I use reptiles as models for studying ecological speciation. To this point, much of my work on this topic has focused on color evolution in Chihuahuan Desert lizards. Three lizard species exhibit striking variation in coloration associated with geologically recent formations in the Chihuahuan Desert. Blanched color morphs of the Little Striped Whiptail (Aspidoscelis inornata), the Lesser Earless Lizard (Holbrookia maculata) and the Eastern Fence Lizard (Sceloporus undulatus) inhabit the white gypsum dunes of White Sands, a melanic color morph of S. undulatus is found on the black basalt rocks of the Carrizozo Lava Flow, and brown color morphs of all three species are associated with the surrounding desert soils. Substrate matching for these small diurnal lizards is critical for avoiding visual predators. The phenotypic variation along this gradient of black to white provides complementary natural “experiments” which have occurred in the last 2,000-6,000 years. Some of my specific research foci in this system include:

The demography of local adaptation: Using multi-species and multi-habitat comparisons, I endeavor to understand how population demography can influence organismal response to natural selection and how, in turn, demographic histories can be shaped by natural selection. For example, I compare multiple species exposed to the same environmental gradient at White Sands and ask how species-specific attributes (e.g., dispersal capability, life history strategy) may affect phenotypic response to selection. I also compare populations of single species, that are continuously distributed across the white sand, dark soil and black lava habitats to ask whether there are predictable demographic signatures associated with the colonization of novel habitats.

The genetic basis of coloration: To develop a more mechanistic understanding of how organisms adapt to changing environments, I have been studying the genetic basis of reptile color variation. Much of this work has focused on the melanocortin-1 receptor gene (Mc1r) because of its key role in the pathway that produces melanin in vertebrates. Comparing results from candidate gene studies in multiple reptiles allows me to better understand whether changes at the same genes underlie similar adaptations in different species.

The interaction between natural and sexual selection: The potential for natural selection across environmental gradients to lead to reproductive isolation is often mediated by coincident evolution of ecological divergence and mating preference. I evaluate the potential for interaction of natural and sexual selection in this system by conducting field based mate-choice experiments and by studying color patches which lizards may use for intraspecific communication rather than crypsis.