Sexual selection and proteinaceous diversity in the femoral gland secretions of lacertid lizards

Abstract. Sexual selection contributes to the diversity of chemical signals in various animal groups. Lizards are good model species to study how sexual selection shapes signal diversity, as they are a chemically oriented taxonomic group with different levels of social interactions. Many lizard species bear epidermal glands secreting waxy mixture of lipids and proteins which are used in intraspecific communication. Previous among-species comparative analyses failed to find a relationship between the strength of sexual selection on the composition of the lipid blend in lizards. Here we extend the investigation to the proteinaceous fraction. By using a phylogenetically informed approach, we correlated the average electrophoretic profiles of the protein from the femoral glands of 36 lacertid lizard species with the level of sexual dimorphism in size and shape, proxy for the strength of sexual selection. We found that as sexual size dimorphism advances, five distinct molecular weight regions in the protein profile increased their expression. Using tandem mass spectrometry, we successfully identified one of these five proteins: a carbonic anhydrase, an enzyme catalyzing the reversible hydration of carbon dioxide. Our findings suggest that proteins may be the target of sexual selection, as active semiochemicals or as dynamic support to other molecules: sexual selection may act indirectly on semiochemicals (namely lipids) by modifying the matrix (namely proteins).

SDS-PAGE.jpg Figure combining the sodium dodecyl sulphate-polyacrylamide gels of the femoral gland secretions of the lizard species we used to excise the bands for mass spectrometry (MS) analysis. The highlighted bands associate with a sexual size dimorphism increase. Top: gel of the four samples of Acanthodactylus scutellatus (each run twice to ensure having enough protein concentration for MS) used for bands A and B); bottom: gel of the two samples of Gallotia stehlini (each run twice) used for bands C, D, and E. A-E letter corresponds to the available raw MS files.

A.mzXL. Raw file of the spectra obtained by tandem MS in the open mzXL format for band A (see SDS-PAGE.jpg).

B.mzXL. Raw file of the spectra obtained by tandem MS in the open mzXL format for band B (see SDS-PAGE.jpg)

C.mzXL. Raw file of the spectra obtained by tandem MS in the open mzXL format for band C (see SDS-PAGE.jpg)

D.mzXL. Raw file of the spectra obtained by tandem MS in the open mzXL format for band D (see SDS-PAGE.jpg)

E.mzXL. Raw file of the spectra obtained by tandem MS in the open mzXL format for band E (see SDS-PAGE.jpg)