Body Size Evolution

For my dissertation research, I investigated dwarfed populations of short-horned lizards (Phrynosoma hernandesi) and Great Plains toads (Anaxyrus cognatus) in the San Luis Valley (Valley), Colorado.Although there is clinal variation in body size over latitude and elevation, horned lizards and toads in the 8,000mi² Valley show an abrupt and disjunct reduction in body size, and are over 30% smaller than populations outside the Valley. Valley populations are morphologically unique in their body proportions (dwarfed) and show an increase in sexual size dimorphism, which is contrary to principles of allometric scaling. Phylogenetic analyses suggest that Valley populations are historically and currently isolated within the Valley. Their biogeographic histories include radiation from the southern end of the Valley and current population sub-structuring that corresponds with the 5 physiographic provinces in the Valley. Additionally, molecular data suggest that Valley populations represent unique lineages that should be considered for taxonomic revision.

Currently, I am working with two undergraduate research students to determine the effects of latitude on body morphology. We are investigating morphological shifts of desert horned lizards (Phrynosmoa platyrhinos) and desert spiny lizards (Sceloporus magister) in two desert environments, one cold (Sagebrush desert, northern Nevada) and one hot (Mohave desert, southern Nevada).