A comparison among sexual signals in courtship of European tortoises

Complex and ritualized displays require an assemblage of structural, neuronal, and muscular adaptations, whereas the habitat structure may highly affect the effectiveness of signals to convey information. Therefore, ornament exaggeration through sexual selection may be severely constrained by the costs imposed by natural selection. We investigated this compromise in the courtship behavior of the Mediterranean tortoises by assessing the variability of the acoustic and behavioral signals used in courtship among species, and the relationship between courtship and species body size. Marginated, Greek and Hermann’s tortoises base their courtship on the same kind of displays, and the difference among species relies mainly on the relative importance of aggressive displays respect to acoustic signals. In addition, we found that the divergence of courtship patterns among species was related to their body sizes. Greek tortoises, intermediate in size between the other two species, showed an intermediate courtship aggression. Body size in Mediterranean tortoises relates to different vegetation structure of their preferred habitat, smaller species being advantaged in denser vegetation. Therefore, the divergence of courtship patterns in the three species of European tortoises might have been promoted by the progressive adaptation of incipient species to habitats with different vegetation structures. Since courtship signals play a central role in species isolation, a linkage between morphology and courtship is of particular interest and might be one of the central mechanisms of tortoise diversification.