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The outcome of sexual conflict can depend on the social environment, as males respond to changes in the inclusive fitness payoffs of harmfulness and harm females less when they compete with familiar relatives. Theoretical models also predict that if limited male dispersal predictably enhances local relatedness while maintaining global competition, kin selection can produce evolutionary divergences in male harmfulness among populations. Experimental tests of these predictions, however, are rare. We assessed rates of dispersal in female and male seed beetles Callosobruchus maculatus, a model species for studies of sexual conflict, in an experimental setting. Females dispersed significantly more often than males, but dispersing males travelled just as far as dispersing females. Next, we used experimental evolution to test whether limiting dispersal allowed the action of kin selection to affect divergence in male harmfulness and female resistance. Populations of C. maculatus were evolved for 20 and 25 generations under one of three dispersal regimens: completely free dispersal, limited dispersal and no dispersal. There was no divergence among treatments in female reproductive tract scarring, ejaculate size, mating behaviour, fitness of experimental females mated to stock males or fitness of stock females mated to experimental males. We suggest that this is likely due to insufficient strength of kin selection rather than a lack of genetic variation or time for selection. Limited dispersal alone is therefore not sufficient for kin selection to reduce male harmfulness in this species, consistent with general predictions that limited dispersal will only allow kin selection if local relatedness is independent of the intensity of competition among kin. [ABSTRACT FROM AUTHOR]

Males of many species harm females as a byproduct of intrasexual competition, but this harm can be reduced if males are less competitive in the presence of familiar relatives. We determined the cue males use to identify competitors in this context. We assessed genetic variance in a putative kin recognition trait (cuticular hydrocarbons) in male seed beetles Callosobruchus maculatus and found that five hydrocarbons had significant components of additive genetic variance and could serve as relatedness cues. Next, we tested whether hydrocarbons were the mechanism males use to distinguish the social identities of competitors when strategically adjusting their competitiveness/harmfulness. Pairs of female and male C. maculatus were mated in the presence of hydrocarbons extracted from males that differed in their relatedness and familiarity to the focal male. Females were more productive after mating in the presence of extracts from the focal male's nonrelatives, if those extracts were also unfamiliar to the focal male. Relatedness had no effect on productivity when extracts were familiar to the focal male. These results may be reconciled with those of previous studies that manipulated the relatedness and familiarity of competing males if the difference between the effect of harmfulness on productivity following a single mating and the effect on lifetime reproductive fitness after multiple matings is accounted for. This study provides a novel demonstration of the mechanism of social recognition in the moderation of sexual conflict. [ABSTRACT FROM AUTHOR]

Males of many species adjust their reproductive investment to the number of rivals present simultaneously. However, few studies have investigated whether males sum previous encounters with rivals, and the total level of competition has never been explicitly separated from social familiarity. Social familiarity can be an important component of kin recognition and has been suggested as a cue that males use to avoid harming females when competing with relatives. Previous work has succeeded in independently manipulating social familiarity and relatedness among rivals, but experimental manipulations of familiarity are confounded with manipulations of the total number of rivals that males encounter. Using the seed beetle Callosobruchus maculatus, we manipulated three factors: familiarity among rival males, the maximum number of rivals encountered simultaneously and the total number of rivals encountered over a 48 h period. Males produced smaller ejaculates when exposed to more rivals in total, regardless of the maximum number of rivals they encountered simultaneously. Males did not respond to familiarity. Our results demonstrate that males of this species can sum the number of rivals encountered over separate days, and therefore the confounding of familiarity with the total level of competition in previous studies should not be ignored. [ABSTRACT FROM AUTHOR]

Sexual conflict occurs when reproductive partners have different fitness optima, and can lead to the evolution of traits in one sex that inflict fitness costs on the opposite sex. Recently, it has been proposed that antagonism by males towards females should be reduced when they compete with relatives, because reducing the future productivity of a female would result in an indirect fitness cost for a harmful male. We tested this prediction in the seed beetle Callosobruchus maculatus, the males of which harm females with genital spines and pre-copulatory harassment. We compared lifespan, lifetime egg production and lifetime offspring production among females housed with groups of males that varied in their familiarity and relatedness. Females produced significantly more eggs and offspring when grouped with males who were both related and familiar to each other. Therewas no effect of male relatedness or familiarity on female lifespan. Our results suggest that males plastically adjust their harmfulness towards females in response to changes in inclusive fitness payoffs, and that in this species both genetic relatedness and social familiarity mediate this effect. [ABSTRACT FROM AUTHOR]