UC Santa Cruz

Discrete variation in colorful sexual signals is often associated with variation in reproductive tactics or strategies. Many taxa with intrapopulation color polymorphisms also exhibit variation among populations or among closely related species in the frequency of color morphs, the number of morphs present within a population, or which particular colors are used as signals. These patterns may be important for understanding speciation because theoretical and empirical studies indicate that both color polymorphism and alternative reproductive tactics may be associated with elevated diversification rates. I studied variation in throat color, an important sexual signal, within and among populations of the mesquite lizard (Sceloporus grammicus) species complex. The S. grammicus species complex is considered a possible example of incipient speciation due to high levels of variation in chromosome number, habitat use, reproductive cycles, and life history. My first chapter confirms this variability in female life history, and the rest of my dissertation is the first research to address sexual signals in S. grammicus. I performed a broad geographic survey of throat color polymorphisms and used laboratory behavioral trials and molecular phylogenetics to investigate the meaning and evolutionary context of the polymorphisms I observed. I found that male S. grammicus within a single population exhibited either orange, yellow, and blue throat color morphs or orange, yellow, and white throat color morphs. In no case did I observe the blue male morph and the white male morph in the same population. I found that both the orange/yellow/blue and orange/yellow/white polymorphisms in males were associated with variation in male aggression level, but the meanings of particular colors were different between the two populations I studied.

I also found that females performed more rejection behaviors towards allopatric males when those males were of a color morph that did not occur in the female's home population than when the allopatric male was of a color morph that did occur in the female's home population. Finally, I constructed a phylogeny of the populations I had sampled and used ancestral state reconstruction to establish that the white male morph in the S. grammicus complex has originated at least twice.