Cope's gray treefrog (''Dryophytes chrysoscelis'') is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

treefrog A tree frog (or treefrog) is any species of frog that spends a major portion of its lifespan in trees, known as an arboreal state. Several lineages of frogs among the Neobatrachia have given rise to treefrogs, although they are not closely relat ...

found in the United States. It is almost indistinguishable from the gray treefrog ('' Dryophytes versicolor''), and shares much of its geographic range. Both species are variable in color, mottled gray to gray-green, resembling the bark of trees. These are treefrogs of woodland habitats, though they will sometimes travel into more open areas to reach a breeding pond. The only readily noticeable difference between the two species is the

mating call A mating call is the auditory signal used by animals to attract mates. It can occur in males or females, but literature is abundantly favored toward researching mating calls in females. In addition, mating calls are often the subject of mate choic ...

— Cope's has a faster-paced and slightly higher-pitched call than ''D. versicolor''. In addition, ''D. chrysoscelis'' is reported to be slightly smaller, more

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose nu ...

, and more tolerant of dry conditions than ''D. versicolor''.Martof, B. S., et al. (1980). ''Amphibians and Reptiles of the Carolinas and Virginia''. Chapel Hill: University of North Carolina Press. .

Taxonomy

Edward Drinker Cope described the species in 1880. The specific name, ''chrysoscelis'', is from Greek ''chrysos'', gold, and ''scelis'', leg. Microscopic inspection of the

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

s of ''D. chrysoscelis'' and ''D. versicolor'' reveals differences in chromosome number. ''D. chrysoscelis'' is diploid, having two complete sets of chromosomes, the usual condition in vertebrates. ''D. versicolor'' is

tetraploid Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains ...

, having double the usual number of chromosomes. Generally, ''D. versicolor'' is believed to have evolved from ''D. chrysoscelis'' in the last major

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gre ...

, when areas of extremely low temperatures divided populations. Despite currently sharing habitat, the two species generally do not interbreed. ''D. chrysoscelis'' is known to be largely intersterile with ''D. versicolor'' but there may be a limited amount of

interfertility In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in ...

in sympatry. To enforce speciation there may be unknown mechanisms of

reinforcement In behavioral psychology, reinforcement is a consequence applied that will strengthen an organism's future behavior whenever that behavior is preceded by a specific antecedent stimulus. This strengthening effect may be measured as a higher fr ...

deployed between these species and further research may be fruitful.

Description

Both ''D. chrysoscelis'' and '' D. versicolor'' have black-marked bright orange to yellow patches on their hind legs, which distinguishes them from other treefrogs, such as ''D. avivoca''. The bright-yellow pattern is normally hidden, but exposed when the frog leaps. This "flash pattern" likely serves to startle a predator as the frog makes its escape.Tesler, P
Exploratorium The Amazing, Adaptable Frog.
The Exploratorium. San Francisco. Similar hidden bright patterns are common in various Lepidoptera, for instance moths of the genus '' Catocala''.Sargent. (1969)
A suggestion regarding hindwing diversity among moths of the genus ''Catocala'' OF (Noctuidae).
''Journal of the Lepidopterists' Society'' 23: 261-264. Both species of gray treefrogs are slightly

sexually dimorphic Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

. Males have black or gray throats in the breeding season, while the throats of the females are lighter.Tyning, T. F. (1990). ''A Guide to Amphibians and Reptiles.'' Boston: Little, Brown and Company. . H chrysoscelis male

Skin secretions from this species may be irritating or toxic to mouth, eyes, other

mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It i ...

Distribution and habitat

The range of ''D. chrysoscelis'' is more southerly; it is apparently the species found in the lower elevation

Piedmont it, Piemontese , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = , demographics1_footnotes = , demographics1_title1 = , demographics1_info1 = , demographics1_title2 ...

and

Coastal Plain A coastal plain is flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and a piedmont area. Some of the largest coastal plains are in Alaska and the southeastern United States. The Gulf Co ...

of Virginia and the Carolinas. In those areas, ''D. versicolor'' may be present only in the Appalachians. While this species is most abundant in the southeast, it can be found as far north as Minnesota. ''D. chrysoscelis'' has also been observed to practice freeze tolerance in a lab setting, which could help it survive in cold climates. These frogs are one of the very few that can mobilize glycerol as a cryoprotectant. Glycerol production is low when the temperature is warmer, but when it gets colder, the glycerol in the body is rapidly produced. They prefer to perch on pipes located along the edges of wetlands and close to trees, which suggests that the terrestrial habitat surrounding wetlands is an important component of the species habitat. The bird-voiced treefrog, ''D. avivoca'', is similar to ''D. chrysoscelis'' and ''D. versicolor'', but is smaller (25–50 mm in length vs 32–62 mm for the gray treefrog).

Behavior

In the Southeastern United States, Cope's gray treefrog breeds and calls from May to August. Isolated males start calling from woodland areas during warm weather a week or more before migrating to temporary ponds to breed. There they form aggregations (choruses) and call together. Chorusing is most frequent at night, but individuals often call during daytime in response to thunder or other loud noises. These individual calls are produced at high sound pressure levels (SPLs) reaching 85 to 90 dB and sustained noise levels in choruses commonly range between 70 and 80 dB SPL. Female treefrogs have been found to be able to differentiate calls at scales of up to a few decibals. Eggs are laid in batches of 10 to 40 on the surfaces of shallow ponds and other small bodies of water. These temporary bodies of water usually lack fish, and females preferentially lay their eggs in water bodies that lack fish or other predatory vertebrates and have lower desiccation risk. Eggs hatch in about five days and metamorphosis takes place at about 45–65 days.Rubio, M
Atlanta's Backyard Herps.
Accessed 2 June 2013. The diet of Cope's gray treefrog primarily consists of insects such as moths, mites, spiders, plant lice, and harvestmen. Snails have also been observed as a food source. Like most frogs, ''Dryophytes chrysocelis'' is an opportunistic feeder and may also eat smaller frogs, including other treefrogs. Once the breeding season is over, Cope's gray treefrogs will forage continuously until winter. ''Dryophytes chrysoscelis'' is capable of surviving temperatures as low as –8 °C.

References

do Amaral, M. C. F., Frisbie, J., Goldstein, D. L., & Krane, C. M. (2018). The cryoprotectant system of Cope’s gray treefrog, Dryophytes chrysoscelis: responses to cold acclimation, freezing, and thawing. Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology, 188(4), 611–621. https://doi.org/10.1007/s00360-018-1153-6

External links