What frogs go through for their tadpoles

by Greg Mayer

Matthew has once again given me a hot tip: the BBC has a video of a mountain chicken, Leptodactylus fallax, feeding its developing tadpoles with unfertilized eggs. (I am unable to embed the video– do click through to watch). The mountain chicken is actually a large frog (so named because they are good eating– many years ago an attempt was made to establish the species in Puerto Rico as a food source) that is found on the eastern Caribbean islands of Montserrat and Dominica, and formerly Martinique.

Feeding unfertilized eggs to tadpoles may seem like a bizarre and exotic way to take care of your offspring (the BBC labeled it an “alien scene”), but it’s actually sort of mundane in the world of amphibians. Amphibians have the most diverse set of modes of reproduction and nutrition of juveniles of all the land vertebrates. Laurie Vitt and Janalee Caldwell, in their superb herpetology textbook, list 40 different reproductive modes for frogs. Its hard to pick a strangest amphibian reproductive mode, but I’d go with either the gastric-brooding frog, Rheobatrachus silus, in which the female swallows her eggs, which develop in her stomach, or histophagy, practiced by several amphibians, in which the fetuses feed upon the mother’s hypertrophied oviductal lining (i.e. while still inside of her).

The poison dart frog, Dendrobates auratus, above is a male, carrying a single tadpole in the lower middle of its back, which it will transport to some wet spot, such as a puddle or tree hole. The female of its relative Dendrobatus pumilio (featured in a previous post) places its tadpoles in the axils of bromeliads or other arboreal plants, and then returns, like the mountain chicken, to feed them with unfertilized eggs.

The pair of tree frogs, Hyla phlebodes, above was found in amplexus (that’s what mating is called in frogs); the male is the smaller one. Unlike the other frogs mentioned in this post, this species has the typical, un-exotic reproductive mode for frogs: eggs are laid in the water, which hatch into tadpoles, which metamorphose into froglets. It’s a pretty wondrous way of life, too, it just seems a bit un-exotic because we’ve been jaded by its familiarity.

Many amphibians have recently undergone significant population declines, and a number of species, including the gastric-brooding frog are now extinct. A fungal disease called chytridiomycosis has been implicated in causing the decline of many species, including the mountain chicken. The BBC video was made as part of a captive breeding conservation effort involving the Jersey Zoo, founded by the late naturalist and author Gerald Durrell,and the London Zoo.