Male relatedness and familiarity are required to modulate male-induced harm to females in Drosophila
Sally Le page1, Irem Sepil1, Ewan Flintham1, Tommaso Pizzari1, Pau Carazo2 and Stuart Wigby1
1Edward Grey Institute, Department of Zoology, University of Oxford, Oxford, UK
2Behaviour, Ecology and Evolution group, Instituto Cavanilles of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain
SLP, 0000-0003-3300-1344; PC, 0000-0002-1525-6522; SW, 0000-0002-2260-2948
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.
Introduction
The evolutionary strategies that maximize female fitness may simultaneously hamper male fitness and vice versa, generating sexual conflict over reproductive decisions [1–3]. This conflict often arises because intense competition among males over access to mating and fertilization opportunities can harm females (i.e. reduce their fitness). Such harm has been likened to a tragedy of the commons [4–7], in which selfish exploitation results in the depletion, or even destruction, of a shared resource. Male harm of females may occur through a number of pathways including sexual harassment, sexual coercion, traumatic insemination, male accessory gland products, pathological polyspermy and infanticide [2]. In all these cases, sexual selection promotes male strategies even if they happen to harm females in the process (i.e. collateral female harm), or precisely because they harm females (e.g. [8]). Male harm of females is emerging as an important factor in population ecology and evolution, as increasing evidence indicates its role in a number of fundamental processes, such as dispersal [9], population extinction [10] and intersexual coevolution [2]. However, the mechanisms underpinning the variation in the severity of female harm observed across species and populations remain little understood.
Recent theoretical work has suggested that indirect fitness effects might play a key role in modulating male harm to females [6,11–14]. This happens
