Differential effects of testosterone and progesterone on the activation and retention of courtship behavior in sexual and parthenogenetic whiptail lizards
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Abstract
Both testosterone (T) and progesterone (P) facilitate the expression of male-typical
sexual behavior in a variety of animals, including rodents and lizards. In two species
of whiptail lizards, Cnemidophorus inornatus and C. uniparens, both hormones elicit
the full repertoire of courtship behavior. However, the relative efficacy of the two
hormones is unknown. In Experiments 1 and 2 we assessed differences in capacity of
exogenous T and P to induce male-typical courtship behavior in gonadectomized whiptail
lizards. In both species, individuals implanted with T showed more frequent courtship
behavior relative to those implanted with P or cholesterol. In Experiments 3 and 4
we examined whether T and P differentially affected the retention of courtship behavior
following implant removal. In both species, individuals implanted with T showed more
courtship behavior following implant removal than those previously given P. In these
experiments, implants were removed at a time when individuals in both groups were
behaviorally similar; therefore, the differences in behavior following implant removal
were not due to differences in the amount of courtship experience. Taken together,
the hormone that was more effective at activating courtship behavior was also more
effective at maintaining courtship behavior following implant removal. In summary,
though both T and P can elicit identical sexual behaviors in both whiptail species,
T has a greater and more lasting effect on courtship behavior and possibly on the
neural circuits underlying courtship behavior.