Postcopulatory sexual selection as a driver of sex- and population-specific kidney mass in garter snakes?

In lizards and snakes, the kidneys produce seminal fluid in addition to having osmoregulatory functions. Therefore, in response to polyandry, kidney mass should be under selection regimes like those influencing testes. Male red-sided garter snakes deposit a kidney-derived copulatory plug that functions in sperm competition. We first tested for intersexual differences in kidney mass and allometry in one population and found that males had kidneys twice as heavy as those of females, consistent with stronger selection on male kidney mass. Previous studies have shown that male size enhances mating success in one-on-one competition prevalent in small mating aggregations. We then examined the relationship between body size, kidney mass, and testes mass in two populations with low (LD) and high (HD) mating aggregation densities. Males from the HD population had heavier testes and heavier kidneys than did males from the LD population; HD males were also smaller in body size. Our results suggest...在蜥蜴与蛇类中，肾脏除具备渗透压调节（osmoregulatory）功能外，还可产生精液（seminal fluid）。因此，针对一妻多夫制（polyandry）现象，肾脏质量应当处于与影响睾丸的选择模式相似的选择压力之下。雄性红边束带蛇会分泌一种源自肾脏的交配栓（copulatory plug），该结构在精子竞争（sperm competition）中发挥功能。我们首先在一个种群中检测了肾脏质量与异速生长（allometry）的两性差异，结果发现雄性肾脏质量为雌性的两倍，这与雄性肾脏质量承受更强选择压力的结论相符。既往研究表明，在小型交配聚集群中普遍存在的一对一竞争场景下，雄性体型越大，交配成功率越高。随后，我们在交配聚集密度较低（LD）与较高（HD）的两个种群中，探究了体型、肾脏质量与睾丸质量之间的关联。结果显示，来自高密度（HD）种群的雄性，其睾丸与肾脏质量均高于低密度（LD）种群的雄性；同时高密度种群的雄性体型更小。我们的研究结果表明……