“Laurel and Hardy effect” spells good news for captive breeding

Animals bred in captivity for reintroduction to the wild are able to retain their defences against predators for several generations, ecologists have found. According to new research published in the British Ecological Society’s Journal of Applied Ecology, tadpoles of the Mallorcan midwife toad (Alytes muletensis) retain their ability to change their body shape – a defence they have evolved in the face of predators – even after being bred in captivity for three to eight generations. The results have important implications for conserving endangered species through captive breeding programmes.

Tadpoles of many amphibians have developed ways of defending themselves against predators. Mallorcan midwife toad tadpoles grow longer tails and shallower fins to help them escape from danger when predators are present. These defences have evolved in response to two predators that were introduced to Mallorca about 2,000 years ago: the viperine snake (Natrix maura) and the green frog (Rana perezi). The authors of the paper, Dr Richard Griffiths and colleagues from the University of Kent and the University of Sussex, have dubbed this change in shape the “Laurel and Hardy effect”.

The researchers compared the responses of tadpoles in a predator-free, reintroduced population with those in the population from which their ancestors were collected several years earlier. When the tadpoles were exposed to chemical cues from predators, the researchers found that the reintroduced population retained their anti-predator responses, even though they had been bred in captivity for three to eight generations in the absence of predator selection pressures.

They also compared how tadpoles bred in captivity for differing lengths of time responded to chemical cues from these two predators, and found that after nine to 12 generations, the tadpoles began to lose their ability to change shape in response to predators.

According to the authors: “It is reassuring that reintroduced populations can retain important anti-predator responses in the absence of selection for several generations. Nevertheless, long-term captive breeding reduced both adaptive and neutral variation in this species.”

The results have important implications for captive breeding programmes. “There aren’t many conservation options for halting global amphibian declines, but captive breeding is one of them. We now know that it is possible to breed endangered species in captivity for several generations without compromising important fitness attributes,” the authors say.