Lateralized righting behavior in the tortoise ( Testudo hermanni)

Abstract

Lateralization of brain and behaviour at the population level has been documented in all vertebrate classes. Research was mostly carried out on mammalian and avian species, the least investigated class with this regards being the Reptilia, with studies concentrating on lateralized aggressive behaviour in lizards. No research has been carried out on lateralization in the Chelonian order. We investigated the presence of motor asymmetries in the tortoise Testudo hermanni, using the righting response (i.e. the animal is positioned upside-down and the left/right side to which it uprights is observed), a procedure already employed to assess behavioural lateralization in amphibians. The ability of righting has a particularly high adaptive value in tortoises, as in case of overturning, and consequent exposure to sunrays, changes in body temperature and difficulties in respiration could occur leading to serious conditions. Thirty-four tortoises underwent a series of righting tests in a standardized apparatus, 15 tortoises were also retested 10 months later. A bias at the individual as well as at the population level was found for preferentially turning on the right side. Consistency of responses at retest was also observed. The results are discussed with reference to the implications for the evolution of brain lateralization in vertebrates.