Differences in chemical signals may explain species recognition between an island lizard, Podarcis atrata, and related mainland lizards, P. hispanica

Abstract

Chemical signals can be the basis of interspecific recognition and speciation in many animals. The Columbretes Islands wall lizard, Podarcis atrata is very close genetically to the mainland Iberian wall lizard Podarcis hispanica. However, a previous study suggested that chemosensory interspecific recognition would avoid reproductive interactions and hybridization between these two species. These results suggested that chemicals used in intraspecific communication might differ in composition and/or proportions between these two species. In this paper, we used gas chromatography–mass spectrometry (GC–MS) to characterize the chemical composition of the lipophilic fraction from femoral gland secretions of male P. atrata and P. hispanica. The analysis showed that chemicals found in femoral secretions varied in composition and proportions between species and between populations. Seven steroids and two unidentified waxy esters, were exclusive of P. atrata lizards from the islands. In contrast, nine steroids and other six compounds were only found in mainland P. hispanica. There were also differences in proportions of shared compounds between species. Moreover, all these differences were higher between P. atrata and P. hispanica than between any population of P. hispanica. Chemical differences might be consequence of genetic differences, but they could also be explained by adaptation to different habitats with different climatic conditions or diet resources. Compounds that are specific of each species, or differences in the pattern of compounds, could explain species recognition. Therefore, these results of chemical composition and previous studies of chemosensory recognition reinforce the fact that the genetic differences between P. hispanica and P. atrata may result in an effective reproductive isolation between these two taxa.