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Wood frog

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Wood frog
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Order: Anura
Family: Ranidae
Genus: Lithobates
Species:
L. sylvaticus
Binomial name
Lithobates sylvaticus
(LeConte, 1825)
Geographic range of the wood frog in North America (in blue)
Synonyms
  • Rana sylvatica
    LeConte, 1825

Lithobates sylvaticus[1][2] or Rana sylvatica,[3] commonly known as the wood frog, is a frog species that has a broad distribution over North America, extending from the boreal forest of the north to the southern Appalachians, with several notable disjunct populations including lowland eastern North Carolina. The wood frog has garnered attention from biologists because of its freeze tolerance, relatively great degree of terrestrialism (for a ranid), interesting habitat associations (peat bogs, vernal pools, uplands), and relatively long-range movements.

The ecology and conservation of the wood frog has attracted research attention in recent years because they are often considered "obligate" breeders in ephemeral wetlands (sometimes called "vernal pools"), which are themselves more imperiled than the species that breed in them. The wood frog has been proposed to be the official state amphibian of New York.[4]

Description

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Wood frog demonstrating lighter skin tones, New Jersey Pine Barrens

Wood frogs range from 51 to 70 mm (2.0 to 2.8 in) in length. Females are larger than males.[5][6] Adult wood frogs are usually brown, tan, or rust-colored, and usually have a dark eye mask.[7] Individual frogs are capable of varying their color; Conant (1958) depicts one individual which was light brown and dark brown at different times. The underparts of wood frogs are pale with a yellow or green cast;[8] in northern populations, the belly may be faintly mottled. Their body colour may change seasonally; exposure to sunlight causes darkening.[9]

Showing ground leaf camouflage pattern, Darien Lakes State Park
Showing dark skin tones, Mer Bleue Conservation Area
Depicting a pinkish-tan skin tone, White Clay Creek

Geographic range

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The contiguous wood frog range is from northern Georgia and northeastern Canada in the east to Alaska and southern British Columbia in the west.[10] They range all throughout the boreal forests of Canada. [11] It is the most widely distributed frog in Alaska. It is also found in the Medicine Bow National Forest.

Habitat

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Wood frogs are forest-dwelling organisms that breed primarily in ephemeral, freshwater wetlands: woodland vernal pools. They are nonarboreal and spend most of their time of the forest floor.[12] Long-distance migration plays an important role in their life history. Individual wood frogs range widely (hundreds of metres) among their breeding pools and neighboring freshwater swamps, cool-moist ravines, and/or upland habitats. Genetic neighborhoods of individual pool breeding populations extend more than a kilometre away from the breeding site. Thus, conservation of this species requires a landscape (multiple habitats at appropriate spatial scales) perspective. They also can be camouflaged with their surroundings.

Spring mating calls

A study was done on wood frogs dispersal patterns in 5 ponds at the Appalachian Mountains where they reported adult wood frogs were 100% faithful to the pond of their first breeding but 18% of juveniles dispersed to breed in other ponds.[13]

Adult wood frogs spend summer months in moist woodlands, forested swamps, ravines, or bogs. During the fall, they leave summer habitats and migrate to neighboring uplands to overwinter. Some may remain in moist areas to overwinter. Hibernacula tend to be in the upper organic layers of the soil, under leaf litter. By overwintering in uplands adjacent to breeding pools, adults ensure a short migration to thawed pools in early spring. Wood frogs are mostly diurnal and are rarely seen at night, except maybe in breeding choruses. They are one of the first amphibians to emerge for breeding right when the snow melts, along with spring peepers.

Feeding

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Picture of a wood frog on the shoreline of Kabekona Lake, Minnesota

Wood frogs eat a variety of small, forest-floor invertebrates, with a diet primarily consisting of insects. The tadpoles are omnivorous, feeding on plant detritus and algae along with other tadpoles of their own and other species.[14]

The feeding pattern of the wood frog is similar to that of other ranids. It is triggered by prey movement and consists of a bodily lunge that terminates with the mouth opening and an extension of the tongue onto the prey.[15] The ranid tongue is attached to the floor of the mouth near the tip of the jaw, and when the mouth is closed, the tongue lies flat, extended posteriorly from its point of attachment.

In the feeding strike, the tongue is swung forward as though on a hinge, so some portion of the normally dorsal and posterior tongue surface makes contact with the prey. At this point in the feeding strike, the wood frog differs markedly from more aquatic Lithobates species, such as the green frog, leopard frog, and bullfrog.[15] The wood frog makes contact with the prey with just the tip of its tongue, much like a toad.[16] A more extensive amount of tongue surface is applied in the feeding strikes of these other frog species, with the result that usually the prey is engulfed by the fleshy tongue and considerable tongue surface contacts the surrounding substrate.

Cold tolerance

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Lithobates sylvaticus found in southern Quebec
See also: Moor frog and Cryobiology

Similar to other northern frogs that enter dormancy close to the surface in soil and/or leaf litter, wood frogs can tolerate the freezing of their blood and other tissues.[17][18] Urea is accumulated in tissues in preparation for overwintering,[citation needed] and liver glycogen is converted in large quantities to glucose in response to internal ice formation. Both urea and glucose act as cryoprotectants to limit the amount of ice that forms and to reduce osmotic shrinkage of cells.[19][20] Frogs found in southern Canada and the American midwest can tolerate freezing temperatures of −3 to −6 °C (27 to 21 °F). However, wood frogs in Interior Alaska exhibit even greater tolerance, with some of their body water freezing while still surviving. Wood frogs in natural hibernation remain frozen for 193 +/- 11 consecutive days and reached an average (October–May) temperature of −6.3 °C (20.7 °F) and an average minimum temperature of −14.6 ± 2.8 °C (5.7 ± 5.0 °F). The wood frog has evolved various physiological adaptations that allow it to tolerate the freezing of 65–70% of its total body water. When water freezes, ice crystals form in cells and break up the structure, so that when the ice thaws the cells are damaged. Frozen frogs also need to endure the interruption of oxygen delivery to their tissues as well as strong dehydration and shrinkage of their cells when water is drawn out of cells to freeze. The wood frog has evolved traits that prevent their cells from being damaged when frozen and thawed out. The wood frog has developed various adaptations that allow it to effectively combat prolonged ischemia/anoxia and extreme cellular dehydration. One crucial mechanism utilized by the wood frog is the accumulation of high amounts of glucose that act as a cryoprotectant.[21]

Frogs can survive many freeze/thaw events during winter if no more than about 65% of the total body water freezes. Wood frogs have a series of seven amino acid substitutions in the sarco/endoplasmic reticulum Ca2+-ATPase 1 (SERCA 1) enzyme ATP binding site that allows this pump to function at lower temperatures relative to less cold-tolerant species (e.g. Lithobates clamitans).[22]

Studies on northern subpopulations found that Alaskan wood frogs had a larger liver glycogen reserve and greater urea production[23] compared to those in more temperate zones of its range. These conspecifics also showed higher glycogen phosphorylase enzymatic activity, which facilitates their adaptation to freezing.[24]

The phenomenon of cold resistance is observed in other anuran species. The Japanese tree frog shows even greater cold tolerance than the wood frog, surviving in temperatures as low as −35 °C (−31 °F) for up to 120 days.[25]

Reproduction

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Tadpole

L. sylvaticus primarily breeds in ephemeral pools rather than permanent water bodies such as ponds or lakes.[26] This is believed to provide some protection for the adult frogs and their offspring (eggs and tadpoles) from predation by fish and other predators of permanent water bodies. Adult wood frogs typically hibernate within 65 meters of breeding pools.[12] They emerge from hibernation in early spring and migrate to the nearby pools. There, males chorus, emitting duck-like quacking sounds.

Wood frogs are considered explosive breeders; many populations will conduct all mating in the span of a week.[27] Males actively search for mates by swimming around the pool and calling. Females, on the other hand, will stay under the water and rarely surface, most likely to avoid sexual harassment.[28] A male approaches a female and clasps her from behind her forearms before hooking his thumbs together in a hold called "amplexus", which is continued until the female deposits the eggs.[6][26] Females deposit eggs attached to submerged substrate, typically vegetation or downed branches. Most commonly, females deposit eggs adjacent to other egg masses, creating large aggregations of masses.[6][26][29]

Some advantage is conferred to pairs first to breed, as clutches closer to the center of the raft absorb heat and develop faster than those on the periphery, and have more protection from predators.[6][26] If pools dry before tadpoles metamorphose into froglets, they die.[6] This constitutes the risk counterbalancing the antipredator protection of ephemeral pools. By breeding in early spring, however, wood frogs increase their offspring's chances of metamorphosing before pools dry.

The larvae undergo two stages of development: fertilization to free-living tadpoles, and free-living tadpoles to juvenile frogs.[30][31] During the first stage, the larvae are adapted for rapid development, and their growth depends on the temperature of the water.[31][32] Variable larval survival is a major contributor to fluctuations in wood frog population size from year to year.[32] The second stage of development features rapid development and growth, and depends on environmental factors including food availability, temperature, and population density.[31]

Some studies suggest that road-salts, as used in road de-icing, may have toxic effects on wood frog larvae. A study exposed wood frog tadpoles to NaCl and found that tadpoles experienced reduced activity and weight, and even displayed physical abnormalities. There was also significantly lower survivorship and decreased time to metamorphosis with increasing salt concentration. De-icing agents may pose a serious conservation concern to wood frog larvae.[33] Another study has found increased tolerance to salt with higher concentrations, though the authors caution against over-extrapolating from short-term, high concentration studies to longer-term, lower concentration conditions, as contradictory outcomes occur.[34]

Following metamorphosis, a small percentage (less than 20%) of juveniles will disperse, permanently leaving the vicinity of their natal pools. The majority of offspring are philopatric, returning to their natal pool to breed.[30] Most frogs breed only once in their lives, although some will breed two or three times, generally with differences according to age.[26][30][35] The success of the larvae and tadpoles is important in populations of wood frogs because they affect the gene flow and genetic variation of the following generations.[30]

Conservation status

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Although the wood frog is not endangered or threatened, in many parts of its range, urbanization is fragmenting populations. Several studies have shown, under certain thresholds of forest cover loss or over certain thresholds of road density, wood frogs and other common amphibians begin to "drop out" of formerly occupied habitats. Another conservation concern is that wood frogs are primarily dependent on smaller, "geographically isolated" wetlands for breeding. At least in the United States, these wetlands are largely unprotected by federal law, leaving it up to states to tackle the problem of conserving pool-breeding amphibians.[1]

The wood frog has a complex lifecycle that depends on multiple habitats, damp lowlands, and adjacent woodlands. Their habitat conservation is, therefore, complex, requiring integrated, landscape-scale preservation.[1]

Wood frog development in the tadpole stage is known to be negatively affected by road salt contaminating freshwater ecosystems.[33] Tadpoles have also been shown to develop abnormalities due to a combination of warmer conditions and toxic metals from pesticides near their habitats. These conditions allow them to be predated upon by dragonfly larvae more easily often causing missing limbs.[36]

References

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  1. ^ a b c d IUCN SSC Amphibian Specialist Group (2015). "Lithobates sylvaticus". IUCN Red List of Threatened Species. 2015: e.T58728A78907321. doi:10.2305/IUCN.UK.2015-4.RLTS.T58728A78907321.en. Retrieved 19 February 2022.
  2. ^ Frost, Darrel R. (2022). "Lithobates sylvaticus (LeConte, 1825)". Amphibian Species of the World: An Online Reference. Version 6.1. American Museum of Natural History. doi:10.5531/db.vz.0001. Retrieved 10 March 2022.
  3. ^ Yuan, Z.-Y.; et al. (2016). "Spatiotemporal diversification of the true frogs (genus Rana): A historical framework for a widely studied group of model organisms". Systematic Biology. 65 (5): 824–42. doi:10.1093/sysbio/syw055. hdl:2292/43460. PMID 27288482.
  4. ^ "Senate backs the wood frog — barely". Politico. 17 June 2015.
  5. ^ Monnet J-M; Cherry MI (2002). "Sexual size dimorphism in anurans". Proceedings of the Royal Society B. 269 (1507): 2301–2307. doi:10.1098/rspb.2002.2170. PMC 1691160. PMID 12495496.
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  7. ^ Conant R, Collins JT. (1998). A field guide to reptiles & amphibians: eastern and central North America. Third edition. New York (NY): Houghton Mifflin Company ISBN 0395904528.
  8. ^ Conant, Roger. (1958). A Field Guide to Reptiles and Amphibians. Houghton Mifflin Company, Boston.
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  10. ^ Wilbur HM (1977). "Interactions of food level and population density in Rana sylvatica". Ecology. 58 (1): 206–209. Bibcode:1977Ecol...58..206W. doi:10.2307/1935124. JSTOR 1935124.
  11. ^ Fitzpatrick, Megan J., et al. “Future Winters present a complex energetic landscape of decreased costs and reduced risk for a freeze‐tolerant amphibian, the wood frog (lithobates sylvaticus).” Global Change Biology, vol. 26, no. 11, 24 Sept. 2020, pp. 6350–6362, https://doi.org/10.1111/gcb.15321.
  12. ^ a b Regosin, Jonathan V.; Windmiller, Bryan S.; Reed, J. Michael (2003). "Terrestrial Habitat Use and Winter Densities of the Wood Frog (Rana sylvatica)". Journal of Herpetology. 37 (2): 390–394. doi:10.1670/0022-1511(2003)037[0390:THUAWD]2.0.CO;2. ISSN 0022-1511. JSTOR 1566158.
  13. ^ Berven, Keith A., and Thaddeus A. Grudzien. "Dispersal in the wood frog (Rana sylvatica): implications for genetic population structure." Evolution 44.8 (1990): 2047-2056.
  14. ^ Redmer, Michael and Trauth, Stanley E. (2005). Amphibian Declines: The Conservation Status of United States Species M. Lannoo, ed. University of California Press ISBN 0520235924.
  15. ^ a b Cardini, F. (1974). Specializations of the Feeding Response of the Bullfrog, Rana catesbeiana, for the Capture of Prey Submerged in Water. M.S. Thesis, U. of Massachusetts, Amherst, MA
  16. ^ Cardini, F. (1973). Characteristics and Adaptedness of Feeding Behaviors of North American Anurans, Paper presented at June 1973 meetings of the Animal Behavior Society, Amherst, MA
  17. ^ Storey KB; Storey JM (1984). "Biochemical adaption for freezing tolerance in the wood frog, Rana sylvatica". Journal of Comparative Physiology B. 155: 29–36. doi:10.1007/BF00688788. S2CID 29760226.
  18. ^ Wilbur HM (1997). "Experimental ecology of food webs: complex systems in temporary ponds". Ecology. 78 (8): 2279–2302. doi:10.1890/0012-9658(1997)078[2279:EEOFWC]2.0.CO;2.
  19. ^ Kenneth B. Storey (1997). "Organic solutes in freezing tolerance". Comparative Biochemistry and Physiology A. 117 (3): 319–326. doi:10.1016/s0300-9629(96)00270-8. PMID 9172388.
  20. ^ Costanzo JP; Lee RE Jr.; DeVries AL; Wang T; Layne JR Jr. (1995). "Survival mechanisms of vertebrate ectotherms at subfreezing temperatures: applications in cryomedicine". The FASEB Journal. 9 (5): 351–358. doi:10.1096/fasebj.9.5.7896003. PMID 7896003. S2CID 13484261.
  21. ^ Bansal, Saumya (2016). "MicroRNA Regulation in Heart and Skeletal Muscle over the Freeze–thaw Cycle in the Freeze Tolerant Wood Frog". Journal of Comparative Physiology B. 186 (2, Springer Berlin Heidelberg, 2015): 229–41. doi:10.1007/s00360-015-0951-3. PMID 26660652. S2CID 16490101.
  22. ^ Dode, L; Van Baelen, K; Wuytack, F; Dean, WL (2001). "Low temperature molecular adaptation of the skeletal muscle sarco(endo)plasmic reticulum Ca2+-ATPase 1 (SERCA 1) in the wood frog (Rana sylvatica)". Journal of Biological Chemistry. 276 (6): 3911–9. doi:10.1074/jbc.m007719200. PMID 11044449.
  23. ^ Costanzo, Jon P.; Do Amaral, M. Clara F.; Rosendale, Andrew J.; Lee, Richard E. (2013). "Hibernation physiology, freezing adaptation and extreme freeze tolerance in a northern population of the wood frog". Journal of Experimental Biology. 216 (18): 3461–3473. doi:10.1242/jeb.089342. PMID 23966588. Retrieved 2024-03-29.
  24. ^ Amaral, M. Clara F. do; Lee, Richard E.; Costanzo, Jon P. (November 2013). "Enzymatic Regulation of Glycogenolysis in a Subarctic Population of the Wood Frog: Implications for Extreme Freeze Tolerance". PLOS ONE. 8 (11): e79169. Bibcode:2013PLoSO...879169D. doi:10.1371/journal.pone.0079169. PMC 3827335. PMID 24236105. ProQuest 1458261108.
  25. ^ Berman, D. I.; Meshcheryakova, E. N.; Bulakhova, N. A. (Jan 2016). "The Japanese tree frog (Hyla japonica), one of the most cold-resistant species of amphibians". Doklady Biological Sciences. 471 (1): 276–279. doi:10.1134/s0012496616060065. PMID 28058600. S2CID 254413388.
  26. ^ a b c d e Berven KA (1981). "Mate choice in the wood frog, Rana sylvatica". Evolution. 35 (4): 707–722. doi:10.2307/2408242. JSTOR 2408242. PMID 28563133.
  27. ^ Kats, L.B., J.W. Petranka, and A. Sih. 1988. Antipredator defenses and the persistence of amphibian larvae with fishes. Ecology 69:1865–1870.
  28. ^ Hobel, Gerlinde (2013). "Wood frogs (Lithobates sylvaticus) use water surface waves in their reproductive behaviour". Behaviour. 150 (5): 471–483. doi:10.1163/1568539X-00003062.
  29. ^ Seale DB (1982). "Physical factors influencing oviposition by the woodfrog, Rana sylvatica, in Pennsylvania". Copeia. 1982 (3): 627–635. doi:10.2307/1444663. JSTOR 1444663.
  30. ^ a b c d Berven KA; Grudzien TA (1990). "Dispersal in the wood frog (Rana sylvatica): implications for genetic population structure". Evolution. 44 (8): 2047–2056. doi:10.2307/2409614. JSTOR 2409614. PMID 28564421.
  31. ^ a b c Herreid CF II; Kinney S (1967). "Temperature and development of the wood frog, Rana sylvatica, in Alaska". Ecology. 48 (4): 579–590. Bibcode:1967Ecol...48..579H. doi:10.2307/1936502. JSTOR 1936502.
  32. ^ a b Berven KA (1990). "Factors affecting population fluctuation in larval and adult stages of the wood frog (Rana sylvatica)". Ecology. 71 (4): 1599–1608. Bibcode:1990Ecol...71.1599B. doi:10.2307/1938295. JSTOR 1938295.
  33. ^ a b Sanzo, Domenico; Hecnar, Stephen J. (March 2006). "Effects of road de-icing salt (NaCl) on larval wood frogs (Rana sylvatica)". Environmental Pollution. 140 (2): 247–256. Bibcode:2006EPoll.140..247S. doi:10.1016/j.envpol.2005.07.013. PMID 16159689.
  34. ^ Relyea, Rick; Mattes, Brian; Schermerhorn, Candace; Shepard, Isaac (2024-03-12). "Freshwater salinization and the evolved tolerance of amphibians". Ecology and Evolution. 14 (3): e11069. Bibcode:2024EcoEv..1411069R. doi:10.1002/ece3.11069. ISSN 2045-7758. PMC 10933534. PMID 38481759.
  35. ^ Berven KA (1988). "Factors affecting variation in reproductive traits within a population of wood frogs (Rana sylvatica)". Copeia. 1988 (3): 605–615. doi:10.2307/1445378. JSTOR 1445378.
  36. ^ Reeves, Mari K.; Jensen, Peter; Dolph, Christine L.; Holyoak, Marcel; Trust, Kimberly A. (August 2010). "Multiple stressors and the cause of amphibian abnormalities". Ecological Monographs. 80 (3): 423–440. Bibcode:2010EcoM...80..423R. doi:10.1890/09-0879.1. ISSN 0012-9615.

Further reading

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