Amphibians

 

Green Treefrog (Hyla cinerea).
Mecklenburg County, North Carolina. 

Amphibians, our frogs, toads and salamanders usually have moist skin and are dependent on water for at least part of their life cycle.  All amphibians start out as a fertilized egg.  The egg develops into a tadpole, an aquatic creature with gills much like a fish.  The tadpole then transforms into a four-legged, air-breathing land animal with lungs.  The name amphibian reflects this type of life.  It is from the ancient Greek meaning two forms of life, life in the water and life on the land. 

 

Video of frog tadpoles.

Rowan County, North Carolina. 

Amphibians are, in part, the inspiration of an impressive and enigmatic phrase I first heard while taking freshman biology, “Ontogeny recapitulates phylogeny”.  I was assigned to write an essay on this theory and that assignment sent me to the library.  Some might remember libraries; they were the internet of their day.  Scouring indices of several books yielded a definition; Ontogeny (development) recapitulates (gives a summary of) phylogeny (evolutionary history).  In the case of amphibians, the theory says they pass through the single-cell organism stage, then become a fish-like animal, then a land animal.  This sequence supposedly recapitulates vertebrate evolution because all vertebrates have a similar developmental sequence.  Further reading informed me ontogeny recapitulates phylogeny is no longer accepted by science.  The similarity of development among vertebrates is a reflection of their common ancestry not some form of genetic memory. 

North Carolina is the home to 71 species of amphibians.  Much of this diversity is from the dizzying array of salamanders found in the North Carolina mountains.  

The Red Eft stage of the Eastern Newt (Notophthalmus viridescens).
Ashe County, North Carolina. 

The Red Eft is the juvenile stage of the Eastern Newt (Notophthalmus viridescens), a species of salamander.  The Eastern Newt is found throughout North Carolina.  Tadpoles of this salamander metamorphose into the Red Eft. This is a highly terrestrial stage of the Eastern Newt life cycle.  Red Efts may walk long distances to reach distant bodies of water.  This wide-spread dispersal prevents inbreeding in the species.  After spending several years as a Red Eft, the Eastern Newt undergoes a second metamorphosis into the aquatic adult, the reproductive stage.  Red Efts have rough, dry skin, an unusual feature in salamanders.  This is an adaptation to the dry environment most salamanders avoid.  The Red Eft’s color is a warning.  The brilliant red lets predators know the Red Eft’s skin is permeated with tetradotoxin, a powerful neurotoxin and so should not be eaten.

Marbled Salamanders (Ambystoma opacum).
Rowan County, North Carolina. 

The Marbled Salamander (Ambystoma opacum) is another widespread amphibian species.  This rather large salamander is black with white bands on its back.  They hide under leaves and logs, and they eat worms, slugs and insects.  During the fall, Marbled Salamanders mate and the females lay eggs in forest depressions. As the depressions fill with rainwater, tadpoles develop and metamorphose into the adult stage. 

Cricket Frog (Acris crepitans).
Mecklenburg County, North Carolina. 

Frogs and toads are another major group of amphibians and are well represented in North Carolina. Northern Cricket Frogs (Acris crepitans) are usually found on the Piedmont of North Carolina.  This tiny frog is brown and green, has warty skin, a dark triangle on the head and a Y-shaped pattern on the back.  The call of Northern Cricket Frogs is a series of rapid clicks resembling the sound of its insect namesake. 

A Green Treefrog blending into foliage.
Rowan County, North Carolina. 

Several treefrogs are found in North Carolina.  Treefrogs are rarely found on the ground and have large toepads that allow them to climb vertical surfaces.   Among the most common are the Green Treefrog (Hyla cinerea) and two species of Gray Treefrogs (Hyla chrysoscelis and Hyla versicolor).  Green Tree Frogs live on the Coastal Plain and Piedmont of North Carolina where they blend in perfectly with vegetation.  Their green color is set off by a white stripe on each side and golden spots on the back.  

Cope's Gray Treefrog (Hyla chrysoscelis).
This frog used the adhesive pads on its toes
to climb up a glass window pane. 
Rowan County, North Carolina. 

Cope's Gray Treefrog seen from below.
Rowan County, North Carolina. 

A Cope's Gray Treefrog looking out from a Bluebird box.
Rowan County, North Carolina. 

The two species of Gray Treefrogs found in North Carolina belong to a cryptic species complex and are visually indistinguishable.  H. chrysoscelis is called Cope’s Gray Treefrog and H. versicolor is the Gray Treefrog.  Both Gray Treefrogs are mottled gray, brown and green and can change their color, chameleon style.  The underside of these frogs is white with bright yellow on the hind legs.  The two species can be distinguished by their calls, with H. chrysocelis having a faster call than H. versicolor.  A definitive if not very practical way to distinguish the two Gray Treefrogs is by counting their chromosomes.  H. chrysoscelis is diploid, with two copies of each chromosome, while H. versicolor is tetraploid with four copies of each chromosome.   The speciation event that produced the two species of Gray Treefrogs occurred by of multiple hybridizations between H. chrysoscelis and several related treefrog species that are now extinct.  

Fowler's Toad (Anaxyrus fowleri).
Dare County, North Carolina. 

Toads are related to frogs but with dryer, warty skin.  The legs of toads are shorter than those of frogs and this makes them more likely to crawl than hop.  Fowler’s Toad (Anaxyrus fowleri) is found throughout North Carolina, from the mountains to the coast. This medium-sized toad has a gray body with dark brown spots. 

 Amphibians are intrinsically interesting creatures but they are also sensitive indicators of environmental quality.  The moist skin of amphibians absorbs not only water and oxygen, but also toxins and pollutants. This makes amphibians sensitive to environment degradation and many species are in decline.  Perhaps worse than pollution is amphibian susceptibility to novel infectious diseases. Two species of infectious fungi called chitrids have emerged in the last 30 years and have devastated many species of amphibians around the world.  Frogs, toads and salamanders are treasures.  Their forms, colors and calls are a delight, and they tell us a story we need to hear.