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The brain is inherently bisexual, differentiating during development so that in adulthood, males mount receptive females. Yet, vestiges of this bisexuality persist in adults, with heterotypical behaviors (females mounting and males being receptive) observed in some species. Consequently, differences in sexual behavior between the sexes, and between individuals of the same sex, are reflective of the predisposition and degree to which these behaviors are exhibited. How one behavior is facilitated and its complement simultaneously suppressed during a reproductive encounter suggests that behavioral expression is gated in some manner. Because male and female vertebrates typically display behavior characteristic of their own sex, simultaneous study of neural circuits gating homotypical and heterotypical behaviors in conventional animal models has received scant attention. The whiptail lizard species, Cnemidophorus uniparens, comprises individuals that are genetically and hormonally female, and that naturally display both types of behavior. Using High Pressure Liquid Chromatography (HPLC), immunocytochemistry, in situ hybridization, intracranial surgeries, as well as pharmacological and behavioral analyses, I report that serotonin levels, and signaling via distinct serotonergic receptors at behaviorally relevant brain nuclei might allow the system to switch between either behavioral repertoire. The use of the same molecule to mediate the reciprocal inhibition of complementary behavioral repertories within the same sex is evidence of a phenomenon of molecular parsimony underlying a striking form of behavioral plasticity. This dissertation also illustrates that sexually differentiated traits such as male and female-typical sexual behaviors are sculpted by neurochemical signaling at neural substrates present in both sexes. / text

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

I focus on phylogenetic relationships of teiid lizards beginning with generic and species relationship within the family, followed by a detailed biogeographical examination of the Caribbean genus Pholidoscelis, and end by studying species boundaries and phylogeographic patterns of the widespread Giant Ameiva Ameiva ameiva. Genomic data (488,656 bp of aligned nuclear DNA) recovered a well-supported phylogeny for Teiidae, showing monophyly for 18 genera including those recently described using morphology and smaller molecular datasets. All three methods of phylogenetic estimation (two species tree, one concatenation) recovered identical topologies except for some relationships within the subfamily Tupinambinae (i.e. position of Salvator and Dracaena) and species relationships within Pholidoscelis, but these were unsupported in all analyses. Phylogenetic reconstruction focused on Caribbean Pholidoscelis recovered novel relationships not reported in previous studies that were based on significantly smaller datasets. Using fossil data, I improve upon divergence time estimates and hypotheses for the biogeographic history of the genus. It is proposed that Pholidoscelis colonized the Caribbean islands through the Lesser Antilles based on biogeographic analysis, the directionality of ocean currents, and evidence that most Caribbean taxa originally colonized from South America. Genetic relationships among populations within the Ameiva ameiva species complex have been poorly understood as a result of its continental-scale distribution and an absence of molecular data for the group. Mitochondrial ND2 data for 357 samples from 233 localities show that A. ameiva may consist of up to six species, with pairwise genetic distances among these six groups ranging from 4.7–12.8%. An examination of morphological characters supports the molecular findings with prediction accuracy of the six clades reaching 72.5% using the seven most diagnostic predictors.