The notion that men are more variable than women has become embedded into scientific thinking. For mental traits like personality, greater male variability has been partly attributed to biology, underpinned by claims that there is generally greater variation among males than females in non‐human animals due to stronger sexual selection on males. However, evidence for greater male variability is limited to morphological traits, and there is little information regarding sex differences in personality‐like behaviours for non‐human animals. Here, we meta‐analysed sex differences in means and variances for over 2100 effects (204 studies) from 220 species (covering five broad taxonomic groups) across five personality traits: boldness, aggression, activity, sociality and exploration. We also tested if sexual size dimorphism, a proxy for sex‐specific sexual selection, explains variation in the magnitude of sex differences in personality. We found no significant differences in personality between the sexes. In addition, sexual size dimorphism did not explain variation in the magnitude of the observed sex differences in the mean or variance in personality for any taxonomic group. In sum, we find no evidence for widespread sex differences in variability in non‐human animal personality.

Winning or losing a fight can have lasting effects on competitors. Controlling for inherent fighting ability and other factors, a history of winning often makes individuals more likely to win future contests, while the opposite is true for losers (the 'winner-loser effect'). But does the winner-loser effect also influence a male's mating success? We experimentally staged contests between male mosquitofish () such that focal males either won or lost three successive encounters with stimulus males. We then placed a size-matched (to control for inherent fighting ability) winner and loser with a female and monitored their behaviour ( = 63 trios). Winners spent significantly more time associating with the female. Winners did not make more copulation attempts, nor have a greater number of successful attempts. There was, however, a significant effect of male size on the number of successful copulation attempts: success decreased with male size for losers, but size had no effect on the success rate of winners.

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.

The environmental conditions that an individual experiences during its development and early life can have a lasting effect on its adult traits and performance. Abiotic factors, such as nutrition or humidity, and biotic factors, such as competition or predation risk, experienced during key periods of development are often key in determining the development of life-history traits (e.g. Metcalfe & Monaghan, 2001; Relyea, 2001). How individuals respond to their environment during development is evolutionarily important because it can influence how they interact with their environment as adults, hence their relative fitness. In general, most responses to early life environments are either adaptive or nonadaptive. Adaptive responses increase an individual's fitness because they

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