Evolutionary changes in dopaminergic modulation of courtship behavior in Cnemidophorus whiptail lizards

Preoptic dopamine release is integral to the display of copulatory behavior s in male mammals and birds. However, while the anatomical distributions of the dopamine synthesizing enzyme tyrosine hydroxylase are similar among ve rtebrates, evolutionary changes in the functional role of dopamine are poor ly understood. In this study, we tested whether a dopamine D1 receptor agon ist would facilitate the display of courtship and copulatory behaviors in t wo related Cnemidophorine lizards (Cnemidophorus inornatus and Cnemidophoru s uniparens). Cnemidophorus lizards offer a unique system to study evolutio nary changes in functionality because ancestral (e.g., C. inornatus) and de scendant (e.g., C. uniparens) species can be studied in parallel. Cnemidoph orus uniparens is an all-female, parthenogenetic species and is the triploi d descendant of the sexual and diploid species C. inornatus. Here we report that in castrated male C. inornatus and ovariectomized C. uniparens a dopa mine D1 agonist increased the proportion of individuals mounting and decrea sed the latency to mount. Moreover, there was a species difference in sensi tivity to the agonist: Mounting was elicited at a lower dose in C. uniparen s than in C. inornatus, One possible explanation for this heightened sensit ivity in the triploid parthenogen is that, by virtue of the increased ploid y, the parthenogen has elevated levels of DI receptor in limbic brain areas modulating courtship behavior. (C) 2001 Elsevier Science.