Successful righting response in the Mediterranean Spur-thighed Tortoise, Testudo graeca terrestris Forskål, 1775, occurs only during the mating season and primarily by sexually motivated mature males

Increased activity during breeding season may increase the risk of overturning in male turtles. Righting response (the return to a dorsal-ventral position after being overturned) is considered to be a general index of physical fitness that influences survival and reproduction. We studied righting performance and success in the Mediterranean Spur-thighed Tortoise, Testudo graeca terrestris Forskål, 1775, in both sexes of different age groups and in different seasons by measuring the number of movement components of righting response behaviour: fore- and hind limb swings, head movements and turns, events of intensive and synchronized movements of all limbs and head, and side preference for the righting. We also took morphometric measurements of the posterior and anterior shell aperture widths and hind limb lengths to examine whether they could explain sexual differences in behaviour. Adult male T. g. terrestris had significantly higher righting success and limb movement compared to females, but only during the mating season. These differences were not found in juveniles (5.5 years old) or hatchlings (9 months old). Hind limbs were found to swing more rapidly than forelimbs in adult males compared to females in both seasons. We did not find a side preference for righting response behaviour. We further found that the ratio between the widths of posterior and anterior apertures was significantly larger in adult males than adult females. Juveniles did not display these sexual differences. The seasonally dependent increase we observed in the overall performance of T. g. terrestris males in righting response may have been selected to evolve because of the advantage it confers to males in the context of mate-searching. The behavioural sexual differences could not be explained only by sexual dimorphism, as they occur only during the mating season. Further research will be needed to discern if sexual differences in seasonal hormonal levels may contribute to the display of this behaviour.