Data from: Birth date predicts alternative life-history pathways in a fish with sequential reproductive tactics

In species with plastic expression of alternative reproductive tactics (ARTs), individuals of the same sex, usually males, can adopt different reproductive tactics depending on factors such as body size. The ‘birth date hypothesis’ proposes that condition-dependent expression of ARTs may ultimately depend on birth date, because individuals born at different times of the year may achieve different sizes and express different reproductive tactics accordingly. However, this has rarely been tested. Here, we tested this hypothesis in a fish with ARTs, the peacock blenny (Salaria pavo). A long-term (6 years) mark–recapture study demonstrated that ARTs in the peacock blenny were sequential and that males may follow at least two alternative life-history pathways: a nest-holder pathway, in which males express the nest-holder tactic from their first breeding season onwards, and a parasitic pathway, where males reproduce on their first breeding season as sneaker males and subsequently as nest-holders. We have found evidence of a birth date effect on the expression of ARTs in the peacock blenny. Males following the nest-holder pathway are born earlier and are larger at the first breeding season than males following the parasitic pathway, but they have similar growth curves. The mechanisms underlying a birth date effect are far from clear and might be diverse. We have not found support for a mechanism of body size threshold triggering sexual maturation and subsequent ARTs. A mechanism of tactic determination that is strictly based on timing of first maturation is also unlikely. A proxy of lifetime reproductive success shows crossing (body size associated) fitness curves for the two main life-history pathways.在具有替代繁殖策略（alternative reproductive tactics, ARTs）可塑性表达的物种中，同一性别（通常为雄性）的个体可依据体型大小等因素采取不同的繁殖策略。‘出生日期假说’（birth date hypothesis）认为，依赖于个体状态的替代繁殖策略表达最终可能取决于出生日期：一年中不同时段出生的个体，其最终体型可能存在差异，进而采取不同的繁殖策略。然而，该假说此前鲜有得到验证。本研究针对具有替代繁殖策略分化的鱼类——花鳚（Salaria pavo）对该假说展开了检验。一项为期6年的长期标记重捕（mark–recapture）研究证实，花鳚的替代繁殖策略具有序列性，雄性至少存在两种不同的生活史路径：其一为筑巢者路径，即雄性自首个繁殖季起便采取筑巢者繁殖策略；其二为寄生路径，即雄性在首个繁殖季便以偷配雄鱼（sneaker males）的身份完成繁殖，后续再转为筑巢者。本研究发现，花鳚的替代繁殖策略表达存在出生日期效应：采取筑巢者路径的雄性，其出生时间更早，且在首个繁殖季时的体型大于采取寄生路径的雄性，但二者的生长曲线并无显著差异。介导出生日期效应的具体机制仍未明确，且可能具有多样性。本研究未发现支持‘体型阈值触发性成熟及后续替代繁殖策略表达’这一机制的证据，严格基于首次性成熟时间来决定繁殖策略的机制也可能性较低。针对两种主要生活史路径的终身繁殖成功率（lifetime reproductive success）代用指标显示，二者的适合度曲线（fitness curves）存在交叉，且该交叉与体型大小相关。