Social behavior, chemical communication, and adult neurogenesis: studies of scent mark function in Podarcis wall lizards.

Lacertid lizards have been hailed as a model system for the study of reptilian chemical communication. However, results obtained with the genus Podarcis, a diverse group of wall lizards with complex systematics, challenge emerging paradigms and caution against hasty generalizations. Here we review the available evidence on the role of chemical stimuli in male-female and male-male interactions in Iberian Podarcis. Males of several species can discriminate between chemicals left on substrates by females of their own or a different species, suggesting that differences in female chemical cues may underlie species recognition in this group. Females, on the other hand, do not respond differentially to conspecific and congeneric male scent marks. Males of Podarcis liolepis use scent marks to recognize rivals individually, evaluate their competitive ability (i.e., body size), and assess the threat posed by each individual rival neighbor. In contrast, females do not exhibit a preference for territories scent marked by larger (i.e., more competitive) males, which suggests a limited role for male scent marks in pre-copulatory mate choice. This behavioral sex difference is consistent with detailed neuro-ethological evidence showing that chemosensory brain areas in P. liolepis are sexually dimorphic. The accessory olfactory bulbs are larger (both in absolute and relative terms) in males than in females, probably as a result of sex-specific rates of adult neurogenesis. In both sexes, cell proliferation undergoes seasonal cycles that may have evolved to satisfy increased chemosensory demands at particular times of the year. Overall, and against recent generalizations, these results suggest that male scent marks have been shaped mainly by strong intrasexual selection.