Extra-group paternity, in which offspring are sired by a male outside the breeding group, may alter the distribution of reproductive success in a population, thus affecting the opportunity for sexual selection. Both inter- and intraspecific studies have focused largely on mating systems in which females choose their social mates, and less is known about extra-group paternity in polygynous systems in which social mates are largely dictated by male-male competition. In this study, we examine the frequency and distribution of extra-group paternity in a harem-forming bat, Phyllostomus hastatus. We find that despite aggressive harem defense, males are unable to fully monopolize reproduction within their harem and over 70% of harems contain extra-group offspring. Harem males in better body condition suffered less paternity loss, but we found no effect of male age or body size. Even though the age and size of individual females did not predict offspring paternity, we found a significant effect of age heterogeneity within the group. Harems composed of differently aged females were more likely to contain extra-group offspring. Our results not only provide evidence for the role of male defense in preventing extra-group paternity but also suggest that social group composition has consequences for male reproductive success. In polygynous societies, the ability to monopolize mating is critical to reproductive success. As the group size increases, defense often becomes more difficult, resulting in increased rates of extra-group paternity. We find that among greater spear-nosed bats, extra-group offspring occur in most harems, but the overall rate of extra-group paternity is relatively low despite their large harems (15–30 females). Variation in the rate of extra-group paternity between harems is explained by male body condition (i.e., relative mass) but not harem size. Additionally, the rate of extra-group paternity is not explained entirely by male attributes, as we find that age heterogeneity within the female group is a significant predictor of the extra-group paternity rate. Our results support the hypothesis that not only the physical condition of a male influences his ability to monopolize reproduction but also the group composition influences the female mating behavior.

中文翻译：

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雄性状况和群体异质性可预测新热带蝙蝠的群体外亲子关系

异群父系，即后代由繁殖群之外的雄性所生，可能会改变种群中繁殖成功率的分布，从而影响性选择的机会。种间和种内研究都主要集中在女性选择社交伴侣的交配系统上，而对一夫多妻制系统中的群外父子关系知之甚少，在这种系统中，社交伴侣主要由男性-男性竞争决定。在这项研究中，我们检查了形成后宫的蝙蝠 Phyllostomus hastatus 中异族亲子关系的频率和分布。我们发现，尽管具有侵略性的后宫防御，但雄性无法完全垄断后宫内的繁殖，并且超过 70% 的后宫包含群外后代。身体状况较好的后宫男性失去亲子关系较少，但我们没有发现男性年龄或体型的影响。尽管个体女性的年龄和体型不能预测后代的亲子关系，但我们发现了群体内年龄异质性的显着影响。由不同年龄的女性组成的后宫更有可能包含额外的后代。我们的研究结果不仅为男性防御​​在防止异族父子关系中的作用提供了证据，而且还表明社会群体构成对男性生殖成功有影响。在一夫多妻制的社会中，垄断交配的能力对于繁殖成功至关重要。随着群体规模的增加，防御往往变得更加困难，导致额外群体亲子关系的比率增加。我们发现在较大的矛鼻蝙蝠中，大多数后宫中都出现了群外后代，但是，尽管他们的后宫很大（15-30 名女性），但总体外父子关系的比率相对较低。后宫之间异族亲子关系的变化是由男性身体状况（即相对质量）而不是后宫大小来解释的。此外，组外亲子关系的比率并不能完全由男性属性解释，因为我们发现女性组内的年龄异质性是组外亲子关系的重要预测因素。我们的结果支持这样一个假设，即不仅雄性的身体状况会影响其垄断繁殖的能力，而且群体组成也会影响雌性的交配行为。此外，组外亲子关系的比率并不能完全由男性属性解释，因为我们发现女性组内的年龄异质性是组外亲子关系的重要预测因素。我们的结果支持这样一个假设，即不仅雄性的身体状况会影响其垄断繁殖的能力，而且群体组成也会影响雌性的交配行为。此外，组外亲子关系的比率并不能完全由男性属性解释，因为我们发现女性组内的年龄异质性是组外亲子关系的重要预测因素。我们的结果支持这样一个假设，即不仅雄性的身体状况会影响其垄断繁殖的能力，而且群体组成也会影响雌性的交配行为。