Natural History: Wood frogs are cold weather specialists, able to be found as far north as Nunavut, the Yukon and Alaska. As winter approaches and temperatures begin to drop, these frogs will change colour, becoming dark in colder temperatures to absorb more heat from the sun. When temperatures drop, many frogs seek out wetlands, where they will live underwater, below the point of freezing. Wood frogs however, don’t make it to these wetlands and seek refuge under logs or leaf litter, here they freeze solid. This would kill most animals as it would cause the cells to die from desiccation. For the wood frog however, they produce a natural antifreeze made up of glucose synthesized in the liver, this helps protect the frogs’ cells from desiccation. Within this frozen state, ice forms between the frog’s cells, their blood stops pumping and they become a solid, brittle mass. Triggered by warm temperatures, wood frogs can make a fast recovery from their state of suspended animation, with the heart beating again while ice still exists within the body. Within hours, the frog regains motor control and starts behaving normally again after only 24 hours. Their drive to mate however may take up to a week to recover.
|
Anatomy: Frogs such as wood frogs are able to hear through a variety of different methods; high pitched noises are picked up through the frog’s tympanum which acts like an external ear drum behind the eyes. This is used when listening for the calls of other frogs. To hear low frequency noise, frogs are able to pick up vibrations from the ground and water. The vibrations travel up the scapula bone in their legs to the operculum-columella, part of their inner ear. Hearing these low pitched noises is especially useful when detecting potential predators or prey
|
Reproduction: Wood frogs are explosive breeders, come spring, males emerge from their dormancy and make their way to breeding ponds free of fish. Females soon arrive but in small numbers, these early females are often swarmed by eager males who all attempt to breed with her. Males will often form breeding balls around the female who have been known to drown from this. As more females arrive, the breeding balls die down. Males attract the female with a call described as being similar to a duck call and amplified by their paired lateral sacks. When a female comes close, the male will grab onto her in amplexus so that when she lays her eggs, he can fertilize them externally. An individual wood frogs can lay up to 870 eggs at a time which are often added to a raft of other eggs. By having so many together, it can increase the amount of solar rays Absorbed, increasing temperature and speeding up development. Tadpoles soon hatch and can be better identified as they get larger. Wood frog tadpoles are dark bodied, often with a dark mask through the eye, mottled tail fins and a bi-coloured musculature on the tail.
|
Sources:
Costanzo, Jon P., et al. "Glucose Concentration Regulates Freeze Tolerance in the Wood Frog Rana sylvatica." Research Gate, Journal of Experimental Biology, Sept. 1993, www.researchgate.net/publication/14789136_Glucose_concentration_regulates_freeze_tolerance_in_the_wood_frog_Rana_sylvatica. Accessed 4 Nov. 2021. Fridgen, Tina. "Herpetology BIOL3340H Amphibian Biology." Trent University, 17 Sept. 2019, Peterborough, Canada. Lecture. Mills, Peter B. Metamorphosis. self-published, 2016, pp. 92-96. "Wood Frog." Ontario Nature, 2021, ontarionature.org/programs/community-science/reptile-amphibian-atlas/wood-frog/. Accessed 4 Nov. 2021. |