Tadpoles and an Invasive Crustacean

After 30 years, the common frog can not activate their defenses against the American crayfish.

Iván Gómez Mestre and Carmen Díaz Paniagua, biologists from the Biodiversity Research Unit of the Principality of Asturias CSIC-Universidad de Oviedo and Station Biological relevance of Doñana (CSIC) respectively have confronted two groups of tadpoles with the American crayfish and have compared the degree of activation of their defenses. The researchers note that, despite the common frog tadpoles activated when they detect predators, are unable to perceive the American crayfish, which leaves no recourse for this invasive species.

"The common frog in the Doñana National Park has not yet adapted to the American red crayfish (Procambarus clarkii ) [photo]," said Iván Gómez Mestre. Both the common frog tadpoles in the wetlands of Donana, a town three decades has been in contact with this predator (between 10 and 15 generations), and tadpoles from populations that are faced by first time crab responded the same way: "The degree of activation of defenses is the same in both cases: null," says the biologist.

Tadpoles, explains, they have many defenses available to it, but when they detect the chemical signals (the smell dissolved in water) of a predator such as dragonfly larvae can morphological and behavioral changes.
"The changes in shape result in a wider tail and more pigmented, which attracts the predator to her leaving intact the vital organs and no tears or loss of tail have such serious consequences, since they can regenerate. And changes in behavior resulting in a reduction of activity that passed over unnoticed, "said Iván Gómez Mestre.

But these changes, despite improved survival in case of predators, have a price: "By reducing its activity, the tadpoles were fed less, grew more slowly and faced with the progress of your pond dry season, addition to give advantage to competitors for food, "says the researcher. Hence, the activation of defenses is not permanent and depend on the detection of the predator species by the tadpoles.
An evolutionary race

The results published today contribute to better understand the series of changes that occur in the Iberian ecosystems that invasive crab, native to the Southeastern U.S. and present from Doñana to Asturias. As indicated by Iván Gómez Mestre, among other effects "are known to be in areas that present the American crayfish is a proliferation of predatory birds, so that the pressure on amphibians increases even more."
"The question is whether common frog populations exposed to American crayfish have enough time before dying to adapt to the presence of an introduced predator so voracious. Can not venture a period in evolutionary terms, because each species responds differently, but a reference can be detected cases in the U.S. adaptation of bullfrog tadpoles by introduced fish against the man after 110 years of contact, "says researcher.

The species was detected 15 years ago in Asturian rivers. The American crayfish damage native ecosystems and particularly harmful to salmonids, small fish, amphibians, and vegetation waters. It has also displaced the native crayfish ( Austropotamobius pallipes lusitanicus) in almost all waterways.

This situation has led to initiatives such as the Crab Project: http://elbanzao-proyectocangrejo.blogspot.com/

Ivan Gomez-Mestre and Carmen Díaz-Paniagua. (2011)  Invasive predatory crayfish do not trigger inducible defences in tadpoles Proc. R. Soc. B published online 30 March 2011doi:10.1098/rspb.2010.2762

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