Discrimination of conspecifics’ chemicals may allow Spanish terrapins to find better partners and avoid competitors

Chemosensory discrimination of sex and other individual traits based on pheromones occurs in many reptiles. However, the use of chemoreception in turtle social behaviour is poorly known. We examined the role of chemical signals in intraspecific communication of Spanish terrapins, Mauremys leprosa, during the breeding season. Chemical cues released by terrapins in the water might inform on sex and other individual characteristics, such as size, body condition or health state, which are important in sexual selection processes. To test this hypothesis, we compared the time spent by turtles in water pools containing chemical stimuli obtained from different conspecifics. Behavioural responses showed that turtles were able to detect and discriminate chemical cues released by conspecifics, and to modify their use of space in response to these cues alone. Males preferred water pools with chemicals of females with greater immune responses, while females preferred water pools with odours of larger males. Preferences for water used by better potential partners could increase mating opportunities with these partners, which would increase offspring fitness. Female preference for large males could also be a mechanism of protection from harassment by small males. On the other hand, males avoided water pools with chemicals of heavier, or relatively heavier, males and preferred water with chemicals of smaller, or relatively smaller, males. Chemosensory assessment of body size may allow males to minimize the risk of costly aggressive interactions with other males. Selection of water pools based on chemical cues of conspecifics may allow terrapins to optimize their mate searching while avoiding competitors.