Signs of Fall 6: Changing Leaves

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Orange leaves

Photo by D. Sillman

I am waiting for the leaves to fall en mass from my trees. It is an event that occurs about the same time each year (sometime after Columbus Day but before Halloween), but every year it seems late in coming. I am not sure why I am always so eager to get on with the Fall, it just means that winter is closing in on us and that the color green is going away for five months!

Leaf loss is a purely “economic” decision for a tree. Leaves are a tree’s organs for photosynthesis and energy acquisition, but leaves also lose incredible quantities of water via transpiration. In the summer many tree species (like black locusts and the cherries) balance their needs for energy (for growth, reproduction, repair, etc.) with the necessity of maintaining an acceptable water balance in their tissues and cells. In wet summers, like this year, these trees can keep all of their leaves, fix abundant energy, and transpire water without damage. In dry summers, though, the limiting factor of water availability makes the tree give up some of its photosynthetic potential in order to maintain its water balance. In these dry years “Fall” actually starts in June or July!

With the approaching winter the leaves for all deciduous trees are shed primarily to help the trees to withstand the incredibly 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 the cellular  structures of the leaves that they would be incapable of any future photosynthesis.

Photo by D. Sillman

When 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 petiole 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, and, so, sugar levels rise in the leaf and nutrient levels fall. The lack of nutrients causes the leaf to stop synthesizing new chlorophyll molecules. Chlorophyll is, of course, the functional pigment of photosynthesis and also the pigment that gives plants their characteristic green color. Initial cessation of chlorophyll production makes the leaves appear a bit paler and less intensely green than they were during the height of summer. Continued loss of the chlorophyll then starts to unmask the other pigments (the “accessory” pigments of photosynthesis: the carotinoids and xanthophylls) that had been present in the leaves all summer long. As these pigments are “revealed” the leaves then “turn” orange (from the carotinoids) or yellow (from the xanthophylls) before they finally fall. The accumulation of the sugars in the leaves also has an effect on eventual leaf color. These sugars stimulate the synthesis of anthocyanin pigments in the leaf. These pigments generate purple or bright red colors in the leaf and are thought to possibly protect the leaf (and particularly next year’s delicate leaf buds) from insect damage.

Photo by D. Sillman

The deciduous trees in our area are beginning to turn their autumnal colors. The breakdown of the chlorophyll and the revealing of the accessory pigments is inevitable in our climate zone. In some years, though, the intensity of the reveled colors is much more extreme than in other years. The weather patterns of the fall and of the preceding spring and summer all contribute to the magnitude of the final color response.

Good, healthy abundant leaves are favored if the previous spring had adequate rainfall. A normal to wet summer insures that a large number of leaves will persist intact through their active photosynthetic seasons. Warm, sunny autumn days combined with cool but not freezing autumn nights will maximize sugar production and anthocyanin synthesis in the leaves. These accumulating anthocyanins then give the leaves their brilliant red and crimson colors that are so important in defining a “good” color year in the forest!

The way this year is working out, we should have some very spectacular colors around us, and that is almost everyone’s favorite Sign of Fall!

Photo by D. Sillman

After the leaves fall from my trees, I usually rake them up into several large, strategically located piles around my yard and leave them to nourish the worms and beetles and other invertebrates that will shred and grind them up into food for fungi and bacteria. In the old days my kids and I would jump in the piles and further accelerate their fragmentation. Now I just rely on the worms to do the job with less noise and vigor. Through the next spring and summer birds (especially the robins and the cardinals) peck at and dig around in the leaf piles looking for insect larvae and earthworms. These leaf piles are a great source of nutrition for these hunters and gleaners. By the time the next fall rolls around, the piles are remarkably reduced in size and are ready to be renewed by freshly raked up leaves. One pile down in my orchard was kept in this yearly equilibrium for over twenty years. I eventually dug up the rich, humus that accumulated at the bottom of the pile and added it to the soil of my tomato patch.

In a forest, the fallen leaves spread out in a thin layer over a broad area. Earthworms start working on these leaves right away, pulling them into their middens and burrows, grinding them up with their muscular mouth-parts and gizzards, mixing them up with ingested soil, and defecating them out in nutrient rich, erosion resistant pellets. In soils without earthworms, numerous arthropods of many sizes begin to slowly chew away the leaf materials making a fine powder of organic residues enriched with bacteria. Both the worms and the arthropods are setting the table for the bacteria and fungi that then steadily work away at the less resistant molecules in the leaves. Like in my leaf piles, by the time the next fall comes around what’s left of the old leaves serves as a base for the new and the decomposition process grinds on.

So, enjoy the coming events of the Fall and make sure you use your leaves for the biological health of your yard!


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Signs of Fall 5: Roundworms in the Park

Toxocara canis (nematode) adults. Photo by A. Walker. Wikimedia Commons

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“Roundworm” is another name for “nematode.” When you consider that every pinch of topsoil contains dozens to hundreds of individual nematodes, and that every living vertebrate and invertebrate animal and also every plant contains hundreds to thousands to many millions of nematodes, it is very easy to see why many biologists rank nematodes as the most numerous animal on Earth (only the tiny crustaceans that make up the oceanic clouds of “krill” come close to the numerical abundance of free-living and parasitic nematodes).

One of my agronomy professors at Ohio State once said that if all of the mineral and humic components of soil were magically removed you could still see the outline and depth of the original soil because of all of the nematodes. You could even walk around on them, he added, but they might be a bit slippery! (That may be the only joke ever told in one of my agronomy classes!)

So, we all agree that there are a lot of nematodes on Earth!

Some of the nematode parasites found in vertebrates live in the food-packed section of the digestive system called the small intestine. These “intestinal roundworms” feed on the digesting food flowing through this tubular organ and then grow and reproduce prolifically making hundreds of thousands of eggs per day! Sometimes these nematodes live in equilibrium with their host, sometimes they grow out of control and inhibit digestion and absorption of nutrients from the small intestine. Sometimes they can even cause serious blockages of this part of the digestive tract!

A basic concept in parasitology involves the distinction between a “definitive host” and a “non-definitive host.” A parasite can only reach adulthood and be able to reproduce inside the body of one of its “definitive hosts.” In a “non-definitive host” (which could be almost any other type of animal that has inadvertently picked up some other species’ definitive parasite), the parasite often gets stalled in some pre-adult, “larval” stage and is never able to finish its life cycle. These non-definitive host infections, though, may have some serious health impacts on the host organism!

Photo by M. Hamilton

Dogs and cats are the definitive hosts for some species of intestinal round worms in genus Toxocara (the very logically named species are Toxocara canis and Toxocara cati).  Part of the regular veterinary care we give our pet dogs and cats involves examination of the animal’s feces for Toxocara eggs and the administration of some very effective treatments to both eliminate any Toxocara that might be living in the pet’s intestine and prevent their re-occurrence. Puppies are often loaded with Toxocara nematodes. The newest addition to the Colorado branch of my extended family (“Gedi”) is pictured to the left. He has had to have numerous treatments before his “birth-load” of nematodes came under control!

The good news is, then, that most well cared for dogs and cats do not have intestinal nematodes and are not depositing nematode eggs in the spots where they have voided their feces. The bad news is, though, stray dogs and cats that do not receive these regular nematode assessments and treatments do often have active Toxocara populations in their intestines, and these animals shed an incredible number of potentially infectious, microscopic eggs each time they void their feces.

Humans can be a “non-definitive host” for either dog or cat Toxocara nematodes. This of course means that the nematodes are not able to reproduce inside of a person, but the larval forms of the roundworms can impact a number of internal organ systems and, occasionally, do some considerable damage to a human host.

Toxocara embryonated eggs. Photo by Flukeman, Wikimedia Commons

The Toxocara eggs in an infected animal’s feces must mature out in the soil/feces environment for two to four weeks before they are potentially infectious. The nematode embryo in the fertilized eggs needs to develop to a point that it is able to actively move about inside of whatever host it enters. Once the egg/embryo is in its infectious life form, though, it may be able to persist in the soil/feces external environment for up to a year. Considerable numbers of these infectious life stages, then, can accumulate in a soil system that regularly receives contaminated dog or cat feces.

Most often people are exposed to these nematode eggs via the inadvertent ingestion of contaminated soil. Unwashed or poorly washed hands are the most common infection pathway. Flies that have walked about on contaminated surfaces may also spread the nematode eggs to human foods. Children because of poor hygiene habits and their tendency to play in sand boxes and dirt piles of their yards and playgrounds are frequently exposed to infectious Toxocara eggs. These eggs and their infectious larval life forms can also enter a body via cuts or abrasions in the skin and via the ingestion of uncooked or poorly cooked meats or organs (especially livers) of other non-definitive host species (rabbits, chickens, snails, earthworms, etc.). Cultures with traditions of consuming uncooked internal organs or raw, soil dwelling invertebrates may have very high levels of Toxocara infections.

Most human Toxocara infections are short-lived and mild (general fever, malaise etc.). Sometimes, though, Toxocara larvae can move about inside a person’s body and accumulate in the liver, lungs or eyes causing significant, and very persistent inflammatory damage. There is also some evidence that higher brain development in children and intelligence can be negatively affected by chronic Toxocara infections.

Anywhere between five and ten percent of the population of the United States carry antibodies to Toxocara nematodes (different sources cite different overall numbers). The presence of these antibodies means that these individuals have had a Toxocara infection sometime in their past. According to the Center for Disease Control (CDC) poor and minority populations have a significantly higher Toxocara infection rate than the rest of U.S. population.

Photo by Bru-no. PIxabay

A recent study mentioned in a New York Times article about the ubiquity and potential impacts of Toxocara infections in New York (“The Parasite on the Playground,” January 16, 2018) found that 75% of the playgrounds in the lower socio-economic sections of the city tested positively for infectious Toxocara eggs while no eggs were found in playgrounds located in the more affluent sections of the city. The vigorous control of stray dogs and the enforcement of dog waste cleanup and removal in the more affluent neighborhoods are two logical reasons for this discrepancy.

In all of this information are a couple of key points for all pet owners to recognize: 1. Make sure your pet is free of intestinal nematodes, and 2. Pick up and dispose of their feces as quickly as possible (remember, the eggs in the feces take several week to grow into their infectious state!).

So, enjoy every minute with your dog and cat, but take the time to be a biologically aware owner!





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Signs of Fall 4: Giant Hogweed!

Photo by D. Sillman

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Hiking on the woodland trails or across the old fields of Harrison Hills Park (or almost anywhere, for that matter) you see a familiar array of plants. It is quite startling to realize that so many these plants are, in fact, alien species carried to North America sometimes intentionally and sometimes unintentionally by people.

Garlic mustard, Japanese knotweed, barberry (both European and Japanese), honeysuckle (Amur and Japanese and Tartarian), multiflora rose, poison hemlock, mile a minute vine, privet (four different kinds!), tree of heaven, and common mugwort make up a substantial proportion of the plants across the park (and our county and our state!). All of these species are non-native and all have been classified as, and are very recognizable as, invasive species.

But there are also many species we value on the alien, invasive list including butterfly bush, dame’s rocket, orange daylily, coltsfoot, and chicory.  The Native Plant Center even lists forsythia as an exotic invasive species. How could you have watched swarms of monarch and swallowtail butterflies gathering nectar from the park’s butterfly bushes and considered them alien invasive plant? And the sight of coltsfoot and then forsythia blooming in the early spring, and then dame’s rocket in June, and the orange daylilies and the blue-flowered chicory in July seem like true signs of the passing seasons rather than visual evidence of an alien invasion.

We are, according to Charles Mann, living in the Homogeocene! People are moving not only themselves but also wild and domesticated plants around the world so rapidly that the vegetative ecosystems all over the Earth are becoming dominated by the same hardy, generalist species. Travel to Central Europe or to South America or Africa or Asia and you find similar arrays of invasive species alongside all of the pathways through the untended and also the cultivated regions.

Deborah made a set of webpages in which she described the flowering plants of Harrison Hills Park. Of the 161 plants that she has observed in the park, 52 (32%) are alien species. The park is a good place to get a glimpse of the Homogeocene!

Leaf of giant hogweed. Photo by D. Harper, Wikimedia Commons

Every once and a while, though, some new alien invasive plant comes to popular attention often because of some massively exaggerated feature of its anatomy or its ecology. The invasive of this past summer is giant hogweed (Heracleum mantegazzianum).

I first read about giant hogweed on an information posting on I was checking on the upcoming day’s weather and I saw a headline at the bottom on the page, “Horror Plant Spreads in US!” The story went on to describe giant hogweed as a member of the carrot family that can grow 14 feet tall and produce a sap that can interact with sunlight and cause third degree burns on unfortunate people who have come in contact with it. The plant shades out native plant species (anything under 14 feet tall, anyway!) and has been found in Virginia, Maine, New York, New Jersey, Massachusetts, Connecticut, Pennsylvania, North Carolina and parts of the Pacific Northwest.

After reading that article, I was glad that I had never run into giant hogweed. The next day, though, I got an email from one of our bluebird volunteers at Harrison Hills Park relaying a request from an acquaintance who thought that they had seen giant hogweed in two locations of the park! Deborah and I were on our way to Ann Arbor for a few days but promised that we would check out the park locations when we got back.

First, though, we went to Internet for more information!

One point of some reassurance was that although Pennsylvania is on the hogweed-positive list, hogweed has only actually been confirmed, according to the very frequently updated “Early Detection and Distribution Mapping System of Invasive Plants,” in two of its counties: Erie and Mercer. Both these counties are quite far away from northern Allegheny County and Harrison Hills Park. Giant hogweed was, though, quite extensively reported from New York State and northern New Jersey, so it seemed to closing in on the borders of Pennsylvania.

Flowers of giant hogweed. Photo by M. Pixel

The second important piece of information was that although a 14 foot tall giant hogweed plant should be remarkably distinctive, there were a number of plant species that were frequently confused with it. Three plants mentioned in the New York State Department of Environmental Conservation “Giant Hogweed Identification” website are cow parsnip, wild parsnip and poison hemlock, and all three of these potential “lookalikes” are found at Harrison Hills Park.  None of these three giant hogweed imposters, though, really manifest the essential features of the plant. Giant hogweed stands between 7 and 14 feet tall. It has huge (2.5 feet across), white flowers with 50 to 150 rays organized into a broad umbrella shape. The leaves are also huge (five feet wide) and deeply incised and lobed. It’s stems are green with spatters of purple and lots of coarse white hairs. Cow parsnip is the closest giant hogweed mimic but its leaves and its flowers are half as large and its flowers are flat rather than domed up like an umbrella. Also its stem are green with no purple splotches.

So, the day after we returned from Ann Arbor, we went up to Harrison Hills to look for giant hogweed. On our walk about the suspected areas we found extensive stands of poison hemlock and wingstem (a tall, native “weed”) but no giant hogweed (and also no cow parsnip which we were assuming to be the stimulus for the hogweed report). Turning a corner around a large pile of plant debris, though, we came face to face with a plant that looked so huge and so out-of-place and so alien that it had to be the hogweed wanna-be.

Photo by D. Sillman

The plant was growing in a cluster of five or six stems. The stems were very woody and not the green, purple-blotchy, hairy stems one would expect of giant hogweed. The leaves were very large (about 4 feet long and four feet wide) but were not deeply incised or lobed (as one would expect from giant hogweed). This was something unusual, but it was not giant hogweed. It turns out that this plant was another potentially nasty, exotic invasive species called the princess tree or, sometimes, Royal Paulownia (Paulownia tomentoas).

The princess tree is a native of central and western China and was brought to this country (and many countries in Europe) as an ornamental or through the accidental distribution of its seeds (which were used in the days before Styrofoam peanuts as packing materials). It is extremely fast growing, prolific in its production of seeds, and able to tolerate a wide range of environmental conditions. It would be a tree valued for its appearance and vigor except for its tendency to rapidly spread and engulf any area into which it is introduced.

We passed along our observations but don’t expect that the princess trees will be cut down. We will keep an eye on them in coming years!

So, we went on an invasive plant hunt and we found one! It just happened not to be the one we were looking for!




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Signs of Fall 3: Cavity Nesting Team, Year Four Completed

Photo by D. Sillman

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The Cavity Nesting Team has completed its 2018 observation season up at Harrison Hills Park in northern Allegheny County. This year we had twenty-nine nesting boxes scattered across the park. Our 2018 monitoring began at the end of March and ended in late August. Data from our three previous study years have helped us to learn how to optimally locate nesting boxes for bluebirds, and this year’s record number of nesting boxes (19) utilized by bluebirds shows that our criteria for box placements were ecologically sound.

The ten volunteers who make up the Cavity Nesting Team (see Signs of Summer 6, July 12, 2018) checked every box in the park at least once a week and recorded the presence of  and types of nests, numbers and types of eggs, numbers of nestlings, and numbers of fledglings . A total of 540 observations were recorded in our on-line spread sheet.

We saw our first bluebird nest on April 19 in nesting Box Q near the park’s Environmental Learning Center, and the first eggs were seen in that nest a week and a half later (April 28). Two weeks later (May 14) these eggs had hatched into nestlings and by then a large number of other boxes throughout the park were being utilized by nesting bluebirds. Our last nest was also built in Box Q (on July24) and four eggs were observed on July 29. These eggs all hatched and developed into young bluebirds that fledged on August 25.

The bluebirds at Harrison Hills nest and reproduce in two distinct time intervals (one in early summer (May/June) and the other in late summer (July/August)). In our previous years’ studies the early summer reproducing cohort produces two thirds of the eggs and two thirds of the fledglings for the season, and this year was no exception (69% of all eggs were laid and 63% of the bluebird fledglings were produced in the early summer of 2018).

K. Thomas, Public Domain

We observed a record number of bluebird nests in 2018 (23 nests), but also had a record number of bluebird nests that had no eggs (six) and ones that had a high degree (50% or more) of egg mortality (also six). The impacts of the eggless nests and large number of lost or undeveloped eggs reduced the overall egg production for the season to the second lowest total of the past four years (only 67 eggs) and reduced the total number of bluebird fledges to the lowest number we have observed over the four years of our study (only 46). Also, the early summer “success rate” for our the bluebird eggs (percentage of eggs that fully developed into fledges) was the lowest we have observed in our study (only 63%).

Why did we see an apparent breakdown in the nesting and fledging success of our bluebirds? The weather this summer was very different from any of the previous years. We had record high temperatures in May (average daily temperature in May was seven degree F above historical averages) and extremely high rainfall in the months of April (148% over historical average), June (193% over historical average) and August (152% over historical average). We are not sure if these unusual weather conditions contributed to increased activity of nest parasites or predators or if they might have directly stressed either the adult birds or the nestlings.

Our 2018 bluebird observations, then, had negative and also some positive components. The reduced egg and fledgling numbers and lowered egg to fledgling “success percentages” were disturbing. The Team will continue to look over the data to try to come up with some hypotheses to explain this observations. Our large number of boxes that had bluebird nests, though, and the park-wide distribution of these bluebird-utilized boxes indicate the ecological soundness of box locations and the quality of the entire park as a habitat for nesting bluebirds.

K. Thomas, Public Domain

Four nesting boxes had tree swallow nests and 20 eggs were observed. All of these nesting boxes were located in the north end of the park. None of these swallow-utilized boxes, though, were located near the large pond in the south end of the park. In 2015, three nesting boxes near the pond had had tree swallow nests, and we considered these boxes to be optimal for swallows because of the proximity of abundant flying insects (dragonflies etc.) over and around the pond. None of these pond-area nesting boxes, though, have subsequently been used by tree swallows! We are still uncertain why the swallows are avoiding these seemingly optimal nesting sites!

The tree swallow eggs were laid in the expected single, “mid-summer” time period that followed the initial blue bird reproductive cycle but preceded the bluebirds’ later “late summer” second reproductive event. This year’s tree swallow egg total was very comparable to our 2015 observations and was a significant rebound from the very low tree swallow eggs production of 2016 and 2017. We have speculated that the dry summers of 2016 and 2017 inhibited the emergence of the aquatic insects upon which the swallows rely to feed their nestlings. Tree swallows are known to be resource-dependent reproducers. The very wet summer of 2018 must have generated an abundant food base for the swallows, and they responded with a solid reproductive effort. Further, all twenty tree swallow eggs resulted in viable nestlings, and all twenty nestlings successfully fledged. This was the first 100% success percentage that we have recorded in our nesting box studies!

Photo by dfaulder, Wikimedia Commons

House wrens are a native bird species and a common cavity nester. They are also, though, very aggressive and destructive of the eggs, nestlings and fledglings of many other cavity nesting birds (including bluebirds). For that reason, we set up some protocols this year to try to discourage house wren reproduction. In past years we have observed some bluebird and tree swallow egg and nestling destruction by invading house wrens.  This year, one of the wren nests displaced a freshly built chickadee nest. The wrens usurped the nest from the chickadees and laid their eggs in the formed nest (it is not known if the chickadees had laid eggs or if chickadee nestlings had hatched in the nest, but if they had, they were destroyed by the wrens).

Nine nesting boxes broadly distributed across the park had house wren nests and thirteen eggs were observed. Of these thirteen eggs, though, only four developed into fledglings (a 31% success percentage). In past years, the house wrens nested and reproduced concurrent with the early bluebird nesting cycle (“early summer”).This year’s wren reproduction, though, occurred later in the season (corresponding more to the middle summer reproduction cycle of the tree swallows). Possibly this delay was due to both the Team’s strategic interference with the wrens’ “dummy” display nests (in an attempt to discourage wren reproduction) and also to our moving a number of nesting boxes away from the park maintenance area (an hypothesized habitat refuge for the wrens).

We are satisfied with our house wren experiment. Distracting the male wrens and forcing them to continuously rebuild their display nests may have been sufficient to reduce their potentially explosive reproductive potential.

House sparrow nestlings. Photo by P. Kopnicky

Also in 2018, for the first time in our cavity nesting box study, we have observed house sparrows (“English sparrows”) in one of our nesting boxes. These alien, invasive birds are very destructive (they invade established bluebird and tree swallow nests and destroy eggs and kill both nestlings and adults). The location of the park well removed from human habitations has insulated us from these birds, but here in the fourth year of our study they have finally shown up. Four eggs developed into four fledglings in one of the boxes near the Environmental Learning Center. We think that the house sparrow nest was built on a bluebird nest and possibly even on top of the dead bodies of some bluebird nestlings or adults. Since house sparrows are not native species, we were well in our legal rights to dispose of their eggs and even their nestlings, but none of us had the heart to do so. We hope that the fledged house sparrows will fly off to a habitat more suited to their needs (there is a McDonald’s and a Burger King not all that far away in Natrona Heights). We will, though, keep an eye out for them here in the park!

Stay tuned for Cavity Nesting Team 2019! We will have more ideas to test and more beautiful birds to encourage and count!




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Signs of Fall 2: Observations

Photo by srinivasaroab, Pixabay

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It was raining quite hard tho other morning. In fact it had been raining hard for the three days before. One day we got almost four inches of rain! The remnants of Tropical Storm Gordon fed into a midwestern cold front and set up a conveyer belt of water delivery to the East Coast. Temperatures have fallen to “autumn” levels, too. I have gotten out my sweatpants and long sleeved shirts and am making an extra cup of coffee in the breakfast pot to help counterbalance the cold of the morning.

This summer I moved most of my birdfeeders to the side yard so that we could see them from our new sunroom. I still have, though, the thistle feeder out front hanging from a branch of the lilac bush. The goldfinches and house finches have been emptying out the thistle almost every day, and mourning doves feed on the spillage that gathers under the branches of the lilac.

I also still toss a couple of handfuls of peanuts out front every morning for the crows. They won’t come into the confined space of the back yard and used to not even come into the front before I took down the yard fence: they need open flyways for their quick escapes! The crows watch me from the surrounding tree tops and excitedly caw when they see the peanut bag. When I go back onto the porch they immediately swoop down into the yard, gobble down their breakfast, and fly off to get on with the rest of their day.

Photo by D. Sillman

The crows wait until about nine o’clockfor their breakfast. After that, if I put out any peanuts, the shells will just lay there on the grass for hours barely touched. A few cardinals and even one or two chickadees drop in to pick up single peanuts at a time. The cardinals eat them on the spot, although they seem quite nervous eating out in the open, potential-crow space. The chickadees, though, fly their peanuts over to the sheltered branches of the arbor vitae and laboriously peck at the shells until they can get to the nut inside.

Late this morning in a brief lull in the rain, I went out and filled the thistle feeder. Under the feeder, next to what was left of the peanut shells, were the remains (feathers and some bones) of a mourning dove. The dove must have been eating the fallen thistle when it was attacked by the sharp-shinned hawk that regularly patrols our yard. In the hour or so between my putting out the crow-peanuts and returning with the thistle, the hawk had killed the dove and consumed most of it.

There is another burst of fledglings coming into our feeders! The house finches and goldfinches have large cohorts of late summer offspring. The cardinals have also successfully launched another brood. This might be the fourth cardinal clutch of the season! The finches alternate between the thistle feeders and the sunflower feeders, but the cardinals are at the sunflower feeders almost all day long. The fledges take a few days to get the self-feeding routine down, but then they start to act like mature birds (except when they see their parents, and then they flutter their wings and beg shamelessly for food).

Photo by D. Sillman

The male hummingbirds have left our yard. They have begun their fall migration southward. The females and the fledges, though, are still here. I watched one fledge methodically hunting for insects up and down the branches of the scarlet oak and the arbor vitae out in my back yard. There have been lots of small gnats and mosquitoes around (all the rain has made great conditions for tiny dipterans), and the hummingbirds must be feasting on them!

I haven’t seen any monarchs for several days. I hope that the migration cohort has gotten a good start on their long trek to Mexico. Observations here in Western Pennsylvania this summer have been very positive. We have seen more monarch butterflies than in any recent year, and more caterpillars and chrysalises, too. It will be interesting to see what the winter monarch hibernation count is this year in the forests of Michoacan and Mexico.

The other morning a small flock of Canada geese flew low over our house. They were partly hidden in the morning fog, but honked loudly as they went past in their distinctive “vee” formation. Deborah was out walking Izzy at the time and said that she could feel the turbulence of the geese’s wings as they flew over her. Izzy, of course, had no idea of what was going on!

Photo by Neonorange Wikimedia Commons

Earlier this spring Patrick Kopnicky and Paul Hess talked about the Canada geese (Branta canadensis) of Pennsylvania. In the early part of the Twentieth Century global Canada geese populations reached dangerously low levels due to uncontrolled hunting and habitat loss, and very few Canada geese were found in or passed through Pennsylvania. The regulation of their hunting and the establishment of wildlife refuges around the Chesapeake Bay and on the barrier islands off of the Delmarva Peninsula helped the migrating subspecies of the Canada geese begin their recovery. The Pennsylvania Game Commission in the 1930’s also brought in a small population of Canada geese and released them at Lake Pymatuning. These introduced geese, though, were the “maxima” subspecies  of Branta canadensis.  These are the larger version of the Canada goose that are, very significantly, non-migratory! Prior to 1935 there were no non-migratory, resident Canada geese in Pennsylvania, now  there are over 240,000 of them, and they are found  in every county in Pennsylvania. Many of these geese create great problems for the ponds and parks in which they reside.

The geese flying through the morning fog, then, created an almost archetypal symbol of the coming Fall. They suggested the first phases of the great Fall migration to the south.  These geese were, though, probably just some resident Northmoreland Park geese out for a little exercise before breakfast! I bet they were back home before I had my second cup of coffee!





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Signs of Fall 1: Three Trees in Colorado

Photo by M. Hamilton

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Deborah and I went out to Colorado a few weeks ago to visit our daughter and her husband in Greeley. Our son and his girlfriend also joined us, and we all had a great time complete with a day trip to some mountain hiking trails that we had explored 18 years ago on a family vacation. I kept my eyes open for some good blog topics, but other than a lake full of white, American pelicans and some unbelievable hail storms (3 or 4 inches of hail-ice on the road! Miles of sublimating ice-fog making roads almost impassable! Massive defoliation of trees (including a poor, indoor fig tree unintentionally left out on an uncovered patio during the storm!) ), everything was pretty “normal.” So, when in doubt, talk about trees!

Our home in Pennsylvania is a place of trees, the translation of the state’s name to “Penn’s Woods” tells you that. Flying over Pennsylvania or driving along its Interstate highways or country roads emphasizes the abundance and ubiquity of trees! Forests are everywhere! The original forests of the state represented the first in a long line of natural resources that the various colonial and then state governments of Pennsylvania gave away to economic interests. Only 5% of the state’s original forests escaped repeated logging over the past two hundred-plus years, and most of that 5% is in small, acre sized patches scattered across the commonwealth. The abundance of rainfall in Pennsylvania (average 41 inches/year) and the deep, fertile soils, and an abundance of hearty tree species have helped the state’s forests repeatedly recover from the destruction of clearcutting and mismanagement.

Photo by Colorado State Forest Service

Colorado, in contrast, does not seem to be a place extremely conducive to trees. Colorado is arid (15 inches of rain a year on average) with very uneven rainfall. The entire eastern half of the state gets 10 to 12 inches of rain per year while places in the mountains may get 35 to 40 inches of precipitation per year. You find trees in the places where water is available: along rivers and lakes, in sheltered valleys, and up on mountain slopes. Colorado cities also have lots of trees but only because of direct human intervention. The rest of the state is brush and rangeland (except where they are growing wheat, corn, hay, beans or sugar beets, and there irrigation is typically required to sustain the annual abundance of the biomass of the crop plants).

So the trees of Colorado must be trees of the mountains and trees of riversides.

Photo by M. Pixel

The state tree of Colorado is the Colorado blue spruce (Picea pungens). We saw some impressive blue spruces when we were up in Rocky Mountain National Park. Most of these trees were scattered out among some stately Ponderosa pines or bordered by dense stands of lodgepole pines or quaking aspens.   The blue spruces thrive in the dry, short summers and cold, long winters of the Rockies. Colorado blue spruce has a very limited natural range, but because of its ability to grow in a wide range of environmental variables it has been planted as an ornamental tree far outside of its natural distribution! You can find blue spruces in urban and suburban landscapes all across North America and Europe. This past summer, for example, I was amazed to see blue spruces all over Prague, Czech Republic! The blue spruce is also one of the most commonly planted trees in Pennsylvania! Unfortunately,  the long term health of many of these planted blue spruces is not very good. The long, hot, wet summers and short winters of these non-mountain climate zones have allowed all sorts of fungal diseases to take down many of the blue spruces (See Signs of Summer 12, August  3, 2017).

Blue spruces are not a terribly important timber tree. Its wood is light and full of knots. It also does not generate a great abundance of food for either seed eaters or browsers. It does provide, however, good cover for birds and many small mammal species. This tree is dominantly valued for its appearance and regularly makes top five or top ten lists of importance primarily because of its pleasing color and overall shape.

Photo by J. Westfall, NPS

Quaking aspens (Populous tremuloides) are the definitive hardwood tree of the mountains of the Middle Rockies. Quaking aspens have the broadest natural distribution of any tree in North America. Northern Pennsylvania is even included in the vast, continent-wide distribution of this species! It is a quick growing and relatively short-lived tree (100 to 150 years) that becomes quickly established after a fire. Quaking aspens reproduce by root sprouting and often form dense, clonal groves. They also produce air-transported, fluffy seeds that blanket the downwind areas from the mature aspen groves, although seed reproduction is not nearly as important to the species as root sprouting. When you see a stand of aspens it is possible that you are really looking at a single organism! The trees are not only genetic clones but are also highly interconnected via their roots. In southern Utah there is a 100 acre grove of quaking aspens that are one highly interconnected entity. This multi-tree organism weighs 14 million pounds and is estimated to be 80,000 years old!

Aspen groves are usually generated by fires. The quick growing aspens send up root suckers after a fire and assume a pioneering role for the successional forest sequence. It is interesting that aspen forests themselves are somewhat resistant to fires: the trees’ moist, green leaves and thick twigs resist burning, but if a fire does get established in an aspen grove the above ground trees are likely to be destroyed.

Under the aspens the slower growing pines and spruces are sheltered and protected. The deciduous nature of the aspens means that its forest floor receives more sunlight than a coniferous forest floor especially in the early spring. This allows a very vigorous growth of wildflowers and herbaceous plants in the aspen groves. Aspens forests are great places to look for wildflowers!  Eventually, unless there is another fire (an increasingly likely event in our dry western ecosystems!) the conifers will grow up through the crowns of the aspens and shade them out

Public Domain

Along every river or creek and flanking every lake or reservoir are plains cottonwood trees (Populus deltoides). These cottonwoods are great, lumpy gray-barked trees of sometimes substantial girth that often rise up to 100 feet in height. Cottonwoods have thick, spreading branches that generate much needed shade and cover for a wide range of birds and mammals in the sun drenched plains of Colorado. The cottonwood trees release their eponymous “cotton” seeds in June generating snowdrifts of tumbling cotton fuzz for many miles around a stand of trees. The thick, deeply furrowed bark is resistant to fire and drought and the trees, which only live 80 to 100 years, can grow six feet in height a year in their early years of their lives. Cottonwoods often mark the edges of the scattered rivers and creeks that cross the dry high plains and were a welcome sight to early settlers announcing the presence of much needed water.

There are fifty native tree species in Colorado. I plan to be visiting the state rather frequently over the coming years. Watch for more posts, I’m just getting started!




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Signs of Summer 13: Electric Spiders!

Fishing spider. Photo by D. Sillman

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(I want to thank Robert Steffes who passed along a recent Atlantic Monthly article about the electrical nature of spider’s webs. That article led to the development of this post).

Deborah and I love spiders. We have a significant community of them living in our house, and we take care to see that as little harm comes to them as possible. Our basement, in particular, is a rich habitat for a variety of types of spiders.

Pholcid spider> Photo by D. Sillman

Pholcid spiders (also called “cellar spiders”) are numerically the most abundant in our house. We have clusters of them in every dark corner of the basement and in most of the ceiling corners of the upstairs rooms. Pholcid spiders are thin, delicate looking, long-legged spiders that make webs that look like jumbled messes of silky threads. Typically, they hang upside down under their web and wait for some insect (house flies, gnats, mosquitoes, stink bugs, etc.) to get entangled in the chaos of the silk. Their webs are not sticky but are so complex in structure that an arriving insect has difficulty extracting itself before the spider gets over to it to deliver a bite of paralyzing venom. The spider then pumps enzymes into the dead or dying prey and sucks out its digesting body fluids. When the spider is finished, it disentangles the dead insect from its web and lets it fall to the ground. Under a pholcid spider’s web, then, is a dry pile of insect carcasses upon which it has fed.

If you blow on a pholcid spiders web you can trigger an energetic threat response. The spider will start vigorously shaking the web in an attempt to get whatever might be disturbing it to back off. This behavior has led to one of the many common names for the pholcid spider: the vibrating spider.

Pholcids are not terribly particular about their types of prey. They often eat each other and will attempt to entangle and disable almost anything that gets caught in its web. I have seen pholcids go after large beetles and even bumblebees. Sometimes the large prey individual gets away, sometimes it does not.

I could go on about my basement spiders, but I have spent some time doing that already (see Signs of Spring 12 May 14, 2015). Lets talk about some recent research concerning the spider silk fibers of their webs.

Photo by VA State Park Staff, Wikimedia Commons

Spider silk, of course, is made of up proteins. Proteins tend to have very significant negative charge because of the predominance of acidic amino acid residues in their polypeptide chains. Five years ago, in a research paper published in Scientific Reports, a group at the University of California-Berkeley determined that these negative charges inherent in spider silk were an important factor in the ability of a spider’s web to capture insects. When an insect flies, its wings not only generate lift and linear direction, but they also generate significant electrical charges. To be specific, the beating wings make the flying insect quite positively charged. When a positively charged insect flies near a negatively charged spider web the attraction between these opposite charges pulls the web strands toward the insect. This interaction also, then, pulls the insect toward the web. Upon contact with the web, even if, like in the pholcid webs described above, there is no sticky mucopolysaccharides coating the silk, the insect is at least slightly stuck on the spider’s webbing due to this electrostatic attraction. For many insect-spider web interactions this electrostatic adherence gives the spider sufficient time to reach the captured insect, wrap it in more silk and deliver its venomous bite. So a spider web, because of its electrical nature, has an extended active space around it that draws flying prey into its entangling threads.

Spider attempting to balloon. Photo by Sarefo, Wikimedia Commons

There is another behavior in spiders that has had a simple, but unsatisfying explanation for many years:  the phenomenon called “ballooning.” When a spider balloons it typically climbs up on some surrounding vegetation and then raises itself up on its extended legs (a behavior called “tip-toeing”). It then lifts its abdomen into the air and releases a long strand of spider silk. The silk rises in the wind and then drags the spider off of its perch and up into the air. Ballooning is an excellent way for densely crowded spiders to disperse in order to find potentially more conducive habitats. It is also an excellent way for a spider to escape from a predator. It is an amazingly efficient transport system over short and also over long distances. Spiders have been found far out at sea (Charles Darwin famously found hundreds of ballooning spiders covering the lines of his ship the Beagle sixty miles off of the shore of Argentina). Ballooning spiders can travel over a thousand miles and have been collected two and a half miles up into the atmosphere!

The accepted explanation for this ballooning behavior was that the spiders simply sensed an adequately robust wind and then released their silk sails and took off. This ignored, however, the observation that spiders could balloon even when there was no wind at all! Some new research adds some continuity and also some complexity to the spider flying system.

Researchers at the University of Bristol have determined that spiders can sense the Earth’s electrical fields. Tiny hair-like structures on their feet (called “trichobothria”) bend and deform in response to changes in electrical fields surrounding them. Further, the Earth’s atmosphere is positively charged in contrast to the surface of the Earth (and all of the plants and animals touching the surface) which tends to be negatively charged. On stormy days this charge separation can generate extremely powerful electrical currents (and bursts of electrical discharges (lightning)) but even on clear, calm days there is a substantial voltage generated as one rises up from the Earth’s surface.  When a spider releases its ballooning silk, its negative charge is attracted to the positively charged atmosphere, and it is this electrostatic attraction that generates the lift for the spider’s flight.

In the experiments at Bristol spiders were placed in closed containers. When a electric field was generated around the containers the spiders “tip-toed,” ejected ballooning silk, and even lifted off of the floor of their containers even though there was no wind at all in the laboratory. Their ballooning stopped when the electrical fields were shut off.

Electric spiders! Pulling in positively charged, flying insects to their webs! Pulling themselves up into the charged atmosphere to catch a breeze to take them almost anywhere on Earth! I need to tell my basement spiders about all of this!






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Signs of Summer 12: Biocontrol of Insects

White footed mouse. D.G.E. Roberton, Wikimedia Commons

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About a year ago (Signs of Spring 13, May 13, 2017) I wrote about the proposed use of the CRISPR gene editing system and a “gene drive” replication amplification system to help control Lyme disease (by eliminating the critical intermediate host in the Lyme disease cycle, the white-footed mouse) and malaria (by altering the genes of the Anopheles mosquito vector that transmits the Plasmodium parasite to make the physiology of the mosquito inhospitable or even toxic for the Plasmodium organism).

CRISPR, you may remember, is a technology that employs specifically engineered RNA sequences and a protein that cuts (and pastes) DNA in order to line up a sequence of DNA at a specific gene locus and then insert it into the DNA strand. A “gene drive” utilizes a recognized interaction between an organism’s homologous chromosomes in which one of the homologous chromosomes contains a specific DNA sequence that makes an enzyme that spontaneously cuts the DNA sequence of the other chromosome. This is very similar to CRISPR except that in this system the “cutting” gene sticks a copy of itself into the severed DNA sequence. The “gene drive,” then, results in the amplification of a gene passing through generations in a population.

These CRISPR/gene drive systems have been evaluated carefully since for many of these applications their theoretical outcome is the extinction of their target species. Nature, however, seems to have some other ideas in this matter.

For example, a paper in Science Advances (May 19, 2017) found that genetic variations at the CRISPR insertion site, even quite rare variations, can interfere with the success of the gene insertion. Researchers found that even a 1% gene variation at a CRISPR site was enough to negate any attempted CRISPR/gene drive control in as few as six generations. The use of these CRISPR systems, then, can only be successfully applied to a very select number of extremely non-variable genes.

Anopheles minimus. CDC, Public Domain

Also, a paper published in PLOS GENETICS (October 4, 2017) showed that mutations in a population of Anopheles mosquitoes into which a reproduction disrupting gene drive had been inserted quickly restored fertility in the mosquitoes and broke down the operation of the gene drive.

As Dr, Ian Malcolm (played by Jeff Goldblum) said so memorably in Jurassic Park, “life, uh, finds a way!”

Another, slightly less elegant way to control insect populations is to infect them with bacteria that disrupt their reproduction or life cycle. Male mosquitoes infected with the bacterium Wolbachia pipientis, for example, produce fertilized eggs that do not survive. Release of large numbers of Wolbachia infected male mosquitoes, then, should result in declines in the mosquito population.

Aedes albopictus Photo by J. Gathany CDC Wikimedia Commons

The Asian tiger mosquito (Aedes albopictus) is an exotic species that is steadily spreading across the eastern, midwestern and southwestern United States. Periodically, Asian tiger mosquitoes are even collected here in Western Pennsylvania in the summer, and there is evidence that the species may be evolving a tolerance to our long, cold winters. These tiger mosquitoes can carry a wide variety of pathogens including the viruses that cause yellow fever, Denge fever, Chickungunia and Zika. (see Signs of Spring 13, May 19, 2016 for more discussion of Asian tiger mosquitoes).

Control of Asian tiger mosquitoes is difficult because of the species’ great flexibility in reproduction (even very small water pools are sufficient for their egg laying and larval development) and the mosquito itself can tolerate very wide ranges of environmental conditions. The use of Wolbachia infected males to try to control tiger mosquitoes was approved by the EPA last year. This summer Wolbachia infected male Asian tiger mosquitoes will be released in twenty states under the direction of the biotech company MosquitoMate.

Controlling pest organisms via inducing changes in their genes or infecting them with bacteria, then, are two approaches for biocontrol. Another approach involves changing the plants on which the pest (typically a crop destroying pest) feeds. One of the most common ways that a crop can be modified for biocontrol is to insert a gene into the plant that codes for the synthesis of a chemical that acts as an internal pesticide. For the past twenty years a very common insecticidal insertion into plants has been the toxin producing gene from the bacterium Bacillus thuringiensis (Bt). These Bt-modified plants have included corn, cotton and soybeans. According to some 80% of all corn and cotton grown in the United States is now Bt-modified.

Photo by Pixabay

In a paper published in Nature Biotechnology (October 11, 2017) researchers at the University of Arizona document the growing resistance of a variety of potential crops pests to the insecticidal toxins produced in the Bt-modified plants. The precipitous decline in the effectiveness of Bt-modification was startling. It was noted, however, that the use of cropland “refuges”  (fields in which non-Bt-modified crops were planted adjacent to the fields with the Bt-modified plants) slowed down the development of Bt resistance. These refuges, apparently, increased the chances that a Bt-resistant pest individual would mate with a non-Bt-resistant pest individual, thus slowing down the spread the Bt-resistance gene in the pest population.

So there are lessons here: a year ago it seemed like CRISPR and gene drives would allow us to so precisely tinker with human pathogens and crop pests life cycles that we could easily eliminate both vector transmitted diseases and a long list of serious crop pests within a few generations of their life cycles. Many scientists began to envision a world free of disease and in which food crops could be grown with maximum efficiency. We now know that we didn’t really understand the system with which we were working. We now know that the forces of evolution will resist our clumsy attempts to take control of Nature.  We need to know so much more!



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Signs of Summer 11: The Biology of Smell

Photo by D. Sillman

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Almost every living organism can detect chemicals in its environment. From our large, complexly structured, vertebrate perspective, we call this chemosensory ability the “sense of smell” (or, more precisely, “olfaction”). The organ used to accomplished olfaction is, of course, the nose. Over the range of living things, though, “noses” come in many different forms!

The “nose” of a bacterium, for example, is a protein located on the surface of the cell. In E. coli, a gram negative (i.e. double plasma membraned) bacterium that is one of the most common organisms used in molecular biology research, there are specific protein receptors for environmental chemicals both on the inner plasma membrane and in the periplasmic space in between the inner and outer plasma membranes. When a chemical binds with one of these proteins a cascade of receptor and enzyme changes involving methylation and phosphorylation of intermediates occurs that alters the behavior of the bacterium. Further,  both inhibition or activation of a single receptor system causes adjacent receptor protein systems to similarly react leading to an amplification of the message and response (

Amoeba proteus. Photo by N. Hulsmann, Flickr

The ”nose” of the common protozoan, Amoeba, is also a protein on its plasma membrane. When environmental chemicals bind to these receptor proteins a cytoplasmic G-protein signaling system is activated. Phosphorylation and subsequent dissociation of the G-protein components in the Amoeba’s cytoplasm trigger signaling cascades that lead to physiological (and behavioral) changes in the organism (changes that might include movement toward and endocytosis of attractants or movement away from repellants). G-protein systems are also seen in most olfactory receptors throughout both invertebrate and vertebrate animal phyla! (Guetta, Dorian et al. “FYVE-Dependent Endosomal Targeting of an Arrestin-Related Protein in Amoeba.” Ed. Diane Bassham. PLoS ONE 5.12 (2010): e15249. PMC. Web. 15 July 2018).

The “nose” of a jellyfish is made up of specific chemosensory proteins that cover most of its body surface (both on its dome-shaped bell and also on its tentacles). These epidermal receptors are directly exposed to chemicals in the jellyfish’s environment and trigger G-protein changes in the receptor cells that may stimulate directed movement in the jellyfish or the release of protective nematocysts.

Planaria (Dugesia subtentoculata) . Photo by E. Sola, Wikimedia Commons

Planaria are a type of free-living flatworm. A major evolutionary advance in flatworms over jellyfish is the development of a head! A planarian’s head has two eyespots that are sensitive to light and two lateral projecting auricles (earlike structure) that have both tactile and chemical receptors embedded in them. A flatworm’s “nose”, then, is in its “ears.” (Shirsat N, Siddiqi O. 1993. Olfaction in Invertebrates. Curr Opin

Neurobiol. Aug;3(4):553-7.)

The nematode  Caenorhabditis elegans is another extremely common lab organism in molecular biology. Around its anteriorly located lips are sets of sensory structures that house its chemosensory cells (its “nose”). Both volatile and water soluble chemicals can be detected by these cells which then trigger positive responses to food and negative responses to potential dangers or threats. Most of C. elegans’ nervous system and more than five percent of its genes are associated with the recognition of environmental chemicals (there are 600 gene sequences in C. elegans associated with olfactory receptors!) . The G-protein systems in these olfactory receptors is also well documented. (

Grasshopper. Pixabay.

As invertebrates and then vertebrates develop more and more complex organ systems, the location of the cells that house the plasma membrane bound receptor proteins often becomes more and more specialized. Crayfish “smell” (and also feel) with their antennae as do butterflies and grasshoppers. In fact, these stalked, extended linear “noses” are very common throughout the phylum Arthropoda.

In vertebrates, the chemical receptor proteins (now called olfactory receptors or odorant receptors or “OR’s” for short)) are located on the olfactory sensory neurons in the epithelium in the nose. When an odorant chemical binds to an OR site a G-protein cascade is induced in the olfactory neuron leading to the generation of an action potential (and nerve impulse). Each OR has a range of specific chemicals to which it can react and each odorant chemical has a range of types OR’s to which it can bind.  This binding and response complexity makes the olfactory system responsive to an incredibly wide range of odorant chemicals, but causes some ambiguity in the generated sensory information. Novel scents can be readily detected but their precise sensory signaling signature and subsequent identification can be quite obscure.

Photo by A. Levine, Wikimedia Commons

In humans,  there are over 900 human OR genes spread out over more than 100 chromosomal locations. Twenty-one of the twenty-three human chromosomes contain OR genes (only chromosome 20 and the Y chromosome lack OR coding). Two-thirds of these human OR genes , though, are non-functional. So somewhere between 300 and 400 human genes are actually coding for OR receptor proteins. Humans have approximately six million OR sites in their olfactory epithelium.

In dogs,  our super-smelling best friends, 817 gene sequences for OR’s were identified in a recent study. These genes were found on twenty-four of the dog’s thirty-nine chromosomes in thirty-seven distinct regions. It is estimated that dog’s have about 30% more kinds of olfactory receptors than humans.

The comparison of human and dog OR genes suggests a strongly conserved distribution of genes. This implies that the OR genes of both species (and possibly many other mammals) evolved from a common mammalian ancestral source. These ancestral genes were so useful that they were passed along relatively unchanged through a long succession of evolutionary transformation.  The dog OR gene compliment, though, is more expansive and diverse than of humans and contains a rich array of unique, canine OR genes. This suggests that evolution of the dog’s olfactory system involved building on the highly conserved common genes by the addition of novel genetic adaptations.

Dogs in addition to having a greater diversity of OR receptors also has an olfactory epithelial area that is 20 times larger than that of humans. They also have thirty million olfactory receptors (six time more than humans) packed into the olfactory area of their noses. The anatomy of a dog’s nose also funnels a significant percentage of inspired air directly to the olfactory epithelium. Humans must consciously, and vigorously sniff to drive even a small percentage of their inspired air to their olfactory-sensitive cells. Further, the area of a dog’s brain devoted to olfaction is forty times larger than the olfactory area of a human brain.  The detection and processing of these environmental scents in a dog is an experience that is probably beyond the comprehension of a human!

One thing that humans can do much better than dogs is drive scent molecules from their pharynxes up into their nasal olfactory epithelium. This type of “smelling” (which is a critical part of tasting!) is called retronasal olfaction (the regular smelling straight in through the nose is called “orthonasal olfaction”). With our human retronasal olfaction we are able to taste the exquisite array of molecular components of our food. Without it, I bet everything would taste like dog food!

(Discussion of OR genes is primarily from Quignon, Pascale et al. “Comparison of the Canine and Human Olfactory Receptor Gene Repertoires.” Genome Biology 4.12 (2003): R80. Print.)

(Coming soon: an olfactory field trip through the woods!)

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Signs of Summer 10: To Anthropocene or not to Anthropocene?

Image by C. Khabbat, Wikispace

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One of the things about science that puts many people off is the incredible number of words that you need to learn to be able to talk about (or listen to) scientific ideas. Really bad science teachers, in fact, stress the word aspects of science so much that their students begin to believe that science is just a list of odd (but picky and precise) terms and facts that need to be memorized. I apologize to everyone who has had such an ill-informed and ignorant teacher!

We do need, though, some precision of language and some terms that express ideas beyond our everyday experiences in order to explore many scientific ideas. Words like the terms in the hierarchy of the Geologic Time Scale, for example, allow us see and discuss things that go far beyond days of the week or months of the year. I am sorry, though, for having to introduce so many funny names!

Image by Dragonsflight, Wikimedia Commons

I am writing this on Tuesday, July 24, 2018. This day, like all of my previous days and, I hope, all of my days to come are in the sub-division of Earth’s geologic existence called the Phanerozoic Eon. The Phanerozoic Eon started about 541 million years ago when living organisms “suddenly” became both more complex and more abundant! The Phanerozoic Eon, then, is defined as the span of time when the Earth has abundant plants and animals.

There were three eons before the Phanerozoic: the Hadean, the Archean, and the Proterozoic Eons. Collectively these three eons are lumped into a phase called the Precambrian supereon which spans the first four billion years of the life of the Earth (or, to orient these numbers clearly, the first 90%, or so, of Earth’s existence).

The past 541 million years, this Eon of Life, then, is just a blink of the geologic eye in the span of “Earth time!”

The Phanerozoic Eon, like all eons, is divided up into eras. There are three eras named to express the stage development of life on Earth: Paleozoic (“early life”), Mesozoic (“middle life”) and Cenozoic (“new life”). Tuesday, July 24, 2018, of course, is in the Cenozoic Era (which has been going on for the past 66 million years (ever since something really bad happened to 75% of the species that had dominated the Mesozoic!).

Asteroid impact ending the Mesozoic Era, D.E.Davis, Public Domain

The Cenozoic Era is divided up into three periods: the Paleogene, the Neogene, and the Quaternary. The Quaternary Period is the most recent of these periods and represents the past 2.6 million years. This is the time in which humans (defined as individuals of the genus Homo) have existed. This is also the time of the Ice Ages and the present day “warm” period (which, in fact, may be just a pause in the ice age cycle (we’re not absolutely sure about that)). These two events (Ice Ages and non-Ice Ages) serve as the basis for the two epochs of the Quaternary Period (epochs are, of course, divisions of periods): the Pleistocene (2.5 million years of ice advances and retreats across the face of the globe) and the Holocene (the past 12,000 years, or so, when the Earth has been warm and relatively ice-free (and during which humans developed agriculture and all of our other technologies!).

Alaskan glaciers. Photo by Roger W. Flickr

Epochs, by the way, are divided up into Ages. The 12,000 years of the Quaternary Epoch is divided pretty evenly (about 4000 years each) into three Ages: the Greelandian Age, the Northgrippian Age, and the Meghalayan Age. The onset of the Meghalayan Age began with the global climate shift that led to the end of the great, ancient human civilizations of North Africa, the Mediterranean, the Middle East, India and China.  We, here on July 24, 2018 are in year #4,200 (possibly at the very end!) of the Meghalayan Age.

So what comes next? Is there a new Age in the wings waiting to come into definition?

There was a proposal a few years ago to call the “now” the Homogenocene to emphasize the influence of humans in the homogenization of the distribution of plants all around the world (see Signs of Spring 11, 2017). There have also been proposals to define the “now” in broader terms that emphasize more of the scope and magnitude of the human influence on the land, sea and air systems of the Earth. These proposals are all wrapped up in a geologic term called the Anthropocene.

The Carnegie Museum of Natural History in Pittsburgh has (until Sept. 3, 2018) an exhibition in which the characteristics of the proposed Anthropocene are displayed. Deborah and I had the chance to see this exhibition in May with our friends Patrick and Mardelle Kopnicky.

Photo from Grendz,com

The exhibit illustrated human impacts on coral reefs, on plant flowering and leafing times, on domesticated and wild animals, on extinction rates, on habitats, on climate, and on the composition of the atmosphere itself. The astounding amounts of plastics produced, used, and then discarded into landfills, fresh water systems and the oceans were graphically and visually displayed. The wall-sized photograph of a surfer wrapped up in the curl of a wave that was densely packed with floating plastic debris is an image I cannot get out of my mind. These plastics represent the introduction into the systems of the Earth materials that have never existed before in Nature (see Signs of Fall #4, 2017). Their ultimate impacts on the Earth are still unclear.

The astounding (and growing) number of human beings on Earth (another feature of the Anthropocene) leaves one with the impression that none of the changes can ever be reversed (see Signs of Spring 3, 2016).

So what is the Anthropocene? Its name sounds like an Epoch. Something proposed to replace the Holocene? A committee of the International Commission on Stratigraphy (ICS) has proposed to make the Anthropocene the next geologic Age (i.e. the next subdivision of the Holocene). This proposal must then be voted on by the entire ICS and then approved by the International Union of Geological Science. The Anthropocene would not be a new Epoch (the Holocene still is incredibly new and appropriately defined), but it would be a logical continuation of the Ages of the Holocene emphasizing the prime force that is shaping our planet today: us.



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