Kin but less than kind: within-group male relatedness does not increase female fitness in seed beetles.

Elena C Berg,Shannon Monahan,Alexei A Maklakov,Martin I Lind,Sophie Bricout

doi:10.1098/rspb.2019.1664

Abstract

Theory maintains within-group male relatedness can mediate sexual conflict by reducing male–male competition and collateral harm to females. We tested whether male relatedness can lessen female harm in the seed beetle Callosobruchus maculatus. Male relatedness did not influence female lifetime reproductive success or individual fitness across two different ecologically relevant scenarios of mating competition. However, male relatedness marginally improved female survival. Because male relatedness improved female survival in late life when C. maculatus females are no longer producing offspring, our results do not provide support for the role of within-group male relatedness in mediating sexual conflict. The fact that male relatedness improves the post-reproductive part of the female life cycle strongly suggests that the effect is non-adaptive. We discuss adaptive and non-adaptive mechanisms that could result in reduced female harm in this and previous studies, and suggest that cognitive error is a likely explanation.

Highlights

Males and females have different routes to successful reproduction [1], and this can lead to evolutionary conflict between the sexes [2,3,4]
Male mate harm occurs in many animals and has been especially well studied in insects, including the bed bug Cimex lectularius, the seed beetle Callosobruchus maculatus and the fruit fly Drosophila melanogaster
We investigated the effect of male relatedness and familiarity in a large outbred and welldescribed population of C. maculatus (SI USA) that was not provided with yeast in the adult stage, which is in line with the recent evolutionary history of this species and this population

Summary

Introduction

Males and females have different routes to successful reproduction [1], and this can lead to evolutionary conflict between the sexes [2,3,4]. As Chippindale et al [28] point out, for this kind of kin selection to occur, three conditions must be met: (i) males must harm their mates in some way, thereby reducing female reproductive success; (ii) there must be some mechanism in place for reliably recognizing kin; and (iii) groups of related males must have a reasonable chance of encountering each other during the reproductive period Another possibility for reduced harm to females is familiarity among males raised together that can lead to reduced levels of aggression [29]. A later study by Le Page et al [32] suggested that when males are both related and familiar to each other, they cause reduced female harm in D. melanogaster These conflicting results suggest that it remains unclear what role within-group male relatedness plays in mediating male–male cooperation and mate harm. If within-group male relatedness is mediating sexual conflict in this system, brothers should cause less harm than unrelated males resulting in higher relative fitness of females

Methods

Results

Discussion