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

1. 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. 2. The “birthdate hypothesis” proposes that condition dependent expression of ARTs may ultimately depend on birthdate, 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. 3. 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 weresequential 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. 4. We have found evidence of a birthdate 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. 5. The mechanisms underlying a birthdate 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. 6. A proxy of lifetime reproductive success shows crossing (body size associated) fitness curves for the two main life-history pathways.

1. 在具有替代性繁殖策略（Alternative Reproductive Tactics）可塑性表达的物种中，同一性别的个体（通常为雄性）可根据体型等因素采取不同的繁殖策略。
2. “出生时间假说”提出，依赖于个体状态的替代性繁殖策略表达最终可能取决于出生时间：一年中不同时段出生的个体可能达到不同的体型，并据此表现出不同的繁殖策略。然而，该假说极少得到检验。
3. 本研究以具有替代性繁殖策略的鱼类——孔雀鳚（Salaria pavo）为对象，对该假说开展了检验。一项为期6年的长期标记重捕研究表明，孔雀鳚的替代性繁殖策略具有连续性，雄性至少可遵循两种替代性生活史路径：其一为筑巢者路径，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，雄性在首个繁殖季以偷袭型雄性（Sneaker Males）身份繁殖，后续则转变为筑巢者。
4. 本研究发现，孔雀鳚的替代性繁殖策略表达存在出生时间效应。相较于遵循寄生路径的雄性，遵循筑巢者路径的雄性出生更早，且在首个繁殖季体型更大，但二者的生长曲线并无显著差异。
5. 出生时间效应背后的机制尚不明确，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性繁殖策略表达”这一机制的证据，严格基于首次性成熟时间的策略决定机制也缺乏合理性。
6. 一项终生繁殖成功率的替代指标显示，两种主要生活史路径的适合度曲线存在交叉（与体型相关）。