Del Matto Lygia A, Macedo-Rego Renato C, Santos Eduardo S A
BECO do Departamento de Zoologia, Universidade de São Paulo, Sao Paulo, Brazil.
Programa de Pós-Graduação em Zoologia, Universidade de São Paulo, Sao Paulo, Brazil.
PeerJ. 2021 Oct 22;9:e12310. doi: 10.7717/peerj.12310. eCollection 2021.
Males are expected to mate with as many females as possible, but can maximize their reproductive success through strategic mating decisions. For instance, males can increase their own fitness by mating with high quality females that produce more offspring. Additionally, males can adjust mating effort based on the relative distribution of females and male competitors. To test factors that influence male mate choice, we assessed male mating decisions in the golden silk orb-weaver spider, (Nephilidae), a species in which females are polyandrous, males guard females before and after copulation occurs and large males are the most successful at guarding mates. We tested the hypothesis that males spend more time guarding high quality females that are spatially isolated, and when the risk of sperm competition is higher. We also hypothesized that this effect increases with male body size. We assessed solitary and aggregated female webs in the field and quantified female quality (, female body condition), male size (, male body size), the risk of sperm competition (, number of males in each female web), and mate-guarding duration (, number of days each male spent in each web). We found that mate-guarding behaviour is largely influenced by the presence of male competitors. In addition, male body size seems to moderately influence male guarding decisions, with larger males guarding for a longer time. Finally, female body condition and type of web (, solitary or aggregated) seem to play small roles in mate-guarding behaviour. As mate-guarding duration increased by 0.718 day per each additional male competitor in the web, and guarding behaviour prevents males from seeking additional mates, it seems that guarding females can be considerably costly. We conclude that failing to guard a sexual partner promotes high costs derived from sperm competition, and a male cannot recover his relative loss in fertilization success by seeking and fertilizing more females. In addition, the search for more sexual partners can be constrained by possible high costs imposed by weight loss and fights against other males, which may explain why the type of web only moderately influenced male mate choice. Following the same rationale, if high-quality females are not easy to find and/or mating with a high-quality female demands much effort, males may search females and guard them regardless of female quality. In conclusion, the factor that most influences male mate-guarding behaviour among in the field is the risk of sperm competition.
雄性被期望与尽可能多的雌性交配，但它们可以通过策略性的交配决策来最大化自己的繁殖成功率。例如，雄性通过与能产生更多后代的高质量雌性交配来提高自身的适应性。此外，雄性可以根据雌性和雄性竞争者的相对分布来调整交配投入。为了测试影响雄性配偶选择的因素，我们评估了金丝圆蛛（Nephilidae）的雄性交配决策，在这个物种中，雌性会与多个雄性交配，雄性在交配前后都会守护雌性，并且体型大的雄性在守护配偶方面最成功。我们测试了以下假设：雄性会花更多时间守护空间上孤立的高质量雌性，以及在精子竞争风险更高的时候。我们还假设这种影响会随着雄性体型的增大而增强。我们在野外评估了独居和聚集的雌性蛛网，并量化了雌性质量（即雌性身体状况）、雄性体型（即雄性身体大小）、精子竞争风险（即每个雌性蛛网中的雄性数量）以及配偶守护持续时间（即每个雄性在每个蛛网中花费的天数）。我们发现，配偶守护行为在很大程度上受雄性竞争者的存在影响。此外，雄性体型似乎对雄性的守护决策有一定影响，体型较大的雄性守护时间更长。最后，雌性身体状况和蛛网类型（即独居或聚集）在配偶守护行为中似乎起的作用较小。由于每个额外的雄性竞争者会使配偶守护持续时间增加0.718天，并且守护行为会阻止雄性寻找其他配偶，看来守护雌性的代价可能相当高昂。我们得出结论，未能守护性伴侣会因精子竞争而带来高昂代价，并且雄性无法通过寻找更多雌性交配并使其受精来弥补其在受精成功率方面的相对损失。此外，寻找更多性伴侣可能会受到体重减轻和与其他雄性争斗可能带来的高昂代价的限制，这也许可以解释为什么蛛网类型对雄性配偶选择的影响只是适度的。按照同样的逻辑，如果高质量雌性不容易找到和/或与高质量雌性交配需要付出很多努力，雄性可能会寻找雌性并守护它们，而不考虑雌性质量。总之，在野外环境中，对雄性配偶守护行为影响最大的因素是精子竞争风险。
