Amphibians are the oldest group of terrestrial vertebrates. They arose during the Devonian Period of the Paleozoic Era some 370 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 developed as aquatic organisms (tadpoles of frogs are an excellent example of this). A few amphibian species, though, bypass both the need to lay eggs in water and the aquatic larval stages. In these predominantly tropical rain forest species, small, full-formed “adult versions” of the amphibian hatch from the eggs and immediately enter the terrestrial ecosystem.
Amphibians have been declining all around the world. Hays (Journal of Experimental Biology 213.6 (2010): 921-933) estimates that 70% of all amphibian species are decreasing in numbers and that 32% of all amphibians are facing immanent extinction. Reasons for the observed vulnerability of amphibians are complex: they are exposed to high levels of UV radiation in sunlight especially in their egg and larval pools, surface water sources have declined precipitously in quality especially due to the influx of agricultural chemicals from surrounding fields and the impacts of wastes from large numbers of domestic grazing animals. Also, the increased density and species diversity in the biotic communities of the water pools themselves (due to a reduction in the total number of suitable pools for habitation) has led to a rapid dissemination of diseases both intra-specifically and inter-specifically. The epidemic spread of the chytrid fungus is an example of this accelerated transmission of disease.
Amphibian skin is also extremely permeable. It allows oxygen and water and many other chemicals in the environment to freely pass into the body of an amphibian. Many amphibians, in fact, rely on this skin permeability to gather oxygen from their aquatic environments, but the uncontrolled accumulation of environmental pollutants can, of course, have very deleterious consequences.
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).
Much of the published data on amphibians is quite distressing. Population declines, lack of reproduction, and actual extinctions of populations are the most common topics in scientific papers about amphibians. There are a few hopeful observations, though.
For example, a paper published in Current Biology (May 21, 2018) explored the genetics of the six-foot long Chinese giant salamander and found that this largest, living amphibian in the world represents five (or maybe even more!) distinct species. These large salamanders inhabit freshwater habitats in China and tend to move only slightly from their place of birth. The consequence of this is that each distinct species is highly adapted to the specific conditions of their ancestral habitats. Recent conservation programs in China, though, which have not been very successful, have assumed that these giant salamanders represented only a single species! So, captive breeding programs and subsequent re-introduction of the young salamanders that they produce have generated many cross-species hybrids and have not paid attention to matching the specific species to their specific types of habitats. Hopefully, the knowledge of the existence of the multiple species will allow a more precise breeding system to be established and lead to a re-introduction program that more closely matches each species with their optimal habitat conditions thus giving these extremely endangered species a better chance at recovery.
In Panama in the first decade of the Twenty-first Century, the invasive chytrid fungus decimated native frog populations. Researchers recently returning to Panama studied both the chytrid fungus (and its pathogenicity) and the immune systems of the native frog species (in particular the protein systems secreted by glands in the frog’s skin which have protective, anti-fungal properties). They found that the chytrid fungus(which was thought to have been introduced to Panama by human transport) was unchanged in its ability to infect amphibians. This surprised researchers who thought that the virulence of the fungus would have declined as it established an equilibrium with the native frogs. Many native frog species, though, have developed skin secretory proteins that are increasingly effective at killing the chytrid fungus. This change in skin proteins suggests an on-going, relatively rapid evolutionary change in the frogs in response to this extremely destructive pathogen. This study was published in Science (359: 1517-19, March 29, 2018).
And, finally, very close to home: a fisherman fishing in the nearby Kiskiminetas River this spring hooked (and then videotaped and released) a hellbender salamander. The hellbender is the third largest salamander in the world (total length is up to 29 inches) and its eastern North American distribution has been rapidly shrinking due to habitat degradation. Hellbenders require clean water with high levels of oxygen (usually generated by fast turbulent waterflow over large, irregular rocks). They primarily eat crayfish but will also take small fish (especially in the winter).
The discovery of a hellbender in the Kiski River is an incredibly powerful affirmation on the on-going ecological recovery of this once polluted and acidified stream. Insects returned to the Kiski over recent decades followed by an array of fish species. And now, we have hellbenders! Can mussels and otters be far behind? (see Mary Ann Thomas’ article in on-line Valley News Dispatch (May 3, 2018).
Amphibian populations reflect the quality of surface water resources. As surface waters are polluted and degraded, the amphibians decline, and as surface waters are rehabilitated and protected, amphibians rebound. We need to recognize that water is our most precious and our most important resource. Our own survival depends on on water! We need to protect all surface water systems. Keep your eyes on the amphibians to see how we are doing!