Disentangling the effects of male-male competition, reproductive investment and social dominance on telomere length

Energetically costly events can accelerate telomere loss and ageing via oxidative damage. For adult males, increased levels of reproduction and more frequent fighting for access to mates are therefore stressful experiences that should hasten telomere shortening. Testing for these relationships is, however, confounded by potential correlations between social status and reproductive investment. We used a 2 x 2 experimental design to test how long-term winning or losing contests, in combination with variation in reproductive effort, influenced telomere loss and several key life-history traits in the eastern mosquitofish, Gambusia holbrooki. After 9 weeks there were significant differences between winners and losers in their pre-copulatory reproductive investment (i.e., mating effort), but not in their post-copulatory reproductive investment (i.e., ejaculates). Males that were previously able to mate with females (i.e., had greater past reproductive investment) had significantly lower current mating effort, lower body growth, and slower swimming sperm, but only when males were small. These findings suggest that mating costs incurred from both consistent contest experiences and past reproductive effort depend on male body size. Finally, males that had previously been able to mate with a female did not have shorter telomeres than males that were unable to mate, while there was equivocal evidence that winners had shorter telomeres than losers. This intriguing finding hints at the important role social dynamics play in determining relative male investment into reproduction and somatic maintenance.