This cute little frog might not look extraordinary in any particular way, but it has one of the strangest reproductive behaviors in the world. The Darwin’s frog exists as two separate species: The Chile Darwin’s frog (Rhinoderma rufum) and the Southern Darwin’s frog (R. darwinii). Like many other frogs, Darwin’s frogs live in the damp litter of the temperate forest floor within their habitat range and feed on small insects. The frogs’ backs vary greatly in coloring and come in pale green, dark green, tan, reddish brown, dark brown, and several other different shades. All of them have cream colored bellies with black blotches of differing size. Chile Darwin’s frogs are found only in Chile, as the name suggests, from Curico to Araouco Province. The Southern Darwin’s frog occurs in central and south Chile as well as nearby areas of Argentina. Both species are on the decline, but the Chile Darwin’s frog is more so and is listed as a critically endangered species in the IUCN Red List of Threatened Species. It may already be extinct, as the last recorded sighting was in 1980. Reasons for the decline of these frogs ranges from habitat loss to a devastating fungal disease, chytridiomycosis (caused by the Batrachochytrium dendrobatidis fungus), that is particularly destructive to amphibians.
A frog killed by chytridiomycosis. Taken by Brian Gratwicke on Flickr.
Two different color morphs of R. darwinii: First photo by Flavio Camus and second by Efe, both from Flickr.
What makes these two frog species so unusual and unique among animals is the fact that the tadpoles develop inside the male frog’s vocal sac. After the female lays her eggs, the male will guard them until they hatch, about eight days. At this point, he takes them into his mouth and they go into his vocal sac through a slit where they stay to develop. A male Darwin frog’s vocal sac is much more expanded than a normal frog’s and runs the length of his belly. It also produces special secretions that provide the young with nutrients. The only difference between species when it comes to the technique involved with this brooding method is time. The Chile Darwin’s frog male only keeps the tadpoles in his vocal sac for the first few stages of development, then takes them to a nearby stream or pool and releases them to mature fully. The Southern Darwin’s frog actually carries the tadpoles full term. These tadpoles may remain in his vocal sac for up to 50 days. When they are totally developed, he then regurgitates them as tiny froglets.
It is not yet known how or why this weird brooding behavior evolved and this is still a topic of research. One reason may be that it eliminates the dangerous period of time spent as a tadpole under the constant watch of predators. Most tadpoles of other frogs don’t survive to adulthood, but the Darwin’s frog tadpole receives the ultimate protection while in a male’s vocal sac. As strange a method as it may be, this form of reproduction has worked out well for these two species of Darwin’s frog and, with continued research and conservation, it will hopefully work for them for years to come.
References:
1. Bourke, J., et al. “Batrachochytrium dendrobatidis in Darwin’s frog Rhinoderma spp. in Chile.” Diseases of aquatic organisms 92.2 (2010): 217.
2. Soto-Azat, Claudio, et al. “The population decline and extinction of Darwin’s frogs.” (2013): e66957.
3. “Darwin’s Frog (Rhinoderma darwinii).” Arkive. Wildscreen Arkive, n.d. Web. 24 June 2015. <http://www.arkive.org/darwins-frog/rhinoderma-darwinii/>.
4. Alberto Veloso et al. Rhinoderma rufum. Red List. The IUCN Red List of Threatened Species, 2010. Web. 24 June 2015. < http://www.iucnredlist.org/details/19514/0>
5. Whittaker, Kellie and Chantasirisivisal, Peera. Rhinoderma rufum. AmphibeaWeb. 16 Feb. 2006. Web. 24 June 2015. < http://amphibiaweb.org/cgi-bin/amphib_query?where-genus=Rhinoderma&where-species=rufum>
Photo and Video Links:
1. https://flickr.com/photos/briangratwicke/
2. https://flickr.com/photos/chicuco/
