Data from: The size advantage model of sex allocation in the protandrous sex-changer Crepidula fornicata: role of the mating system, sperm storage, and male mobility

Sequential hermaphroditism is adaptive when the reproductive value of an individual varies with size or age, and this relationship differs between males and females. In this case, theory shows that the lifetime reproductive output of an individual is increased by changing sex (a hypothesis referred to as the size-advantage model). Sex-linked differences in size-fitness curves can stem from differential costs of reproduction, the mating system, and differences in growth and mortality between sexes. Detailed empirical data is required to disentangle the relative roles of each of these factors within the theory. Quantitative data are also needed to explore the role of sperm storage, which has not yet been considered with sequential hermaphrodites. Using experimental rearing and paternity assignment, we report relationships between size and reproductive success of Crepidula fornicata, a protandrous (male-first) gastropod. Male reproductive success increased with size due to the polygamous system and stacking behavior of the species, but females nonetheless had greater reproductive success than males of the same size, in agreement with the size-advantage theory. Sperm storage appeared to be a critical determinant of success for both sexes, and modeling the effect of sperm storage showed that it could potentially accelerate sex change in protandrous species.

当个体的繁殖价值随体型或年龄发生变化，且雌雄两性间该变化关系存在差异时，顺序雌雄同体（sequential hermaphroditism）便具备适应性优势。此时相关理论表明，个体通过改变性别可提升终生繁殖产出（该假说被称为体型优势模型（size-advantage model））。体型-适合度曲线的性别间差异，可源于繁殖成本差异、交配系统以及两性间生长与死亡率的不同。要厘清该理论框架下各因素的相对作用，需借助详实的实证数据。针对目前尚未在顺序雌雄同体物种研究中纳入考量的精子储存作用，同样需要定量数据展开探究。本研究通过实验饲养与父权鉴定技术，报道了雄性先熟（protandrous，雄性优先型）腹足纲动物——履螺（Crepidula fornicata）的体型与繁殖成功间的关联。该物种的多配偶交配系统与堆叠栖息行为，使得雄性繁殖成功率随体型增大而提升；但即便如此，相同体型下雌性的繁殖成功率仍高于雄性，这与体型优势模型的理论预测相符。精子储存似乎是两性繁殖成功的关键决定因素，而针对精子储存效应的建模结果显示，其或可加速雄性先熟物种的性转变过程。