Data from: The more the better – polyandry and genetic similarity are positively linked to reproductive success in a natural population of terrestrial salamanders (Salamandra salamandra)

Although classically thought to be rare, female polyandry is wide-spread and may entail significant fitness benefits. If females store sperm over extended periods of time, the consequences of polyandry will depend on the pattern of sperm storage, and some of the potential benefits of polyandry can only be realized if sperm from different males is mixed. Our study aimed to determine patterns and consequences of polyandry in an amphibian species, the fire salamander, under fully natural conditions. Fire salamanders are ideal study objects, since mating, fertilisation and larval deposition are temporally decoupled, females store sperm for several months and larvae are deposited in the order of fertilization. Based on 18 microsatellite loci, we conducted paternity analysis of 24 female-offspring arrays, with, in total, over 600 larvae fertilised under complete natural conditions. More than one third of females were polyandrous and up to four males were found as sires. Our data clearly show that sperm from multiple males is mixed in the female's spermatheca. Nevertheless, paternity is biased, and the most successful male sires on average 70% of the larvae, suggesting a “topping off” mechanism with first-male precedence. Female reproductive success increased with the number of sires, most likely because multiple mating ensured high fertilization success. In contrast, offspring number was unaffected by female condition and genetic characteristics, but surprisingly, it increased with the degree of genetic relatedness between females and their sires. Sires of polyandrous females tended to be genetically similar to each other, indicating a role for active female choice.

尽管学界传统观点认为雌性一妻多夫制（polyandry）较为罕见，但该现象实则广泛存在，且可带来显著的适合度收益。若雌性能够长期储存精子，一妻多夫制的演化后果将取决于精子储存模式；唯有当不同雄性的精子发生混合时，一妻多夫制的部分潜在收益才能得以实现。本研究以两栖动物火蝾螈（fire salamander）为研究对象，旨在探究其在完全自然条件下的一妻多夫制模式及其演化后果。火蝾螈是理想的研究模型，因其交配、受精与幼体排放在时间上相互分离：雌性可储存精子达数月之久，且幼体的排放顺序与受精顺序完全一致。本研究基于18个微卫星位点（microsatellite loci），对24组雌性-后代样本进行了父权分析，总计分析了600余尾在完全自然条件下受精的幼体。超过三分之一的雌性个体存在一妻多夫现象，最多可检测到4个父本。我们的数据清晰表明，来自多个雄性的精子会在雌性的纳精囊（spermatheca）内发生混合。尽管如此，父权分配仍存在偏倚：最成功的父本平均可使70%的幼体获得父权，这提示存在一种“补充受精”（topping off）机制，且伴随首父优先（first-male precedence）效应。雌性的繁殖成功率随父本数量的增加而提升，这很可能是因为多次交配确保了较高的受精成功率。与之相反，幼体数量不受雌性自身状态与遗传特征的影响，但令人意外的是，其数量随雌性与其父本之间的遗传相关性升高而增加。一妻多夫雌性的多个父本之间往往遗传相似性较高，这表明雌性存在主动的配偶选择行为。