In the past decade, several conceptual papers have linked variation in animal personality to variation in cognition, and recent years have seen a flood of empirical studies testing this link. However, these results have not been synthesized in a quantitative way. Here, we systematically search the literature and conduct a phylogenetically controlled meta-analysis of empirical papers that have tested the relationship between animal personality (exploration, boldness, activity, aggression and sociability) and cognition (initial learning/reversal speed, number of correct choices/errors after standard training). We find evidence for a small but significant relationship between variation in personality and variation in learning across species in the absolute scale; however, the of this relationship is highly variable and when both positive and negative effect sizes are considered, the average effect size does not differ significantly from zero. Importantly, this variation among studies is not explained by differences in personality or learning measure, or taxonomic grouping. Further, these results do not support current hypotheses suggesting that that fast-explorers are fast-learners or that slow-explorers perform better on tests of reversal learning. Rather, we find evidence that bold animals are faster learners, but only when boldness is measured in response to a predator (or simulated predator) and not when boldness is measured by exposure to a novel object (or novel food). Further, although only a small sub-sample of papers reported results separately for males and females, sex explained a significant amount of variation in effect size. These results, therefore, suggest that, while personality and learning are indeed related across a range of species, the direction of this relationship is highly variable. Thus further empirical work is needed to determine whether there are important moderators of this relationship.This article is part of the theme issue 'Causes and consequences of individual differences in cognitive abilities'.

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Traumatic mating (or copulatory wounding) is an extreme form of sexual conflict whereby male genitalia physically harm females during mating. In such species females are expected to evolve counter-adaptations to reduce male-induced harm. Importantly, female counter-adaptations may include both genital and non-genital traits. In this study, we examine evolutionary associations between harmful male genital morphology and female reproductive tract morphology and immune function across 13 populations of the seed beetle We detected positive correlated evolution between the injuriousness of male genitalia and putative female resistance adaptations across populations. Moreover, we found evidence for a negative relationship between female immunity and population productivity, which suggests that investment in female resistance may be costly due to the resource trade-offs that are predicted between immunity and reproduction. Finally, the degree of female tract scarring (harm to females) was greater in those populations with both longer aedeagal spines and a thinner female tract lining. Our results are thus consistent with a sexual arms race, which is only apparent when both male and female traits are taken into account. Importantly, our study provides rare evidence for sexually antagonistic coevolution of male and female traits at the within-species level.

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Animals often need to signal to attract mates, and sexual signalling may impose significant energetic and fitness costs to signallers. Consequently, individuals should strategically adjust signalling effort in order to maximise the fitness payoffs of signalling. An important determinant of these payoffs is individual state, which can influence the resources available to signallers, the likelihood of mating, and the motivation to mate. However, empirical studies often find contradictory patterns of state-based signalling. For example, some studies find that individuals in poor condition signal less, in order to conserve resources (ability-based signalling). In other cases, individuals in poor condition signal more, in order to maximise short-term reproductive success (needs-based signalling). I used meta-analysis to examine animal sexual signalling behaviour in relation to six aspects of individual state: age, mated status, attractiveness, body size, condition, and parasite load. Across 228 studies and 147 species, individuals (who were overwhelmingly male) signalled significantly more when in good condition, and there was a strong positive trend for increased signalling for large, attractive individuals with a low parasite load. Overall, this suggests that animal sexual signalling behaviour is generally honest and ability-based. However, needs-based signalling (terminal investment) was found when considering age, with old virgins signalling more than young virgins. Sexual signalling was not significantly influenced by mated status. There was a large amount of heterogeneity across studies that remained unexplained, and therefore more work is needed to determine the ecological factors influencing the magnitude and direction of state-dependent sexual signalling..