Record Details

Bissell, Ahrash N.
Population differences and behavior of lizards: on the road to speciation?
Cyclura carinata
In order to understand the importance of the enormous biological diversity that exists today, we need to know how diversity is generated via speciation. One possibility is that separate populations within a species can evolve differences in morphology, behavior and/or genetics which eventually reduce or eliminate inter-population mating events, generating new species. In this dissertation, I focused on the causes and consequences of behavioral differentiation as a potential isolating mechanism among populations of two different lizard species, Cyclura carinata and Sceloporus eraciosus. Looking at the rock iguana, Cyclura carinata in the Turks and Caicos Islands, I found that different island populations showed significant variation in display behavior, and that these differences were correlated with island habitat differences. Based on these results, it was clear that these lizards could evolve population-specific behavioral differences very quickly. Next, I looked at combinations of morphologically-manipulated images and live lizards to contrast the motivation and direction of preferences between two populations of the sagebrush lizard, Sceloporus graciosus. I found that the populations were significantly different in their motivation and responses to the different types of stimuli: males from one population responded mostly to behavioral traits whereas the other population exhibited no such motivational differences. Communicative behavior in S. graciosus includes the use of both visual displays and chemical pheromonal secretions; therefore, I ran a series of experiments where I exposed male lizards to different combinations of visual and chemical stimuli. I found that the lizards responded more strongly to the treatment with both stimuli, showing that the different types of signals interact to modulate (or change) the response behavior accordingly. Finally, I ran a series of experiments in which I tested for population discrimination in S. graciosus. I found that males showed a preference for females from their own population. This final experiment demonstrated that lizards can tell different populations apart, suggesting that the vast behavioral and morphological differentiation that exists in the natural world might be illustrative of the continuous process of populations diverging and eventually leading to new species.