Removal of an evolutionarily-reduced color signal, and restoration of the signal to the ancestral state, influence male-male interactions in the striped plateu lizard, Sceloporus virgatus
Bulletin of the Maryland Herpetological Society 35(4): 115-142
Male Sceloporus lizards vary tremendously in the intensity and coverage of blue belly and throat coloration. In the striped plateau lizard, S. virgatus, the amount and intensity of blue coloration have been greatly reduced during evolutionary history to only two small, pale throat patches and, in some individuals, a few pale blue belly scales. I examined the influence of male coloration on male-male interactions and female choice in S. virgatus. Using paint to manipulate male color, I enhanced the amount and brightness of blue throat and belly coloration to restore the evolutionarily-reduced coloration to the ancestral state. In another experiment, I covered the naturally-occurring blue throat coloration. The presence or absence of blue coloration had no discernible effect on female choice, but I found an influence of coloration on male-male interactions. Resident males tended to win contests against intruders with restored levels of blue belly and throat coloration only when residents were larger than the intruders, suggesting a possible advantage of the restored color for larger intruders but not for smaller intruders. In the presence of a female, males with natural levels of blue coloration tended to exhibit social dominance over males lacking coloration and to lose less weight than males lacking normal levels of throat coloration. In S. virgatus the vestigial expression of the suspected sexual signal coexists with no apparent female response but a weak male response to the coloration.