A major question in evolutionary biology concerns the manner with which sexual selection pressures, such as mate choice and intrasexual competition, result in the origination and maintenance of elaborate ornamental traits. The selective forces influencing the evolution of female ornaments have been relatively ignored even though the occurrence of such traits is not as uncommon as traditionally assumed. Among lizards, for example, females of over 30 species express bright coloration that is absent in conspecific males.
My students and I examine the function and regulation of female ornaments, focusing on the striped plateau lizard (Sceloporus virgatus). Female striped plateau lizards develop orange color on their throats during the reproductive season. My working hypothesis is that males invest more resources into the courtship of more-ornamented females because these females are of higher quality and thus produce higher quality offspring. Females are expected to benefit from “indirect mate choice” – attracting males to them, inciting competition, and mating with higher quality winners, all while remaining sedentary during the energetically expensive period of egg development. To address this hypothesis, some of my research questions have included:
- How does the female ornament affect male behavior?
- Is the female ornament an honest signal of female phenotypic quality?
- Can the female ornament be used to predict characteristics of her offspring?
- What mechanisms (genetic or nongenetic) underlie the positive relationship between maternal ornamentation and offspring quality?
- How is female ornament expression regulated?
My students and I have recently expanded our work on female signals to include chemical signals. We have characterized the chemical make-up of female skin lipids cues, related individual variation in chemical cue composition to aspects of female reproductive state and condition, and examined male response to female cues (both whole cues and chemical standards of specific cue components).
In the long run, we want to address many of the same 5 questions bulleted above. In addition, we are examining whether the visual and chemical signals are redundant (i.e., provide the same information) or are instead providing distinct information to receivers.