Evolution of neuroendocrine mechanisms that regulate sexual behavior.

Whiptail lizards provide a unique system to study evolution of brain mechanisms because both ancestral (sexual) and descendant (parthenogenetic) species exist. Parthenogenetic whiptails enable us to avoid the two major confounds in sex differences research - males and females that differ both genetically and hormonally. Parthenogens are females that reproduce clonally, yet display alternately female-like and male-like pseudosexual behavior. Thus, the neural circuitry underlying male and female sexual behavior can be examined within the 'same' brain (same genome), enabling us to see how neuroendocrine mechanisms controlling mounting behavior change. In ancestral males, testicular androgens control sexual behavior, whereas male-like pseudocopulatory behavior is controlled by ovarian progesterone in parthenogens, revealing that progesterone is important in regulating sexual behavior in male vertebrates, including mammals.