Progesterone induction of pseudocopulatory behavior and stimulus-response complementarity in an all-female lizard species.

Individuals of the all-female whiptail lizard species (Cnemidophorus) exhibit male-like and female-like pseudocopulatory behaviors that are correlated with stages of the ovarian cycle. Here we report on the hormonal bases of these behaviors. Parthenogenetic C. uniparens were ovariectomized and given Silastic implants containing either progesterone (P) or estradiol (E2); untreated controls received blank implants. Ten pairs of the following combinations were observed: P females paired with E2 females, P females paired with blank females, and E2 females paired with blank females. Each pair was observed at regular intervals 4 hr a day for 6 days. Pseudocopulations were observed between P and E2 animals; P animals consistently assumed the male-like role while E2 females assumed the female-like role. No pseudosexual behavior was observed between individuals of either P and blank or E2 and blank pairs. These data indicate that the postovulatory surge in P mediates male-like pseudosexual behaviors and the preovulatory surge in E2 mediates female-like pseudosexual behaviors in C. uniparens. Further, a complementarity in the behavior and physiology of both participants (male-typical mounting and female-typical receptivity) are important factors in pseudocopulatory behavior.