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Cope's gray treefrog (H. chrysoscelis) and the Eastern gray treefrog (H. versicolor) are a unique example of speciation in action. The two species have very similar genes, and appear identical; however, the eastern gray treefrog possesses a second chromosome set, twice the number of chromosomes as Cope's gray treefrog. Cope's (H. chrysoscelis) is called a diploid, and the eastern (H. versicolor) is called a tetraploid. The only reliable ways to distinguish between the species are by the calls of the males or by microscopic examination of their chromosomes.
H. versicolor is thought to have evolved from H. chrysoscelis when an extra chromosomal set was passed to several surviving egg masses sometime early in the Pleistocene epoch, commonly known as the "Ice Age." At this time, populations of H. chrysoscelis were isolated by intervening areas of extreme low tempoeratures. By the time the climate warmed and the glaciers retreated, the two populations had evolved in different directions, and though they now occur together, they no longer interbreed and are different species.
The western fox snake (Pantherophis vulpinus) and eastern fox snake (Pantherophis gloydi) of the Great Lakes Basin in North America are another example of this pattern of speciation. The habitats and prey vary greatly between these two species, yet except for minimal variation of their scale patterns they almost appear identical.
The male's advertisement call is the main trait to distinguish the eastern gray treefrog (H. versicolor) from Cope's gray treefrog (H. chrysoscelis). In general, the sound is comprised of a resonant musical trill. The eastern gray treefrog has a slower trill than Cope’s, which is faster and higher pitched. An increase in air temperature raises the rate of the trill and tape recordings may be necessary for positive identification, especially if only a single species is present.
In comparison to other frog species in the range, the gray treefrogs calls are shorter, only 0.5 to 3 seconds, yet similar to the call of the American toad (Anaxyrus americanus). The spring peeper (Pseudacris crucifer) also uses a similar call, but several ‘peeps’ can be heard before and after the trill.
In the larval state, Hyla versicolor uses chemoreception as its primary method of communication and defense against predators. Predatory fish and salamander larvae are detected via chemoreception. Injured tadpoles also release an "alarm substance" to warn their conspecifics.
Adult gray treefrogs are very sensitive to ground vibrations and possess excellent hearing. Yet, during hibernation they are unresponsive to most external stimuli.
Communication Channels: visual ; acoustic ; chemical
Other Communication Modes: choruses
Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical
Hyla versicolor is not currently classified as endangered or of special concern. However, habitat destruction and human pollutants are contributing to the overall decline of amphibians, including frog and toad species. Public support of habitat areas in state parks, nature reserves, and private property continues to promote the survival of amphibian species. Ongoing scientific research also improves our understanding of this dynamic species.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Tadpoles of the eastern gray treefrogs metamorphosize into froglets in six to eight weeks. The young frogs are approximately 0.6 in. (1.5 cm) snout to vent length. The larval and adult rate of growth is dependent on the availability of food and stress of predators. The sex deterimination of amphibians is genetic. However, if larvae are treated with estrogen, then hormonal sex reveral is possible after metamorphosis. Hyla versicolor follow the XX/XY pattern of heterogamety.
Development - Life Cycle: metamorphosis
There are no known adverse effects of Hyla versicolor on humans.
People benefit from the substantial amount of insect pests that are eaten by H. versicolor. The spring breeding chorus also provides evening entertainment to re-affirm our connection with nature. We also use the presence of eastern gray treefrogs as a scientific tool to indicate the overall biodiversity and the level of contaminants in a region. Overall, the eastern gray treefrog plays an important role in the ecological balance of wooded farmlands and residential areas and contributes to our own well-being.
Positive Impacts: controls pest population
Eastern gray treefrogs can play a critical role in the foodweb of their ecosystems. As tadpoles they may graze enough algae to change the community of algal species in their ponds. Later, local pest populations of mosquito, gnats, and flies are reduced in the territory of a single gray treefrog. In turn, Cope's gray treefrogs are the prey of larger frogs, carnivorous birds, and small mammals. H. versicolor are a significant link to support the survival of other animals in the ecosystem.
Like just about all animals, this species is host to parasitic species. Among others, Polytoma nearcticum is a flatworm that lives in the gills of tadpoles and the bladder of adults. Nematodes in the genus Strongyloides are found in the digestive systems of these frogs.
Commensal/Parasitic Species:
As tadpoles, eastern gray treefrogs begin life by grazing on algae and detritus in their pond.
After metamorphosis, H. versicolor prey upon most types of insects and their larvae. Mites, spiders, plant lice, harvestmen, and snails are also eaten. Gray treefrogs mostly hunt insects in the understory of wooded areas in small trees and shrubs, where they may rely upon their camouflage with less risk of predation. However, like most frogs, H. versicolor is opportunitistic and may also eat smaller frogs, including other tree frogs.
Animal Foods: amphibians; insects; terrestrial non-insect arthropods; mollusks; terrestrial worms
Plant Foods: algae
Other Foods: detritus
Primary Diet: carnivore (Insectivore ); herbivore (Algivore)
Both gray treefrog species, Hyla versicolor and Hyla chrysoscelis, inhabit a wide range from southern Ontario and Maine, westward to central Texas, northwest to Manitoba, and northern Florida. An isolated colony is also noted in New Brunswick. The two species appear physically identical, and consequently more studies are necessary to delineate where the species overlap.
Generally, the eastern gray treefrog (H. versicolor) is mostly found to the north and northeast of the range. However, the gray treefrog species are extremely variable in their distribution pattern. For instance, the eastern gray treefrog is common in the eastern Great Lakes region, including southern Michigan; however, both species: H. versicolor and H. chrysoscelis share the same breeding ponds in Wisconsin and northern Michigan.
Biogeographic Regions: nearctic (Native )
Eastern gray Treefrogs inhabit all elevations of wooded areas near temporary and permanent waters in such diverse surroundings such as swamps, ponds, lakes, old fields, thickly wooded suburban neighborhoods, farm woodlots, and mixed or deciduous forests. During the summer months, they are most often found in damp rotten logs or hollow trees. In winter, gray treefrogs hibernate on land under woody debris such as logs, roots and leaf litter.
Habitat Regions: temperate ; terrestrial ; freshwater
Terrestrial Biomes: forest
Aquatic Biomes: lakes and ponds; temporary pools
Wetlands: swamp
Other Habitat Features: suburban ; agricultural ; riparian
One captive gray treefrog lived for over seven years in captivity. Unfotunately, it was not distinguished as H. chrysoscelis or H. versicolor. The potential lifespan in captivity and the wild is unknown. It is likely that few gray treefrogs die of old age, predators, disease and climactic extremes are more likely causes of death.
Range lifespan
Status: captivity: 7 (high) years.
Average lifespan
Status: captivity: 7 years.
The eastern gray treefrog measures 1.25 to 2 inches (3-5cm) in length. The record length is 2.25 in. (6 cm). There is no sexual dimorphism. The dorsal surface of the gray treefrog species is rough and lightly sprinkled with warts,more than most frogs but less than the average toad. The large toepads produce mucous to adhere to smooth bark or man-made structures near light sources, and are characteristic of the family Hylidae. The colors of a gray treefrog vary with the colors of its background and environmental factors such as season and humidity, but shades of gray are most common with black blotches on the back. Variations of brown, green, and pearl-gray colors have been noted. Green colors are more prominent during the breeding season and in yearling frogs. Usually, there is a white mark beneath the eye. The ventral skin on the hind legs, in the groin region, may appear orange to golden yellow with black speckles and the belly is white.
If the coloration is in question, place the treefrog in a box, allow it to sit quietly, and later re-examine the specimen. The yearling frogs are about half the size of the older H. versicolor population, but retain the same characteristics. Gray treefrogs continue to grow each year until they achieve the physical limit of the species.
Both gray treefrog species possess the same larval traits, but H. versicolor was used to exemplify the tadpole stage in Conant and Collins' "A Field Guide to Reptiles and Amphibians of East Central North America". The tadpoles are small, but colorful, 1.25 in. to 1.5 in. (3.2 cm. to 3.8 cm.) long. The tip of the tail is well-defined with a 5 mm narrow tip. The oral disc is comprised of 2 upper labial tooth rows and 3 lower, serrated jaws, and an overhanging upper jaw. The intestinal coil is also visible. The background color is light green to yellow. The tallest section of the tail fin is the middle and heavy black dots are scattered along the margin on a red or orange background across the tail.
Range length: 3 to 5 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike
Average mass: 7.175 g.
Average basal metabolic rate: 0.00433 W.
Many assorted species of birds, snakes, other frogs, and small mammals eat gray treefrogs. These frogs are arboreal to avoid predators, and exploit new food resources. They also avoid the attention of predators by calling after dusk and being most active in the evening and night. They use cryptic coloration and rarely leave the trees until the breeding season. Their skin is able to assume most natural colors in which it comes into contact.
Larger frogs, such as the bullfrog (Lithobates catesbeianus) and green frog (Lithobates clamitans clamitans, have been observed to consume gray treefrogs by stalking calling males. In the water, giant waterbugs (Belostomatidae) also attack Cope's gray treefrog.
In the larval state, gray treefrogs are subject to predation by fish and larger amphibian larvae, such as the tiger salamander (Ambystomma tigrinum). When aquatic predators are abundant, gray treefrog tadpoles reduce their activity and feeding. They grow more slowly, and metamorphose at a smaller size.
Known Predators:
Anti-predator Adaptations: cryptic
The breeding choruses of gray treefrogs begin in late April to early May after the evening air temperature rises above 15°C, which varies throughout the range. These frogs end their hibernation in the early months of spring, but do not have the energy reserves to call, yet. Warm, cloudy nights, from dusk to midnight, produce the most intense choruses. However, interludes of cold weather may temporarily end the male gray treefrog calls. Generally, the breeding chorus lasts for several weeks. Sometimes, the breeding calls are continued into late June or early July, depending on local temperatures and unusual weather phenomena.
Female choice dominates the mating scheme of gray treefrogs, since the female approaches the male with the most prolonged and frequent calls. If the male detects a nearby female he will also further entice her with a “courtship call” that is longer and more emphatic than the usual advertisement call. Successful calling results in amplexus as the female deposits eggs which are externally fertilized by the male. Almost immediately, the large egg mass breaks into small, loose egg clusters of 10 to 40 eggs attach to plants or other structures within the pond. Depending on the water temperature, the tadpoles hatch in three to seven days. Both gray treefrog sp. do not hybridize due to a mating barrier, the different pulse rate and pitch between the two calls.
Mating System: polygynous
Eastern gray treefrogs employ their unique call from the safety of vegetation next to the shallow breeding sites, preferably in tree branches that overhang the water. The males aggressively defend and use their voice to outline their territories with extended calls. Satellite males, often in their first breeding season or otherwise disadvantaged, do not call to save energy. Instead, they lie in wait near a calling male and intercept the female by claiming the caller’s position after he moves away. The female only visits the breeding site to lay her eggs. During the last weeks of the breeding season, occasional calls may still be heard as the males slowly retreat from the shoreline and disappear into the foliage. Rare calls may still be heard in the trees in late summer or fall, yet they are unrelated to mating, and occur more often during rain showers. Calling males are often attacked by predators, and this results in a female-biased population.
Breeding interval: Treefrogs breed once yearly.
Breeding season: Late April to May or until the temperature rises above 15°C
Range number of offspring: 1,000 to 2,000.
Range time to hatching: 3 to 7 days.
Average age at sexual or reproductive maturity (female): 2 years.
Range age at sexual or reproductive maturity (male): 1 to 2 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
Average age at sexual or reproductive maturity (female)
Sex: female: 912 days.
Female gray treefrogs invest in their offspring by providing yolk to the eggs, and choosing ponds that are relatively free of predators (they especially try to avoid fish). Males do not invest in the offspring, and female investment ends when she lays her eggs.
Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth
