Winner-loser effects on life history traits

Abstract

Ageing of adult males could be accelerated by both high mating/reproductive effort and fighting for mates. Testing the relative importance of these factors is challenging, however, because males that win fights also tend to have more mates. We used a 2 × 2 experimental design to test how a prolonged (9 week) period of either winning or losing fights, and either high or low reproductive effort (manipulating by varying access to females) interacts to affect male ageing and future reproduction allocation in the mosquitofish, Gambusia holbrooki. We measured telomere length and several life-history traits, including mating effort and ejaculates (sperm count and velocity). After 9 weeks, there were significant differences between winners and losers in their mating effort but not in their ejaculates. Males with a higher past reproductive effort (i.e., access to females) had significantly lower current mating effort and grew more slowly. Males with a higher past reproductive effort also had slower swimming sperm, but only if they were smaller than average in body size. Surprisingly, neither males with a higher past reproductive effort nor males that repeatedly lost fights had shorter telomeres. Our findings show that past social dynamics affect how males allocate resources to reproduction and somatic maintenance.

Keywords: ageing; male–male competition; mating costs; mosquitofish; oxidative stress; telomeres.