Abstract
Males compete over mating and fertilization, and often harm females in the process. Inclusive fitness theory predicts that increasing relatedness within groups of males may relax competition and discourage male harm of females as males gain indirect benefits. Recent studies in Drosophila melanogaster are consistent with these predictions, and have found that within-group male relatedness increases female fitness, though others have found no effects. Importantly, these studies did not fully disentangle male genetic relatedness from larval familiarity, so the extent to which modulation of harm to females is explained by male familiarity remains unclear. Here we performed a fully factorial design, isolating the effects of male relatedness and larval familiarity on female harm. While we found no differences in male courtship or aggression, there was a significant interaction between male genetic relatedness and familiarity on female reproduction and survival. Relatedness among males increased female lifespan, reproductive lifespan and overall reproductive success, but only when males were familiar. By showing that both male relatedness and larval familiarity are required to modulate female harm, these findings reconcile previous studies, shedding light on the potential role of indirect fitness effects on sexual conflict and the mechanisms underpinning kin recognition in fly populations.
Highlights
The evolutionary strategies that maximize female fitness may simultaneously hamper male fitness and vice versa, generating sexual conflict over reproductive decisions [1,2,3]
While we found no effect on male behaviours, we did observe an interaction between male relatedness and larval familiarity, thereby showing that larval familiarity alone is insufficient to reduce harm to females
The use of a fully factorial design enables the present study to show that both genetic relatedness and familiarity during development are required for any modulation of male harm to females in our population of D. melanogaster
Summary
The evolutionary strategies that maximize female fitness may simultaneously hamper male fitness and vice versa, generating sexual conflict over reproductive decisions [1,2,3]. Carazo et al [22] found that females had higher lifetime reproductive success and slower reproductive ageing (a more gradual decline in fecundity and fertility with age) when exposed to a triplet of brothers that were unrelated to the female but had been raised together as larvae than when exposed to a triplet of males that were unrelated to each other and had been raised separately as larvae These patterns have been explored by different research groups and in different D. melanogaster populations [23 –26] resulting in some studies reporting results consistent with Carazo et al.’s findings and others reporting no effects (summarized in electronic supplementary material, table S1), suggesting that these effects are not entirely consistent and that they might be modulated by other mechanisms. Male relatedness increased female reproductive success, lifespan and reproductive lifespan, and slowed reproductive ageing, but only when males were familiar
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