Variation in Apical Hook Length Reflects the Intensity of Sperm Competition in Murine Rodents

Martin Šandera,Tomáš Albrecht,Pavel Stopka,Simone Immler

doi:10.1371/journal.pone.0068427

Martin Šandera, Tomáš Albrecht + Show 2 more

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https://doi.org/10.1371/journal.pone.0068427

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Abstract

BackgroundPost-copulatory sexual selection has been shown to shape morphology of male gametes. Both directional and stabilizing selection on sperm phenotype have been documented in vertebrates in response to sexual promiscuity.MethodologyHere we investigated the degree of variance in apical hook length and tail length in six taxa of murine rodents.ConclusionsTail sperm length and apical hook length were positively associated with relative testis mass, our proxy for levels of sperm competition, thus indicating directional post-copulatory selection on sperm phenotypes. Moreover, our study shows that increased levels of sperm competition lead to the reduction of variance in the hook length, indicating stabilizing selection. Hence, the higher risk of sperm competition affects increasing hook length together with decreasing variance in the hook length. Species-specific post-copulatory sexual selection likely optimizes sperm morphology.

Highlights

Sperm competition and other postcopulatory processes have been considered as important evolutionary selective forces [1], [2], [3]
The most variable hook length was found in M. domesticus, the least variable in A. agrarius and in A. sylvaticus
Sperm of M. musculus showed the largest variation in the tail length and the relative testis weight differed significantly between the species studied (Anova, F(5,46) = 88.684, p,0.001)

Summary

Introduction

Sperm competition and other postcopulatory processes have been considered as important evolutionary selective forces [1], [2], [3]. It has been shown that some sperm traits indicate the risk of sperm competition [9] and could be influenced by directional [11], [15] and/or stabilizing selection [11], [16]. Sperm competition acts to reduce between-male and withinmale variation in sperm length in various animal taxa, including birds [19], [12], [16] and hymenopterans [13], possibly through an increase in strength of post-copulatory selection on sperm traits [20], [11]. Post-copulatory sexual selection has been shown to shape morphology of male gametes Both directional and stabilizing selection on sperm phenotype have been documented in vertebrates in response to sexual promiscuity

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