Despite the established dichotomy between investment in either reproduction or self-maintenance, a hormonal mechanism that influences an organism's decision to prioritize these behaviors remains elusive. The protein hormone leptin is a likely candidate because it is secreted from adipocytes in proportion to the amount of stored fat in numerous species. Although the majority of studies suggest that leptin stimulates reproduction, the actions of leptin can be context-dependent. Leptin increases sexual behavior in fed individuals, but inhibits sexual behavior in food-restricted individuals. We investigated if exogenous leptin influences sexual behavior in red-sided garter snakes (Thamnophis sirtalis parietalis) experiencing a predictable bout of aphagia during the mating season. We tested two doses of recombinant murine leptin injected for three days. Males were subjected to three mating trials, one on each day of injections, while females were subjected to one mating trial on the last day of injections. Leptin affects male and female snakes similarly by increasing both appetitive (i.e., mating behavior score) and consummatory (i.e., number of copulations, proportion of individuals copulated) sex behavior. We found no evidence to suggest that leptin influenced latency to copulate or duration of copulation. Because leptin promotes reproductive behavior in non-feeding garter snakes, these findings do not align with research on food-restricted mammals. Further investigations into how leptin affects sexual behavior in snakes exposed to food-restriction manipulations would clarify if the role of leptin is evolutionarily divergent.

尽管在繁殖投资或自我维持投资之间已经确立了二分法，但影响生物体决定优先考虑这些行为的激素机制仍然难以捉摸。蛋白质激素瘦素是一个可能的候选者，因为它是由脂肪细胞分泌的，与许多物种中储存的脂肪量成比例。尽管大多数研究表明瘦素刺激生殖，但瘦素的作用可能取决于环境。瘦素增加进食个体的性行为，但抑制进食受限个体的性行为。我们调查了外源性瘦素是否会影响红边吊带蛇的性行为（Thamnophis sirtalis parietalis) 在交配季节经历可预见的吞食症。我们测试了注射三天的两剂重组鼠瘦素。雄性进行三次交配试验，每天注射一次，而雌性在注射的最后一天进行一次交配试验。瘦素通过增加食欲（即交配行为得分）和完美性（即交配次数、交配个体的比例）性行为来类似地影响雄性和雌性蛇。我们没有发现任何证据表明瘦素影响交配潜伏期或交配持续时间。由于瘦素促进不进食的吊袜带蛇的繁殖行为，因此这些发现与对食物受限哺乳动物的研究不一致。