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American green tree frog

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American green tree frog
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Order: Anura
Family: Hylidae
Genus: Dryophytes
Species:
D. cinereus
Binomial name
Dryophytes cinereus
(Schneider, 1799)
Approximate range
Synonyms[citation needed]
  • Calamita cinereus Schneider, 1799
  • Hyla viridis Holbrook, 1842
  • Hyla carolinensis Cope, 1889
  • Hyla cinerea Garman, 1890

The American green tree frog (Dryophytes cinereus or Hyla cinerea) is a common arboreal species of New World tree frog belonging to the family Hylidae. The species is nocturnal, of moderate size, and is colored bright green to reddish-brown. On average the frog weighs around 3.76g[citation needed], and females are larger than males in size.

The species is mainly found in the central and southeastern regions of the United States. It lives in open canopy forests or permanent waters with abundant vegetation. The species has suffered from habitat loss primarily due to urbanization and wildfires. When defending its territory, the frog will either emit aggressive call signals or grapple with intruders.

The female species breeds with males through amplexus at least once a year with its mating season lasting from March and April to August and September. The species has the potential to breed multiple clutches in a single mating season. Parental investment only includes mating and egg laying. Breeding is known to be influenced by day length, temperature, and precipitation. Male frogs will emit unique advertisement calls to attract potential female mates. Low frequency call signals are most attractive to females.[citation needed] During mating competition, the species will eavesdrop on neighboring competitors and either adjust its signal timing or remain silent as a satellite to intercept rival call signals and mate with approaching females. Male vocalization during mating is supplied by androgens and may be influenced by glucocorticoids and the frog’s social environment.

The frog preys on insects and is preyed upon by numerous fish and parasite species. To avoid predation, the species will often hide in its aquatic territory. It is not easily susceptible to chytridiomycosis and is a common backyard species and pet that requires undemanding conditions for care. It is the state amphibian of Georgia and Louisiana and can be used as bioindicators for aquatic contamination.

Description

With distended vocal sac

Many individuals of the American green tree frog are bright green and are of a streamlined and slender build. The American green tree frog is moderately sized. They have long legs, smooth skin, and bilateral symmetry. The size of the American green tree frog ranges from 3.2 to 6.4 centimetres (1+1⁄4 to 2+1⁄2 in) in length. Their dorsum can range in color from bright green to reddish-brown. Such a range in coloration accounts for false encounters of the frog by other species.[2][3]

The dorsum is peppered with small golden spots, and the frogs have a white to cream coloration on their ventral side. American green tree frogs also contain white prominent lateral stripes and are normally ectothermic and heterothermic amphibians. [4]

The American green tree frogs weigh on average 3.76g in mass with a range between 2.15g to 5.11g. Female frogs are usually larger than males. Larger males tend to have an upper hand in attracting females than smaller males either through increased physical strength in duels or more pronounced call signals during mating competition.[5]

Distribution and habitat

The American green tree frog is found in the central and southeastern United States with a geographic range from the Eastern Shore of Maryland to southeast Florida with populations as far west as central Texas and as far north as Delaware and southern New Jersey. The American green tree frog is considered monotypic, but clinal variation has beven observed from Florida north along the Atlantic coastal plain. This may be attributed to the result of strong selection and/or drift.[4]

American green tree frogs prefer to live in open canopy forests and permanent waters filled with plentiful vegetation. The species is found in natural and settled environments. The species commonly resides in cypress ponds, water lily prairies, and marshes. It is often found on twigs, low branches, and grasses.[6]

Conservation

A growing number of American green tree frogs have experienced severe habitat loss primarily due to urbanization and destructive wildfires. Wildfires in particular remove forest canopy covers. Since most amphibians have narrow habitat tolerances and migration constraints, American green tree frogs urgently need alternative shelter for survival as forest canopies recover. In a study from Central Texas, scientists have tried to combat wildfire habitat loss by creating artificial shelters using polyvinyl chloride pipes.[6]

Home Range and Territoriality

American green tree frogs will defend their mate calling sites against foreign rivals and invaders using aggressive interactions. Such behaviors include a combination of aggressive call signals and wrestling from males.[7]

Behavior

Male Dryophytes cinereus calling

Because the frog is small and easily frightened, it often does not do well with frequent handling. Some specimens do seem to tolerate it occasionally, so handling frequency should be determined on an individual basis. The American green tree frog tends to be nocturnal, and in captivity, it will be the most active once the lights are off. Males frequently call most of the year, especially after being misted in the tank.[8]

Breeding

Pair breeding
Tadpole
Metamorph
American green tree frogs vary in color.

Most American green tree frog females breed once per year, but some have multiple clutches in a single mating season. In a Florida population, "advertisement calls of males were documented between March and September and pairs in amplexus were observed between April and August". In the Florida population, the average number of eggs in a single clutch was observed to be about 400. Eggs take between four and 14 days to hatch, with an average of five days. According to the Animal Diversity Web at the University of Michigan Museum of Zoology, "Female size was positively correlated with clutch size, but after the initial clutch, the number of eggs nearly always decreased".[4]

Tadpoles are green with a yellow or white stripe extending from each nostril to the eye and may have mottled tail fins.[9] American green tree frogs show only the parental investment of mating and egg-laying.[4]

Breeding is known to be strongly influenced by day length, temperature, and precipitation. While the influence of these factors with respect to breeding is not well understood, it is known to exist, as the frogs generally breed following rainfall, and males call more frequently as temperature and day length increase. Some evidence demonstrates that the length of the breeding season is correlated with latitude, with seasonal length decreasing as latitude increases due to temperature limitations.[4]

Mating Calls

To attract mates, the male American green tree frog uses a distinctive advertisement call which is noticeably different from its release or warning calls. Once a mate has been attracted, the pair begins amplexus in which the male frog grasps onto the female to initiate fertilization. The species is polygynous, with the male generally seeking to mate with as many females as it can attract.[4] Eggs are attached to substrates such as emergent vegetation, and unlike with many other frog species, these egg masses are typically laid in permanent bodies of water rather than seasonal vernal pools.[10]

In the presence of many male frogs however, choruses will form and establish a cacophony of numerous acoustically different advertisement calls. Consequently, male individuals experience intraspecific mating competition and often encounter immense pressure to produce unique call signals that are both attractive and audible to a limited number of available females. Such challenges are further complicated by the rapid fluctuation of males within a chorus, the potential risk of increased exposure to predators, and sexual selection of specific call signals through female choice.[11]

These factors give rise to a social plasticity in the calling behavior of the American green tree frog. In order to maintain competition, male individuals will either modify their signal features such as the temporal and spectral properties of calls or their signal timing to reduce signal interference with other neighboring males. Temporal and spectral properties include call duration and call frequency. Changes in signal timing include initiating advertisement calls during different times at night. It has been found that male green tree frogs will more often alter their signal timing to attract females due to physiological constraints in the frog’s call production mechanism and female choice against increased call duration and period in favor of precise call timing. Modifying signal behavior towards every frog within a chorus is extremely costly and inefficient. However, forcing male individuals to engage in selective attention of advertisement calls from only a few of their closest rivals.[11]

Some male American green tree frogs will not emit or alter their advertisement calls and instead choose to remain silent. Labeled as 'satellites', these frogs will wait to intercept the signals of nearby calling males and mate with approaching sexually active females through amplexus. Such sexual parasitism and call avoidance occur mainly to conserve the frog’s energy and avoid predation during mate competition.[12]

Androgens are used for energy during call signal production. As a satellite male green tree frog engages in non-calling mating behavior, androgen quantities are found to decrease to lower levels compared to calling behavior, suggesting a causal relationship between sex hormones and mate calling tactics.[7]

In order to help decide whether to engage in satellite non-calling behavior, male green tree frogs will eavesdrop on other nearby male competitors and adjust their mating responses based on the qualities of their call signals. If faced with a choice, females will prefer large males with advertisement calls of lower frequencies. Other notable features include the latency to call and male focal size. When eavesdropping male competitors with low call frequencies, large male green tree frogs are found to reduce their latency to call and raise call rates. Small males in contrast will only reduce their latency to call in response to competitors with average call frequencies.[5]

American green tree frogs are also able to undergo interspecific mating competition. In southern Florida, the Cuban tree frog (Osteopilus septentrionalis) is an invasive species that has a similar call to the American green tree frog with respect to timing and pitch. A study found that their calls compete acoustically with each other due to their similarity which limits communication space. In order to compete with the Cuban tree frog, American green tree frogs modified their calls to be shorter, louder, and more frequent so that potential mates would have a better chance of detecting the call.[13][14]

Feeding

American green tree frogs are insectivores, usually consuming flies, mosquitoes, and other small insects such as crickets. One study suggested the frog selects prey not by its size, but according to its activity level, with the most active prey being the most frequently eaten. The same study showed "nearly 90% of Hyla cinerea prey were actively pursued", with the other 10% being "insects walking or close enough to be snatched up by the frog's tongue".[4]

Enemies

As a tadpole, the American green tree frog is easily predated by sunfish, bass, and dragonflies, including both aeshnidae and libellulidae odonate naiads. The species is especially vulnerable to predation when living in temporary ponds compared to permanent waters. To combat increased predation, green tree frog tadpoles may increase hiding behavior while in water to avoid capture.[15][16]

The American green tree frog is also prone to a few parasites, including nematodes, protozoans, and trematodes.[17]

Contrary to most amphibians, the American green tree frog is not easily susceptible to the Batrachochytrium dendrobatidis (Bd) pathogen and the disease chytridiomycosis. Reasons explaining why are relatively unknown, but one study hypothesizes that variances in climate, frog immunity, and frog habitat are potential factors.[18]

Physiology

Androgens

Androgens, such as dihydrotestosterone and testosterone, are the primary energy resource for American green tree frogs when engaging in acoustic signal calling. When a male frog engages in vocalization either for aggression or mate attraction, androgen energy stores are used and become depleted. Interestingly, glucocorticoids, such as corticosterones, also appear to change during calling behavior. According to the Energetics-Hormone Vocalization model, glucocorticoid levels in males will rise as androgen levels decrease following vocalization. When observing hormonal levels in both calling and satellite non-calling males, reduced androgen levels and elevated glucocorticoid levels are found among satellite non-calling males compared to calling males. These observations suggest a possible mechanism dictating vocalization and the alternation between calling and non-calling behavior in the green tree frog. Further study is required however on the relationship between glucocorticoids and male vocalization to consider causality.[7]

The causality of vocalization by androgens is also limited by the American green tree frog’s social environment. According to one study, androgens themselves were not sufficient to initiate call signals in male frogs when in the presence of social stimuli such as other frog choruses. This suggests that androgens on their own may provide males with enough motivation to call, but they may also require additional social context to produce various call signals during situations such as mating.[19]

As pets

American green tree frogs are popular pets because of their small size, appearance, and the undemanding conditions needed to take care of them. Unlike many amphibians, they do not require artificial heating unless household temperatures drop below 21 °C (70 °F). They need a large (at least ten-gallon) terrarium and do best with a substrate that will hold some humidity, such as commercial shredded bark or coconut husk bedding, or untreated topsoil on the floor of the terrarium. Tree frogs are arboreal, so the height of the tank is more important than the length. A variety of things for climbing, such as plants or branches, should be in the habitat. A shallow water dish should be included. Captive frogs should not be handled more than necessary; when necessary, clean gloves should be worn.[20]

As state symbols and bioindicators

The American green tree frog became the state amphibian of Louisiana in 1997[21] and of Georgia in 2005.[22][23]

American green tree frogs can also be used as bioindicators for aquatic contamination. Synthetic compounds such as polychlorinated biphenyls are found in many pesticides and pollute the green tree frog’s aquatic habitats. Because the frog’s skin is thin and permeable, synthetic compounds absorb easily upon contact, making the species a viable variable to measure contamination.[24]

References

  1. ^ Hammerson, G.A.; Hedges, B. (2017), "Dryophytes cinereus", IUCN Red List of Threatened Species, 2017: e.T55449A112713111, doi:10.2305/IUCN.UK.2017-1.RLTS.T55449A112713111.en, retrieved 2021-11-12
  2. ^ Pham, Lanminh; Boudreaux, Seth; Karhbet, Sam; Price, Becky; Ackleh, Azmy S.; Carter, Jacoby; Pal, Nabendu (June 2007). "Population Estimates of Hyla cinerea (Schneider) (Green Tree Frog) in an Urban Environment". Southeastern Naturalist. 6 (2): 203–216. doi:10.1656/1528-7092(2007)6[203:PEOHCS]2.0.CO;2. ISSN 1528-7092.
  3. ^ Lodato, M. J., Engbrecht, N. J., Klueh-Mundy, S., & Walker, Z. (2014). The Green Treefrog, Hyla cinerea (Schneider), in Indiana. Proceedings of the Indiana Academy of Science, 123(2), Article 2.
  4. ^ a b c d e f g Nichols, Matthew (2008), "Hyla cinerea (green treefrog)]", University of Michigan Museum of Zoology, archived from the original on 2022-09-29, retrieved 2022-09-29
  5. ^ a b Garcia, Mark J.; Cronin, Andrew; Bowling, Tyler; Bushera, Hakeem; Hunter, Kimberly L.; Taylor, Ryan C. (2019-01-25). "Dueling frogs: do male green tree frogs (Hyla cinerea) eavesdrop on and assess nearby calling competitors?". Behavioral Ecology and Sociobiology. 73 (2): 21. doi:10.1007/s00265-018-2632-1. ISSN 1432-0762.
  6. ^ a b Suriyamongkol, Thanchira; Forks, Kaitlyn; Villamizar-Gomez, Andrea; Wang, Hsiao-Hsuan; Grant, William E.; Forstner, Michael R. J.; Mali, Ivana (December 2021). "A Simple Conservation Tool to Aid Restoration of Amphibians following High-Severity Wildfires: Use of PVC Pipes by Green Tree Frogs (Hyla cinerea) in Central Texas, USA". Diversity. 13 (12): 649. doi:10.3390/d13120649. ISSN 1424-2818.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  7. ^ a b c Leary, Christopher J.; Harris, Samuel (2013-01-01). "Steroid hormone levels in calling males and males practicing alternative non-calling mating tactics in the green treefrog, Hyla cinerea". Hormones and Behavior. 63 (1): 20–24. doi:10.1016/j.yhbeh.2012.11.006. ISSN 0018-506X.
  8. ^ "Green Tree Frog", lllreptile.com, archived from the original on 2015-11-08, retrieved 2016-04-25
  9. ^ Somma, L.A. (2018-05-03), "Dryophytes cinereus (Schneider, 1799)", U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, USA, archived from the original on 2022-09-29, retrieved 2022-09-29
  10. ^ Garton, John S.; Brandon, Ronald A. (1975), "Reproductive Ecology of the Green Treefrog, Hyla cinerea, in Southern Illinois (Anura: Hylidae)", Herpetologica, 31 (2): 150–161, ISSN 0018-0831
  11. ^ a b Neelon, Daniel P.; Höbel, Gerlinde (2019-08-13). "Staying ahead of the game—plasticity in chorusing behavior allows males to remain attractive in different social environments". Behavioral Ecology and Sociobiology. 73 (9): 124. doi:10.1007/s00265-019-2737-1. ISSN 1432-0762.
  12. ^ Perrill, S. A., Gerhardt, H. C., & Daniel, R. (1978). Sexual Parasitism in the Green Tree Frog (Hyla cinerea). Science, 200(4346), 1179–1180.
  13. ^ Bates, Mary (2016-04-25), "Invasive Species Compete With Native Species For Room To Be Heard Archived 2018-04-29 at the Wayback Machine", PLOS Ecology Community
  14. ^ Tennessen, Jennifer B.; Parks, Susan E.; Tennessen, Travis P.; and Langkilde, Tracy (2016), "Raising a Racket: Invasive Species Compete Acoustically with Native Treefrogs", Animal Behaviour 114 (2016): 53–61
  15. ^ Gunzburger, Margaret S. (December 2005). "Differential Predation on Tadpoles Influences the Potential Effects of Hybridization between Hyla cinerea and Hyla gratiosa". Journal of Herpetology. 39 (4): 682–687. doi:10.1670/226-04N.1. ISSN 0022-1511.
  16. ^ Gunzburger, M S; Travis, J (2005-07-01). "Effects of multiple predator species on green treefrog ( Hyla cinerea ) tadpoles". Canadian Journal of Zoology. 83 (7): 996–1002. doi:10.1139/z05-093. ISSN 0008-4301.
  17. ^ Creel, Foster (2000). "Parasites of the Green Treefrog, Hyla cinerea, from Orange Lake, Alachua County, Florida, U.S.A.". Comparative Parasitology. 67 (2): 255–258.
  18. ^ Brannelly, Laura A.; Chatfield, Matthew W. H.; Richards-Zawacki, Corinne L. (2012-06-07). "Field and Laboratory Studies of the Susceptibility of the Green Treefrog (Hyla cinerea) to Batrachochytrium dendrobatidis Infection". PLOS ONE. 7 (6): e38473. doi:10.1371/journal.pone.0038473. ISSN 1932-6203. PMC 3369911. PMID 22685572.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  19. ^ Burmeister, Sabrina S.; Wilczynski, Walter (2001-12-01). "Social Context Influences Androgenic Effects on Calling in the Green Treefrog (Hyla cinerea)". Hormones and Behavior. 40 (4): 550–558. doi:10.1006/hbeh.2001.1723. ISSN 0018-506X.
  20. ^ McLeod, Lianne, "American Green Tree Frogs as Pets", thesprucepets.com, archived from the original on 2022-09-29, retrieved 2022-09-29
  21. ^ "RS 49:169.1", legis.la.gov, Louisiana State Legislature, retrieved 2019-05-07
  22. ^ "§ 50-3-81—Official amphibian", 2017 Georgia Code, retrieved 2019-05-07
  23. ^ Broady, Arlinda Smith (2015-05-06), "Photo Vault: Push for a state amphibian became life lesson for kids", Atlanta Journal-Constitution, retrieved 2019-05-07
  24. ^ DeGarady, Colette J.; Halbrook, Richard S. (March 2006). "Using Anurans as Bioindicators of PCB Contaminated Streams". Journal of Herpetology. 40 (1): 127–130. doi:10.1670/30-05N.1. ISSN 0022-1511.

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