Within-group male relatedness reduces harm to females in Drosophila

• Published in: Nature (London) 2014-01, Vol.505 (7485), p.672-675
• Main Authors: Carazo, Pau, Tan, Cedric K. W., Allen, Felicity, Wigby, Stuart, Pizzari, Tommaso
• Format: Article
• Language: English
• Subjects: 631/181/2469; 64; 64/24; Aging; Animal behavior; Animal reproduction; Animals; Biological research; Biology, Experimental; Competition; Competitive Behavior - physiology; Cooperative Behavior; Courtship of animals; Drosophila; Drosophila melanogaster - genetics; Drosophila melanogaster - physiology; Experiments; Female; Females; Heredity - physiology; Humanities and Social Sciences; Insects; letter; Longevity - genetics; Longevity - physiology; Male; Males; Models, Biological; multidisciplinary; Natural selection; Offspring; Principal components analysis; Reproduction; Reproduction - physiology; Science; Sexual behavior; Sexual Behavior, Animal - physiology; Siblings; Studies; Survival analysis
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature12949

Relatedness can affect fitness through modulation of intrasexual competition in Drosophila melanogaster ; male competition and female harm are lower when three related males compete over an unrelated female than when three unrelated males compete, but when two brothers and an unrelated male compete, the unrelated male sires twice as many offspring as either brother, suggesting that minorities of unrelated competitors may be able to infiltrate coalitions of relatives. Keeping male competition in the family Recent theory suggests that competition between males, a possible cause of harm to females, can be moderated by cooperation between males due to relatedness between them. These authors demonstrate that this is true experimentally by manipulating the relatedness of Drosophila males. Females mated with groups of brothers have greater lifetime reproductive fitness and slower reproductive ageing than those mated with groups of unrelated males. Within the male groups, aggressive behaviour is reduced between brothers, but brothers paired with an unrelated male have reduced reproductive success. To resolve the mechanisms that switch competition to cooperation is key to understanding biological organization 1 . This is particularly relevant for intrasexual competition, which often leads to males harming females 2 . Recent theory proposes that kin selection may modulate female harm by relaxing competition among male relatives 3 , 4 , 5 . 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.