Data from: Benefits of polyandry: molecular evidence from field-caught dung beetles

When females mate with multiple males, they set the stage for post-copulatory sexual selection via sperm competition and/or cryptic female choice. Surprisingly little is known about the rates of multiple mating by females in the wild, despite the importance of this information in understanding the potential for post-copulatory sexual selection to drive the evolution of reproductive behavior, morphology, and physiology. Dung beetles in the genus <i>Onthophagus</i> have become a laboratory model for studying pre- and post-copulatory sexual selection, yet we still lack information about the reproductive behavior of female dung beetles in natural populations. Here, we develop microsatellite markers for <i>Onthophagus taurus</i>, and use them to genotype the offspring of wild-caught females, and to estimate natural rates of multiple mating and patterns of sperm utilization. We found that <i>O. taurus</i> females are highly polyandrous: 88% of females produced clutches sired by at least two males, and 5% produced clutches with as many as five sires. Several females (23%) produced clutches with significant paternity skew, indicating the potential for strong post-copulatory sexual selection in natural populations. There were also strong positive correlations between the number of offspring produced and both number of fathers and paternity skew, which suggests that females benefit from mating polyandrously by inciting post-copulatory mechanisms that bias paternity towards males that can sire more viable offspring. This study evaluates the fitness consequences of polyandry for an insect in the wild, and provides strong evidence that female dung beetles benefit from multiple mating under natural conditions.

当雌性个体与多个雄性交配时，便为通过精子竞争（sperm competition）和/或隐蔽雌性选择（cryptic female choice）实现的交配后性选择（post-copulatory sexual selection）奠定了作用基础。令人意外的是，尽管此类信息对理解交配后性选择推动生殖行为、形态与生理演化的潜在潜力至关重要，但学界对野生种群中雌性多次交配的发生率仍知之甚少。蜣螂属（Onthophagus）昆虫已成为研究交配前与交配后性选择的经典实验模型，但我们仍缺乏自然种群中雌性蜣螂生殖行为的相关数据。本研究开发了金牛座蜣螂（Onthophagus taurus）的微卫星标记（microsatellite markers），并利用该标记对野外捕获雌性的后代进行基因分型，以此估算其自然种群中的多次交配率与精子利用模式。研究结果显示，金牛座蜣螂雌性具有高度的一妻多夫特性：88%的雌性所产卵块至少由两只雄性授精，另有5%的卵块最多可由五只雄性授精。其中23%的雌性所产卵块存在显著的父权偏倚（paternity skew），这表明自然种群中存在较强的交配后性选择潜力。此外，雌性产生的后代数量与雄性父本数量、父权偏倚均呈显著正相关，这暗示雌性通过一妻多夫交配，可激活交配后机制，使受精偏向于能产生更具生存力后代的雄性，从而从中获益。本研究评估了野生昆虫一妻多夫策略的适合度后果（fitness consequences），为自然条件下雌性蜣螂从多次交配中获益提供了强有力的实证支持。