Abstract

Size-assortative pairing is common across a wide range of taxa. In many cases, both sexes would benefit from pairing with a mate larger than themselves. As males and females cannot simultaneously be larger than their pair mate, size differences within pairs reflect which sex is able to obtain this benefit. Snapping shrimp can be found in pairs year-round, and both males and females would benefit from pairing with larger individuals. Larger females are more fecund; males, then, are likely to benefit from pairing with larger females primarily in the reproductive season. Larger individuals are more successful competitors and females benefit more from shared burrow defense than males; for females, then, benefits of pairing with larger males are likely to accrue year-round. In this study, we use field data to test whether within-pair size differences in snapping shrimp correspond more to male or female interests, and whether this outcome differs between seasons. We find that size-assortative pairing varies seasonally: although body sizes of paired males and females are highly correlated year-round, the within-pair size difference is greater during the reproductive season than the nonreproductive season. Furthermore, within pairs, females are larger than males during the reproductive season, while pairs are size-matched or male-biased during the nonreproductive season. These changes in within-pair size relationships suggest seasonal differences in which sex has greater control over pair formation, and highlight nonreproductive benefits associated with monogamous pairing. In addition, these results underscore the importance of considering temporal variation in studies of size-assortative pairing.

Significance statement

In many taxa, it is advantageous for both males and females to mate with larger individuals. As both sexes cannot simultaneously mate with larger individuals, size relationships within pairs reflect the outcome of this sexual conflict. In snapping shrimp, pairs cooperate in defending their burrows from invading conspecifics, and larger individuals are better competitors; larger females are also more fecund. Thus, males obtain a reproductive advantage from mating with larger females, while for females, mating with larger males provides social (territorial defense) benefits. Here, we find seasonal differences in within-pair size relationships, such that females are larger than males during the reproductive season, but pairs in the nonreproductive season are size-matched or male-biased. These results suggest seasonal variation in the outcome of conflict over body size within pairs, and highlights the need to consider temporal variation in size-assortative pairing.

中文翻译：

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这是季节的时间：性冲突的大小分类配对的季节性变化

摘要

大小分类配对在广泛的分类群中很常见。在许多情况下，两性都会受益于与比自己大的配偶配对。由于雄性和雌性不能同时大于它们的配偶，因此对内的大小差异反映了哪个性别能够获得这种好处。捕虾全年都可以成对出现，雄性和雌性都可以从与较大的个体配对中受益。较大的雌性繁殖力更强；因此，雄性可能会受益于主要在生殖季节与较大的雌性配对。较大的个体是更成功的竞争者，雌性比雄性更能从共同的洞穴防御中受益；因此，对于女性来说，与较大的男性配对的好处可能会全年累积。在这项研究中，我们使用现场数据来测试捕捉虾的对内大小差异是否更符合雄性或雌性的兴趣，以及这种结果是否在季节之间有所不同。我们发现尺寸分类配对随季节变化：尽管配对的雄性和雌性的体型全年高度相关，但在繁殖季节，配对内尺寸差异大于非繁殖季节。此外，在成对中，雌性在繁殖季节比雄性大，而在非繁殖季节成对大小匹配或偏向雄性。这些成对内大小关系的变化表明性别对成对形成有更大的控制的季节性差异，并突出了与一夫一妻制配对相关的非生殖益处。此外，

意义陈述

在许多分类群中，雄性和雌性与较大的个体交配都是有利的。由于两性不能同时与较大的个体交配，因此配对内的大小关系反映了这种性冲突的结果。在捕虾过程中，成对合作保护它们的洞穴免受同种物种的入侵，而较大的个体是更好的竞争者；较大的雌性也更肥沃。因此，雄性通过与较大的雌性交配获得生殖优势，而对于雌性而言，与较大的雄性交配提供社会（领土防御）益处。在这里，我们发现了配对内大小关系的季节性差异，例如在生殖季节女性比男性大，但在非生殖季节的配对是大小匹配或偏向男性的。