Friday, August 19, 2011

Cane Toad Tadpole Cannibalism

Rhinella marina. JCM
Most tadpoles eat almost anything, they filter the substrate and water for organic mater taking in bacteria, decomposing matter, mud, and other kinds of molecules they can get energy from. The Marine Toad or Cane Toad as the Australians call them have tadpoles that have very flexible diets. A forthcoming article in Animal Behaviour reports Rhinella marina tadpoles will eat the eggs of their own species. The BBC is reporting on this article, and the original article can be found here.

Cane toad tadpoles cannibalise eggs to survive, and the behavior starts when they are just a few days old.It is a habit that reduces competition and provides the cannibals a nutritional boost.

"Toad tadpoles almost never encounter eggs that are closely related to them - so they can happily go ahead and munch any they find” says Professor Richard Shine, University of Sydney. Researchers from the University of Sydney and James Cook University, Queensland in Australia, wanted to find out why cane toad tadpoles ate the eggs of their own species.

Their study compared two groups of tadpoles, one group was allowed to eat toad eggs and the other was prevented.

The team found that cannibal tadpoles survived, grew and metamorphosed into toads more successfully than the tadpoles that did not eat the eggs.

Although the tadpoles benefited from the nutrition of the eggs, they also improved their chances for the future, according to Professor Richard Shine who lead the research.

"The most important benefit is not nutrition, but the reduction of competition from the tadpoles that otherwise would have hatched from those eggs," he said.

But the tadpoles' voracious appetites do not extend to their siblings, as Prof Shine explained.

"The tadpoles don't eat close kin eggs, because of the short incubation period and the long delay between successive clutches by a single female," he told BBC Nature.

"Thus, toad tadpoles almost never encounter eggs that are closely related to them - so they can happily go ahead and munch any they find, without the risk that they are eating their relatives."

Proffesor Shine's results build on his previous findings that cane toad tadpoles can detect eggs in a pond using their sense of smell.

"Toad tadpoles can use specific chemicals produced by toad eggs to locate those eggs and eat them," he explained.

"We were astonished to discover that these simple little creatures, with brains the size of a pinhead, can react in subtle ways to specific cues.

"The tadpoles have a secret chemical language that only they can detect and respond to."

Cane toads are native to South America but were introduced to Australia in 1935 to control sugar cane pests.

Original Article
Michael R. Crossland, Mark N. Hearnden, Ligia Pizzatto, Ross A. Alford and Richard Shine. 2011.Why be a cannibal? The benefits to cane toad, Rhinella marina [=Bufo marinus], tadpoles of consuming conspecific eggs. nimal Behaviour, In Press, Corrected Proof, Available online 9 August 2011.

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