Too mellow for our predatory world

Marine iguanas on the Galápagos Islands live without predators - at least this was the case up until 150 years ago. Since then they have been confronted with cats and dogs on some islands of the Archipelago. For scientists, they are therefore a suitable model of study in order to discover if such generally tame animals are capable of adapting their behaviour and endocrine stress response to novel predation threats. Scientists from the Max Planck Institute for Ornithology, the University of Ulm Tufts University and Princeton University were able to show that the stress response induced by corticosterone (CORT) is absent in predator-naïve animals but can be fully restored with experience. However, as the researchers found out, the flight distance of the reptiles does not sufficiently increase, which limits their ability to successfully escape from newly introduced predators (Proceedings of the Royal Society, FirstCite Early Online Publishing December 2006).

Who of us has not dreamt of living on an island" Apparently, island life has certain advantages. This is also true for the marine iguanas. For millions of years they have lived without natural predators. In the course of evolution they have become excessively tame. Hundreds of reptiles doze, spread-eagled, on black lava rocks, soaking up the sun - behaviour that would be unthinkable in an environment with predators, where reptiles are persistently exposed to the threat of being devoured by others.

The absence of predators may lead to adaptations in the behaviour of insular animals. Over a longer evolutionary period, birds for example can lose their ability to fly. This would greatly reduce their ability to escape should new predators appear. In contrast to such "hard wired" traits, however, behavioural patterns should be significantly more flexible. In programmes introducing tame species into the wild, animals are trained to recognise and cope with predators. But in most cases it is very diffic

Contact: Dr. Thomas Roedl

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