricus terrestris) to see if different phenotypes (dark pigmented versus light pigmented nightcrawlers) would breed true.  I also once tried to raise American toads (formerly Buffo americanus now Anaxyrus americanus) from eggs that I had collected from neighbor’s swimming pool. I hoped to get enough toads so that I could raise selected cohorts on different diets to see if diet affected the nature of the toxins they secrete from their parotoid glands. Anyway, my worm cultures dried up and died (the stench in my lab was awful!) and my four aquaria full of active tadpoles funneled down to a handful and then to just a single tiny toad that, in spite of its luxurious diet of mutant fruit flies (vestigial wings so they couldn’t fly away from him!), also finally expired.

Science marches on!

Anyway, I really respect and admire those gifted individuals who have the knack, the instinct and the attention to detail that enable them to raise the young of any small (or large for that matter) creature.

Monarch butterflies are a very popular species for hand raising projects. A major motivation for culturing monarchs is the addition of the reared cohort of butterflies to the monarch’s diminishing, migratory populations. A recent paper in Biology Letters (April 18, 2020) by a research team at the University of Georgia, though, challenges the efficacy of this practice.

Using very ingenious apparatuses this research team measured the muscle strength of wild caught and lab raised monarchs. They also measured the surface area of their wings and the intensity of their wing pigmentation (an overall index of health and vigor). They found that the lab raised monarchs had weaker muscles, smaller, less elongated wings and paler wing pigmentation. These captive, lab-reared monarchs were functionally different from their wild counterparts.

Tagged monarch butterfly. Photo by D. Ramsey, Wikimedia Commons

Previous studies had noted that the rates of recovery of tagged, hand-raised monarchs in their overwintering, Mexican forests were substantially lower than the recovery of tagged, wild monarchs. The conclusion was that a large percentage of the hand-raised butterflies were too weak to successfully accomplish the rigorous southern migration.

Difference between the respective stress matrices affecting the caterpillars and adult butterflies in captivity vs. the wild are thought to be the reason for these observations. Wild caterpillars face a myriad of environmental perils while they feed and grow (including predation by a variety of invertebrate and naïve vertebrate species (those vertebrates that haven’t learned that monarchs are poisonous), and death due to milkweed plant defenses). The caterpillars that survive these selection factors, then, are more vigorous and more fit than the hand-raised cohort who are raised in predator-free and relatively stress-free environments. The researchers, in fact, caution against releasing hand-raised monarchs into the wild for fear of adding weak genotypes to the breeding population. As one of the co-authors of this paper put it,   “ …. resources may be better spent on habitat conservation and fighting climate change, rather than rearing armies of monarchs.”

 

Posted in Bill's Notes | Leave a comment