| Popis: |
Personality in animals describes a suite of correlated behavioural traits that distinguishes one individual from another. One important personality measure is boldness, which is related to intraspecific differences in responses to novelty, levels of activity and aggressiveness, propensity for exploration, and capacity for learning and memory. Personality and boldness have previously been linked with physiological responses to stress, termed coping styles, wherein lower stress responsiveness often correlates with bolder behaviour. Variation in these traits has important implications for how animals respond to environmental challenges. Personality and stress responsiveness are both also partly heritable; a greater understanding of the genetic control of behavioural and physiological traits is therefore necessary to understand how individual differences are maintained in the face of natural selection, and how genes can control changes in behaviour and physiology. Boldness and behavioural plasticity was therefore examined in the rainbow trout, Oncorhynchus mykiss Walbaum, which provides an excellent model since the behaviour and physiology of this economically important species has been well-studied. Throughout, boldness was assessed using novel object tests, where latency to approach to within 5 cm of an object was the primary determinant. Trout which approached within 180 s were considered bold, those which did not approach within 300 s as shy, and the remainder as intermediate which were discarded from analysis. Boldness was consistent over time in two lines of rainbow trout bred for a divergent response to stress, but no correlation was found between boldness and either stress responsiveness or gene expression, in contrast to expectations. Stress responsiveness was, however, strongly linked with gene expression: a suite of candidate genes was uniformly upregulated in low stress-responding trout compared to high-responders, suggesting fine control of hormones and receptors throughout the stress response may occur downstream of gene expression. Outbred bold rainbow trout placed into a group of either completely bold or completely shy trout tended to become shyer, whereas initially shy trout did not display any behavioural plasticity. Likewise, bold trout exposed to predation threat in combination with different levels of feed availability modified 'their behaviour seemingly dependent upon the combination of risk level and internal state. Shy trout, again, were less labile. This is in contrast to coping style theory which suggests shy, reactive animals have more behavioural flexibility than bold, proactive individuals. When exposed to variable abiotic factors - increased temperature and reduced dissolved oxygen content - both bold and shy fish exhibited some behavioural change dependent upon the combination of factors. When exposed to these stressors and challenges, plasma cortisol levels more closely matched behavioural profiles such that shy trout generally had a greater stress response than bold trout, and this could be linked to exposure to threat or temperature change. Furthermore, gene expression profiles corresponded with predation threat: genes coding for corticotrophin releasing factor (CRF), ependymin and y-aminobutyric acid A (GABAA) increased in expression under increasing threat levels, indicating these genes were involved in the response to this particular challenge. These results thus show the existence of personality in rainbow trout, linking responses towards novelty with levels of activity and identifying physiological and genetic correlates to these behavioural traits. Boldness was shown not to be a fixed trait but, instead, dependent upon social, environmental, nutritional and energetic state and on intensity of risk. Bold trout generally altered their behavioural strategy in an adaptive manner according to both context and state yet shy individuals remained shy. These empirical data highlight the importance of taking individual personality into account when assessing molecular, physiological and behavioural responses to stimuli. Furthermore, these data provide new insights into intraspecific variation within a variety of contexts that may be used to fuel theoretical models of the evolutionary and ecological significance of animal personalities. |
