The Effect of Brief or Prolonged Bouts of Winning or Losing Male-Male Contests on Plasticity in Sexually Selected Traits

Abstract

Fight outcomes often affect male fitness by determining their access to mates. Thus 'winnerloser' effects, where winners often win their next contest, while losers tend to lose, can influence how males allocate resources towards pre-and post-copulatory traits. We experimentally manipulated the winning/losing experiences of pairs of size-matched male Gambusia holbrooki for either a day, a week or three weeks to test whether prior winning/losing experiences differentially affect the plasticity of male investment into either mating effort (pre-copulatory) or ejaculates (post-copulatory). When winner/loser pairs directly competed for a female, winners had better pre-copulatory outcomes than losers for three of the four traits we measured: mating attempts, successful attempts, and time spent with the female (but not aggression). However, winners and losers did not differ in either their total sperm counts nor sperm velocity.Interestingly, absolute male size, an important predictor of fighting success, mediated winnerloser effects on how long males then spent near a female. Compared to losers, smaller winners spent more time with the female than did larger winners, suggesting that how males respond to prior social experiences is size-dependent. We discuss the general importance of controlling for inherent male condition when comparing male investment into condition-dependent traits.

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

“…We investigated how long-term winning or losing, in combination with variation in reproductive effort, influences telomere length and life-history strategies in male eastern mosquitofish, Gambusia holbrooki. This promiscuous poecilid species has been used previously as a model organism to study winner-loser effects on male reproduction (Harrison et al 2018(Harrison et al , 2023. Males engage in agonistic interactions to establish dominance hierarchies (Harrison et al 2018(Harrison et al , 2023, and otherwise spend most of their time pursuing and attempting to 'sneak' copulate with females (Bisazza and Marin 1991;McPeek 1992).…”

“…This promiscuous poecilid species has been used previously as a model organism to study winner-loser effects on male reproduction (Harrison et al 2018(Harrison et al , 2023. Males engage in agonistic interactions to establish dominance hierarchies (Harrison et al 2018(Harrison et al , 2023, and otherwise spend most of their time pursuing and attempting to 'sneak' copulate with females (Bisazza and Marin 1991;McPeek 1992). Males invest heavily into both competition and reproduction, and they tend to survive for only one breeding season (Kahn et al 2013).…”

“…As such, male mosquitofish likely tradeoff reproductive investment and lifespan. Based on earlier work (Harrison et al 2023) we expected that consistently winning or losing contests, and body size, will combine to mediate trade-offs between reproduction and telomere length/lifespan.…”

“…While the outcome of a single contest is unlikely to shorten telomeres, a consistent imbalance of cortisol and testosterone following a history of consistently either winning or losing contests could exacerbate oxidative damage and accelerate telomeric attrition (Casagrande and Hau 2019). Males that consistently win contests might adaptively increase their allocation of investment into reproductive rather than somatic traits to take advantage of their winning status (Harrison et al 2023). We already know that prior contest experience can influence male reproduction.…”

“…For instance, after only a single contest between size-matched male fruit flies, winners are more likely to mate with females while losers are more effective at sperm competition (Filice and Dukas 2019). Similarly, winning male mosquitofish spend more time than losers with females (Harrison et al 2018); and after a consistent, long-term experience of winning or losing contests, winning male mosquitofish have better pre-copulatory outcomes than losers (Harrison et al 2023). These differences in the reproductive investment of winners and losers are likely to trade-off with other life-history traits, such as somatic maintenance, and even lifespan, as males attempt to maximise their relative fitness (Kirkwood and Rose 1991).…”