Meeting Abstract
The endocrine mechanisms that mediate to what extent an individual invests in reproduction are poorly understood. Because reproduction is an energetically expensive activity, a hormone indicating accurate energy stores is a likely candidate for regulating reproductive investment. In numerous mammalian species, leptin accurately indicates fatty acid stores and influences reproductive hormones and behavior. To determine if the role of leptin is conserved across taxa, we injected red-sided garter snakes (Thamnophis sirtalis parietalis) with recombinant mouse leptin and measured reproductive behavior. We injected females with 0, 7, or 70 μg of leptin once a day for three days. Because female snakes become unattractive upon mating, females were subjected to a single mating trial. Male snakes were injected with 0, 3, or 30 μg of leptin once a day for three days and then subjected to a mating trial each day. We scored female and male mating behavior using ethograms. Although exogenous leptin did not affect female receptivity score, it significantly increased the proportion of females that copulated. Of the females that copulated, leptin did not affect latency to copulate or the duration of copulation. In male snakes, we found that leptin increased both courtship score and the number of copulations a male performed. Leptin did not influence latency to copulate, duration of copulation, the order of mating, or copulatory plug mass in males. In summary, the effects of leptin may be sexually dimorphic: exogenous leptin increased consummatory reproductive behavior in females, whereas it increased both appetitive and consummatory reproductive behavior in males. These data implicate leptin as a possible hormonal mechanism regulating individual variation in reproductive investment.
