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

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of treefrog found in the United States and Canada. 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 choi ...

— 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 (scansorial), but others are exclusively arboreal. The hab ...

, 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 Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...

described the species in 1880. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

, ''chrysoscelis'', is from Greek ''chrysos'', gold, and ''scelis'', leg. Microscopic inspection of the

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

s of ''D. chrysoscelis'' and ''D. versicolor'' reveals differences in chromosome number. ''D. chrysoscelis'' is

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

, 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 two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...

, 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 g ...

, 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 varieties, subspecies, species or genera through sexual reproduction. Generally, it means that each cell has genetic material from two di ...

sympatry In biology, two closely related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter each other. An initially interbreeding population that splits into two or more distinct spe ...

. To enforce speciation there may be unknown mechanisms of

reinforcement In Behaviorism, behavioral psychology, reinforcement refers to consequences that increase the likelihood of an organism's future behavior, typically in the presence of a particular ''Antecedent (behavioral psychology), antecedent stimulus''. Fo ...

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. The pattern and color variations of skin for this species will change depending on the environment they are found in. Similar hidden bright patterns are common in various

Lepidoptera Lepidoptera ( ) or lepidopterans is an order (biology), order of winged insects which includes butterflies and moths. About 180,000 species of the Lepidoptera have been described, representing 10% of the total described species of living organ ...

, for instance moths of the genus ''

Catocala ''Catocala'' is a generally Holarctic genus of moths in the family Erebidae. The genus was erected by Franz von Paula Schrank in 1802. The moths are commonly known as underwing moths or simply underwings. These terms are sometimes used for a fe ...

''.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 sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

. 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. . Usually, the younger frogs in this species will often be seen more with the greenish color throughout the breeding seasons. As they age they will lose the greenish color and move towards the distinct gray color. 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 ...

Distribution and habitat

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

Piedmont Piedmont ( ; ; ) is one of the 20 regions of Italy, located in the northwest Italy, Northwest of the country. It borders the Liguria region to the south, the Lombardy and Emilia-Romagna regions to the east, and the Aosta Valley region to the ...

and

Coastal Plain A coastal plain (also coastal plains, coastal lowland, coastal lowlands) is an area of flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and an upland area. Formation Coastal plains can f ...

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 Manitoba. ''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. When studying ice concentration of overwintering frogs, 40-50% of total body water was frozen. Studies have revealed that Cope's gray treefrog could be more resilient to climate change in the long-term, though populations may suffer short-term drawbacks. Either way, distribution will hopefully change little in the long-term because of this. 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 decibels. Females prefer calls with average frequencies over calls with frequencies that were 2 or 3 semitones lower than the population mean. Calls higher than the average semitones do not face behavioral discrimination like the lower calls do. 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. Cope's gray treefrog exhibits freeze tolerance. ''Dryophytes chrysoscelis'' is capable of surviving temperatures as low as . They can withstand the physiological challenges of corporeal freezing, by accumulating cryoprotective compounds of hepatic origin, including glycerol, urea, and glucose. It is one of a few freeze tolerant frogs that use glycerol as a cryoprotectant.

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