Variations in righting behaviour across Hermann's tortoise populations

Abstract

In terrestrial animals with rigid protective structures, the ability to upright after being overturned can make the difference between life and death, especially in suboptimal thermal conditions or in the presence of predators. This trait is assumed to be under strong selection. Different factors can influence righting ability, body dimensions and body mass for instance. As these morphological traits diverge among populations, inter-population variability in righting ability is expected. Previous studies on tortoises were performed within single populations and they usually focused on juveniles raised in captivity, precluding an assessment of the inter-population variability in a natural (realistic) context. In the current study, we quantified the righting performance in four populations of free-ranging adult tortoises. We found strong differences in righting success among populations and between genders, suggesting possible adaptations to local conditions. For instance, the topography (e.g. slopes) of each study site varied markedly. On average, males were more successful in righting themselves than females. Body size did not influence righting performances in males, but larger females were less successful compared to smaller ones. The success in righting was positively correlated with carapace domedness (height) and short bridges.