Data from: Love the one you're with: proximity determines paternity success in the barnacle Tetraclita rubescens

A species’ mating system sets limits on the strength of sexual selection. Sexual selection is widespread in dioecious species, but is less well documented in hermaphrodites, and may be less important. We used four highly polymorphic microsatellite markers to assign paternity to broods of the hermaphroditic eastern Pacific volcano barnacle Tetraclita rubescens. These data were used to describe the species’ mating system and to examine factors affecting male reproductive success. Tetraclita can sire broods over distances of 11.2 cm, but proximity to the sperm recipient had a highly significant effect on the probability of siring success. There was no effect of body size or the mass of male reproductive tissues on siring success. Broods showed relatively low frequencies of multiple paternity; even at high densities, 75% of broods had only one father. High frequencies of single-paternity broods imply either that this species does not compete via sperm displacement, or that sperm displacement is extremely effective, potentially explaining the lack of a positive relationship between male investment and paternity. In addition, there was low variance in siring success among individuals, suggesting a lack of strong sexual selection on male traits. Low variance among sires and the strong effect of proximity are likely driven by the unusual biology of a sessile copulating species.

物种的交配系统会限定性选择的作用强度。性选择在雌雄异体（dioecious）物种中普遍存在，但在雌雄同体（hermaphrodite）物种中的研究记载相对匮乏，且其作用可能较为有限。本研究采用4个高度多态的微卫星标记（microsatellite marker），对东太平洋雌雄同体火山藤壶红笠藤壶（Tetraclita rubescens）的育幼群开展父权鉴定。上述数据被用于解析该物种的交配系统，并探究影响雄性繁殖成功的相关因素。红笠藤壶可在11.2 cm的距离范围内成功繁育父本育幼群，但与精子接收个体的空间邻近程度对父权成功概率具有极显著影响。个体体型及雄性生殖组织重量均未对父权成功率产生显著影响。该物种的育幼群多父本现象频率相对较低；即便在高密度种群中，仍有75%的育幼群仅由单个父本产生。高比例的单父本育幼群暗示，该物种要么不通过精子置换展开繁殖竞争，要么精子置换机制极为高效——这或可解释为何雄性繁殖投入与父权成功率之间未呈现正相关关系。此外，不同个体间的父权成功方差较低，表明该物种的雄性性状未受到强烈的性选择作用。父本间的低方差以及空间距离的强影响效应，大概率由这类固着交配物种的特殊生物学特性所驱动。