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Thursday, July 9, 2015

Sex differences in senescence: the role of intra-sexual competition in early adulthood

Christopher Beirne, Richard Delahay, Andrew Young
Males and females frequently differ in their rates of ageing, but the origins of these differences are poorly understood. Sex differences in senescence have been hypothesized to arise, because investment in intra-sexual reproductive competition entails costs to somatic maintenance, leaving the sex that experiences stronger reproductive competition showing higher rates of senescence. However, evidence that sex differences in senescence are attributable to downstream effects of the intensity of intra-sexual reproductive competition experienced during the lifetime remains elusive. Here, we show using a 35 year study of wild European badgers (Meles meles), that (i) males show higher body mass senescence rates than females and (ii) this sex difference is largely attributable to sex-specific downstream effects of the intensity of intra-sexual competition experienced during early adulthood. Our findings provide rare support for the view that somatic maintenance costs arising from intra-sexual competition can cause both individual variation and sex differences in senescence.
Author Christopher Beirne from the Centre for Ecology and Conservation at the University of Exeter's Penryn Campus in Cornwall said: "The study shows that when male badgers don't have to fight for a mate, they can prioritise their health and wellbeing and as a result they age more slowly. However, when badgers fight a lot in their youth, they really pay for it by ageing rapidly in later life."
Unlike the males, female badgers appeared to be unaffected by the density of other females in the area, indicating that they don't suffer from the effects of competition in the same way as males.
Co-author Dr Andrew Young from the University of Exeter said: "The findings are particularly interesting because males age faster than females in many species, including our own, but we don't really understand why. Our findings suggest that malebadgers age faster than females because of the male-male competition that they experience during their lifetimes; males that experience strong competition age more quickly than females, while males that experience little competition do not."

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