Data from: Within-group male relatedness reduces harm to females in Drosophila

To resolve the mechanisms that switch competition to cooperation is key to understanding biological organization. This is particularly relevant for intrasexual competition, which often leads to males harming females. Recent theory proposes that kin selection may modulate female harm by relaxing competition among male relatives. Here we experimentally manipulate the relatedness of groups of male Drosophila melanogaster competing over females to demonstrate that, as expected, within-group relatedness inhibits male competition and female harm. Females exposed to groups of three brothers unrelated to the female had higher lifetime reproductive success and slower reproductive ageing compared to females exposed to groups of three males unrelated to each other. Triplets of brothers also fought less with each other, courted females less intensively and lived longer than triplets of unrelated males. However, associations among brothers may be vulnerable to invasion by minorities of unrelated males: when two brothers were matched with an unrelated male, the unrelated male sired on average twice as many offspring as either brother. These results demonstrate that relatedness can profoundly affect fitness through its modulation of intrasexual competition, as flies plastically adjust sexual behaviour in a manner consistent with kin-selection theory.阐明将竞争转化为合作的内在机制，是解析生物组织逻辑的核心所在。这一点对于性内竞争（intrasexual competition）尤为关键，而这类竞争往往会致使雄性对雌性造成伤害。近期有理论提出，亲缘选择（kin selection）可通过缓解雄性亲属间的竞争，来调控雄性对雌性的伤害行为。本研究通过实验操控争夺雌性的黑腹果蝇（Drosophila melanogaster）雄性群体的亲缘关系，证实正如预期那般，群体内的亲缘关系能够抑制雄性间的竞争以及对雌性的伤害行为。相较于暴露于3只无亲缘关系雄性群体的雌性果蝇，暴露于3只同胞兄弟雄性群体的雌性果蝇，其终身繁殖成功率更高，生殖衰老速度也更为缓慢。与无亲缘关系的雄性三胞胎组相比，同胞兄弟三胞胎组的雄性之间争斗频次更低，对雌性的求偶行为强度更弱，且寿命更长。但同胞兄弟间的群体关联或许极易受到少量无亲缘关系雄性的入侵：当2只同胞兄弟与1只无亲缘关系雄性共处时，该无亲缘关系雄性的平均后代数量是任一同胞兄弟的两倍。上述研究结果表明，亲缘关系可通过调控性内竞争，对果蝇的适合度（fitness）产生深远影响——果蝇会以契合亲缘选择理论的方式，对自身的性行为进行可塑性调节。