There is increasing interest in individual differences in animal behaviour. Recent research now suggests that an individual’s behaviour, once considered to be plastic, may be more predictable than previously thought. Here, we take advantage of the large number of studies that have estimated the repeatability of various behaviours to evaluate whether there is good evidence for consistent individual differences in behaviour and to answer some outstanding questions about possible factors that can influence repeatability. Specifically, we use meta-analysis to ask whether different types of behaviours were more repeatable than others, and if repeatability estimates depended on taxa, sex, age, field versus laboratory, the number of measures and the interval between measures. Some of the overall patterns that were revealed by this analysis were that repeatability estimates were higher in the field compared to the laboratory and repeatability was higher when the interval between observations was short. Mate preference behaviour was one of the best studied but least repeatable behaviours. Our findings prompt new insights into the relative flexibility of different types of behaviour and offer suggestions for the design and analysis of future research.

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Predation pressure represents a strong selective force that influences the development and evolution of living organisms. An increasing number of studies have shown that both environmental and social factors, including exposure to predators, substantially shape the structure and function of the brain. However, our knowledge about the molecular mechanisms underlying the response of the brain to environmental stimuli is limited. In this study, we used whole-genome comparative oligonucleotide microarrays to investigate the brain transcriptomic response to cues of a predator in the threespine stickleback, Gasterosteus aculeatus. We found that repeated exposure to olfactory, visual and tactile cues of a predator (rainbow trout, Oncorrhynchus mykiss) for 6 days resulted in subtle but significant transcriptomic changes in the brain of sticklebacks. Gene functional analysis and gene ontology enrichment revealed that the majority of the transcripts differentially expressed between the fish exposed to cues of a predator and the control group were related to antigen processing and presentation involving the major histocompatibility complex, transmission of synaptic signals, brain metabolic processes, gene regulation and visual perception. The top four identified pathways were synaptic long-term depression, RAN signaling, relaxin signaling and phototransduction. Our study demonstrates that exposure of sticklebacks to cues of a predator results in the activation of a wide range of biological and molecular processes and lays the foundation for future investigations on the molecular factors that modulate the function and evolution of the brain in response to stressors.

This study examined the patterns of morphological variation both between species, and between sexes and among populations within each species of the Mexican sailfin mollies, Poecilia velifera and Poecilia petenensis, using geometric morphometrics and linear measurements of morphological traits. While sexes within each species differed in characteristics that may be important in sexual selection, such as length of the dorsal fin, species differed in traits, such as body depth, that may also be influenced by natural selection due to differences in habitats. Within each species, many morphological traits were similar among populations, but important differences, including caudal peduncle depth in P. petenensis (but not in P. velifera), suggested that habitat differences may also be important in shaping population divergence independently within each species. Indeed, the evolutionary vectors of male morphological population divergence for each species differed by an angle of 98Á5 , representing nearly orthogonal vectors and suggesting independent shape divergence between these two molly species. Finally, geographic isolation did not explain the morphological differentiation seen among populations, suggesting that natural and sexual selection were strong forces promoting morphological diversification within these two species, despite the potential for a high degree of population connectivity and gene flow.

Predation has an important influence on life history traits in many organisms, especially when they are young. When cues of trout were present, juvenile sticklebacks grew faster. The increase in body size as a result of exposure to cues of predators was adaptive because larger individuals were more likely to survive predation. However, sticklebacks that had been exposed to cues of predators were smaller at adulthood. This result is consistent with some life history theory. However, these results prompt an alternative hypothesis, which is that the decreased size at adulthood reflects a deferred cost of early rapid growth. Compared to males, females were more likely to survive predation, but female size at adulthood was more affected by cues of predators than male size at adulthood, suggesting that size at adulthood might be more important to male fitness than to female fitness.