Links between male quality, male chemical signals, and female mate choice in Iberian Rock Lizards

1. In spite of the fact that chemoreception plays an important part in sexual selection of many vertebrates, there is a lack of general knowledge on the role of specific chemical compounds as sexual signals, and on how the characteristics of chemical signals mediate behaviours such as mate choice. 2. We examined how female Iberian Rock Lizards use the chemical characteristics of femoral gland secretions of males to select potential mates. 3. Tongue-flick assays and choice of scent trials showed that females discriminated by chemosensory cues alone differences in chemical secretions of different males. Females showed stronger chemosensory responses and preferred the scent of males of presumably high quality (i.e. those more symmetric and with a greater immune response). 4. Chemical analyses by gas chromatography-mass spectrometry showed that these preferred males allocated relatively more cholesta-5,7-dien-3-ol and ergosterol to femoral secretions, which suggested that females used these chemicals to choose between males' scents. 5. Further experiments confirmed that females were able to discriminate cholesta-5,7-dien-3-ol, ergosterol, and changes in their concentrations, from similar steroids (i.e. cholesterol) also found in secretions of males. Moreover, females were more attracted to areas that were experimentally manipulated to increase the proportion of ergosterol in natural scent marks of males. 6. We suggest that femoral secretions with higher proportions of cholesta-5,7-dien-3-ol and ergosterol might be reliable advertisements of quality of a male, which females could use to select mates.