Differences in males’ chemical signals between genetic lineages of the lizard Psammodromus algirus promote male intrasexual recognition and aggression but not female mate preferences

Interpopulational variation in sexual signals may lead to premating reproductive isolation and eventually may result in speciation. We explored the role of chemical cues secreted by the femoral glands of male lizards Psammdoromus algirus in chemosensory recognition between two distinct genetic lineages from Central Spain. We hypothesized that if there were differences in chemical sexual signals between lineages, these may result in differential recognition and mate preferences. This might lead to reproductive isolation, which would allow the observed morphological and genetic differences between lineages. Our results showed that males of each lineage secreted a singular mixture of compounds in their femoral secretions. However, females were apparently not able to discriminate the lineage of males by chemosensory cues or, alternatively, this discrimination may not be important for females. Moreover, females did not select or reject areas scent marked by males of their own vs. the other lineage. However, previous studies suggest that females might prefer scent of males with particular chemical characteristics that show interindividual variability but do not vary between lineages. Similarly, males did not discriminate between the scents of females of the two lineages, although they had greater chemosensory responses to scents of larger females. In contrast, males clearly discriminated the lineage of other males based on their scents alone, showing chemosensory and aggressive responses that were higher to scents of males of the other lineage. If males of the opposite lineage were more prone to be detected and excluded from a male territory due to their differences in chemical signals, this may probably impede the access of males of one lineage to females of the opposite lineage. This might result in reproductive isolation between lineages. We suggest that the current genetic divergence observed between lineages of P. algirus lizards may be mediated by intrasexual relationships among males, but not by female mate preferences. Significance statement Sexual signals often vary geographically to maximize their efficiency in communication under local conditions. Such variation may, however, affect recognition between individuals of different populations, resulting in reproductive isolation and speciation. We studied two populations (lineages) of a lizard with genetic and morphological differences. We found clear inter-lineage variation in chemical profiles of sexual signals of males. However, females did not recognize these differences by chemosensory cues and did not prefer or reject areas scent-marked by males of the two lineages. In contrast, males recognized and responded more aggressively toward scent of males of the opposite lineage. This might impede access of males of one lineage to females of the other. We suggest that the observed differences between lineages may result from partial reproductive isolation, which can be mediated by agonistic interactions between males rather than by female mate preferences.