Data from: Brood-tending males in a biparental fish suffer high paternity losses but rarely cuckold

Extra-pair paternity within socially monogamous mating systems is well-studied in birds and mammals but rather neglected in other animal taxa. In fishes, social monogamy has evolved several times but few studies have investigated the extent to which pair-bonded male fish lose fertilizations to cuckolders and gain extra-pair fertilizations themselves. We address this gap and present genetic paternity data collected from a wild population of Variabilichromis moorii, a socially monogamous African cichlid with biparental care of offspring. We show that brood-tending, pair-bonded males suffer exceptionally high paternity losses, siring only 63% of the offspring produced by their female partners on average. The number of cuckolders per brood ranged up to nine and yet, surprisingly, brood-tending males in the population were rarely the culprits. Brood-tending males sired very few extra-pair offspring, despite breeding in close proximity to one another. While unpaired males were largely responsible for the cuckoldry, pair-bonded males still enjoyed higher fertilization success than individual unpaired males. We discuss these results in the context of ecological and phenotypic constraints on cuckoldry and the fitness payoffs of alternative male tactics. Our study provides new insights into how pair-bonded males handle the trade-off between securing within-pair and extra-pair reproduction.

社会一夫一妻制交配体系中的额外配对父权（extra-pair paternity）已在鸟类和哺乳类中得到充分研究，但在其他动物类群中却颇受忽视。在鱼类中，社会一夫一妻制已多次独立演化，但鲜有研究探讨配对结合的雄性鱼类会在多大程度上被盗精者窃取受精机会，以及自身获得额外配对受精的情况。针对这一研究空白，我们展开了相关研究，并呈现了采自野生种群的遗传父权数据——该种群为实行双亲育幼的社会一夫一妻制非洲慈鲷莫瑞柔丽鲷（Variabilichromis moorii）。研究结果显示，承担育幼职责的配对雄性父权损失极高，平均仅能使雌性伴侣所产后代中的63%携带自身遗传物质。每窝幼体的盗精者数量最多可达9只，但令人意外的是，该种群中的育幼雄性极少充当盗精者。尽管雄性个体的繁殖领地彼此邻近，育幼雄性几乎无法获得额外配对受精的机会。未配对雄性是盗精行为的主要实施者，但配对雄性的受精成功率仍高于单个未配对雄性。我们结合盗精行为所受的生态与表型约束，以及雄性替代繁殖策略的适合度收益，对上述结果展开了讨论。本研究为配对雄性如何权衡保障配对内繁殖与获取额外配对繁殖机会的问题提供了新的见解。