Many animal species exhibit multiple paternity, defined as multiple males genetically contributing to a single female reproductive event, such as a clutch or litter. Although this phenomenon is well documented across a broad range of taxa, the underlying causes and consequences remain poorly understood. For example, it is unclear how multiple paternity correlates with life-history strategies. Furthermore, males and females may differ in mating strategies and these patterns may shift with ecological context and life-history variation. Here, we take advantage of natural life-history variation in garter snakes (Thamnophis elegans) to address these questions in a robust field setting where populations have diverged along a slow-to-fast life-history continuum. We determine both female (observed) and male (using molecular markers) reproductive success in replicate populations of 2 life-history strategies. We find that despite dramatic differences in annual female reproductive output: 1) females of both life-history ecotypes average 1.5 sires per litter and equivalent proportions of multiply-sired litters, whereas 2) males from the slow-living ecotype experience greater reproductive skew and greater variance in reproductive success relative to males from the fast-living ecotype males despite having equivalent average reproductive success. Together, these results indicate strong intrasexual competition among males, particularly in the fast-paced life-history ecotype. We discuss these results in the context of competing hypotheses for multiple paternity related to population density, resource variability, and life-history strategy.

中文翻译：

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具有进化不同生活史的吊袜带蛇的多重亲子关系

许多动物物种表现出多重亲子关系，定义为多个雄性在遗传上对单个雌性生殖事件有贡献，例如一窝或一窝。尽管这种现象在广泛的分类群中都有很好的记录，但其根本原因和后果仍然知之甚少。例如，尚不清楚多重亲子关系与生活史策略之间的关系。此外，雄性和雌性的交配策略可能不同，这些模式可能会随着生态环境和生活史的变化而变化。在这里，我们利用吊袜带蛇（Thamnophis elegans）的自然生活史变异来解决这些问题，在一个稳健的野外环境中，种群沿着从慢到快的生活史连续体分化。我们确定了女性（观察到的）和男性（使用分子标记）在 2 种生活史策略的复制人群中的繁殖成功率。我们发现，尽管每年雌性生殖产量存在显着差异：1) 两种生活史生态型的雌性平均每窝 1.5 头公牛和相当比例的多胎产仔，而 2) 来自缓慢生活生态型的雄性经历更大的生殖偏斜和尽管具有相同的平均繁殖成功率，但与快速生活生态型雄性的雄性相比，繁殖成功率的差异更大。总之，这些结果表明男性之间存在强烈的性内竞争，特别是在快节奏的生活史生态型中。我们在与人口密度、资源可变性、