Document Type

Article

Department/Program

Virginia Institute of Marine Science

Publication Date

2015

Journal

Proceedings Of The Royal Society B-Biological Sciences

Volume

282

Issue

1809

Abstract

Sexual dimorphism is typically a result of strong sexual selection on male traits used in male male competition and subsequent female choice. However, in social species where reproduction is monopolized by one or a few individuals in a group, selection on secondary sexual characteristics may be strong in both sexes. Indeed, sexual dimorphism is reduced in many cooperatively breeding vertebrates and eusocial insects with totipotent workers, presumably because of increased selection on female traits. Here, we examined the relationship between sexual dimorphism and sociality in eight species of Synalpheus snapping shrimps that vary in social structure and degree of reproductive skew. In species where reproduction was shared more equitably, most members of both sexes were physiologically capable of breeding. However, in species where reproduction was monopolized by a single individual, a large proportion of females but not males-were reproductively inactive, suggesting stronger reproductive suppression and conflict among females. Moreover, as skew increased across species, proportional size of the major chela-the primary antagonistic weapon in snapping shrimps increased among females and sexual dimorphism in major chela size declined. Thus, as reproductive skew increases among Synalpheus, female female competition over reproduction appears to increase, resulting in decreased sexual dimorphism in weapon size.

DOI

10.1098/rspb.2015.0342

Keywords

Cooperative Mammals; Social Competition; Queen Replacement; Evolution; Selection; Eusociality; Synalpheus; Conflict; Female; Termites

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