In polygamy, individuals interact in a non-random manner to shape reproductive networks. However, relative importance of behavior versus individual physical traits (e.g., body size) in determining access to partners and reproductive success varies by species and is poorly understood in small-bodied aquatic species for which direct observations are challenging in the wild. Here, we coupled automated individual tracking and genetic parentage techniques to characterize reproductive networks and their consequences on reproductive success in bluehead chub (Nocomis leptocephalus), a nest-building stream fish native to the southeastern USA. Fish were marked with 12-mm passive integrated transponder (PIT) tags, and loop-shaped PIT antennas were deployed around 18 nests to monitor behavioral encounters of 311 individuals (34 males and 277 females and immature males) during the spawning season in 2017. After spawning, genetic samples of 326 young-of-the-year fish (i.e., offspring) were collected. The mating system was polygynandrous, and factors affecting access to partners and reproductive success differed between males and females. Male body size did not affect number of encounters with females and reproductive success, instead behavior indexing reproductive effort (number and size of nests occupied) explained variation in reproductive success. On the contrary, body size was a key determinant of female reproductive success. Fecundity (i.e., number of eggs) increased with body size, and higher encounters rates withmales did not result in higher reproductive success. In males and females, mating with more partners led to higher reproductive success, which may have contributed to the evolution and maintenance of polygynandry in this species. Significance statement Is bigger better? This question has been investigated with respect to animal mating behavior and reproductive success, and the answer appears to vary by species. Using an intensive individual-based approach with PIT antenna and molecular markers, we show that behavior outweighed body size in mediating reproductive success of males but not females of a nest-building stream fish. Males increased access to females and ultimately number of offspring by occupying larger andmore nests, which are proxies of reproductive effort. In females, body size was more important than behavior in determining reproductive success, and behavior explained much less of variation in reproductive success. Diverse and complex reproductive patterns of males may explain why behavior outweighed body size in mediating reproductive success, a hypothesis that warrants further research across species with a gradient of mating systems and behavioral complexities.

中文翻译：

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行为超过体型在介导筑巢鱼蓝头鲢雄性繁殖成功方面的作用

在一夫多妻制中，个体以非随机的方式互动以塑造生殖网络。然而，行为与个体身体特征（例如，体型）在确定获得伴侣和繁殖成功方面的相对重要性因物种而异，并且在野外直接观察具有挑战性的小型水生物种中知之甚少。在这里，我们结合自动个体跟踪和遗传亲子关系技术来表征繁殖网络及其对蓝头鲢（Nocomis leptocephalus）繁殖成功的影响，蓝头鲢（Nocomis leptocephalus）是一种原产于美国东南部的筑巢溪鱼。鱼标有 12 毫米无源集成转发器 (PIT) 标签，在 2017 年产卵季节，在 18 个巢周围部署环形 PIT 天线，监测 311 条个体（34 条雄性和 277 条雌性和未成熟雄性）的行为遭遇。 产卵后，326 条幼鱼的遗传样本（即后代）被收集。交配系统是一夫多妻的，影响获得伴侣和繁殖成功的因素在男性和女性之间有所不同。雄性体型不影响与雌性相遇的次数和繁殖成功率，相反，行为指数繁殖努力（占据的巢穴的数量和大小）解释了繁殖成功率的变化。相反，体型是女性繁殖成功的关键决定因素。繁殖力（即卵数）随着体型的增加而增加，与雄性的更高相遇率并没有导致更高的繁殖成功率。在雄性和雌性中，与更多伴侣交配导致更高的繁殖成功率，这可能有助于该物种的一夫多妻制的进化和维持。意义说明越大越好吗？这个问题已经就动物交配行为和繁殖成功进行了研究，答案似乎因物种而异。使用具有 PIT 天线和分子标记的基于个体的强化方法，我们表明在介导筑巢溪流鱼的雄性而非雌性的繁殖成功方面，行为的重要性超过了体型。雄性通过占据更大和更多的巢穴来增加与雌性以及最终后代数量的接触，巢穴是繁殖努力的代表。在女性中，在决定繁殖成功率方面，体型比行为更重要，而行为对繁殖成功率的影响要小得多。雄性多样化和复杂的生殖模式可以解释为什么行为在调节生殖成功方面的重要性超过了体型，这一假设需要对具有交配系统和行为复杂性梯度的物种进行进一步研究。