Selection for costly sexual traits results in a vacant mating niche and male dimorphism

The expected strong directional selection for traits that increase a male's mating ability conflicts with the frequent observation that within species, males may show extreme variation in sexual traits. These male reproductive polymorphisms are usually attributed to direct male-male competition. It is currently unclear, however, how directional selection for sexually selected traits may convert into disruptive selection, and if female preference for elaborate traits may be an alternative mechanism driving the evolution of male polymorphism. Here we explore this mechanism using the polyandric dwarf spider Oedothorax gibbosus as a model. We first show that males characterized by conspicuous cephalic structures serving as a nuptial feeding device (‘gibbosus males’) significantly outperform other males in siring offspring of previously fertilized females. However, significant costs in terms of development time of gibbosus males open a mating niche for an alternative male type lacking expens...预期中针对提升雄性交配能力的性状所施加的强烈定向选择，与学界频繁观测到的同一物种内雄性性性状存在极端变异的现象相矛盾。这类雄性生殖多态性通常被归因于直接的雄性间竞争。然而目前尚不清楚，针对性选择性状的定向选择如何转化为歧化选择，以及雌性对精细复杂性状的偏好是否为驱动雄性多态性演化的另一潜在机制。本研究以多配侏儒蜘蛛Oedothorax gibbosus为模式物种，探究这一机制。我们首先证实，以显眼头部结构作为婚饲装置的雄性（下称‘驼背雄性’），在使此前已完成受精的雌性产下后代的成功率上显著优于其他雄性。然而，驼背雄性在发育时长上需付出显著代价，这为另一种缺乏昂贵发育成本的雄性类型开辟了交配生态位...