) and, because selection for one particular behaviour usually co-selects for other traits, either behavioural or morphological, uncover gene epistatic and pleiotropic effects. Studying organisms that have been under strong artificial selection for particular behavioural traits may facilitate the identification of genetic and physiological mechanisms underlying the expression of that behaviour (e.g. The comparison between domesticated and wild-type strains was key to Darwin’s theory of natural selection and since then it has enriched our understanding of the general mechanisms of behaviour and its evolutionary principles. Domestication is a particularly interesting example as it usually combines adaptation to captive conditions and selective breeding for particular traits. These manipulations may be carried out under controlled conditions in laboratory or natural settings or arise from unintended natural experiments. splendens.Īrtificial selection and experimental evolution are powerful tools for testing proximate and ultimate causes of behaviour. These results suggest that selection for male winners co-selected for high-frequency and metabolic demanding aggressive display in males and also enhanced female aggression, opening a wide range of testable hypothesis about the ultimate and proximate mechanisms of male and female aggression in B. The study further shows that results were largely independent of the stimulus type, with the mirror test inducing similar and less variable responses than the live conspecific presentation. Aggressive behaviours were correlated across male and female fighter siblings, suggesting common genetic and physiological mechanisms to male and female aggression in this species. Females of the fighter strain, which are not used for fights, were also more aggressive than wild-type females. Wild-type males were less active and exhibited aggressive displays mostly in close proximity to the stimuli. Fighter males had an overall higher swimming activity, performing frequent fast strikes in the direction of the intruder and displaying from a distance. Differences were not only quantitative but the pattern of fight display was also divergent. Fighter males were more aggressive than wild-type males for all measured behaviours. The aggressive response of adult fish was tested against their mirror image or a size-matched conspecific. We assessed the results of this long-term selection process by comparing under standard laboratory conditions male and female aggressive behaviour of one strain selected for staged fights (“fighters”) and one strain of wild-types. Breeders discard losing batches and reproduce winner batches with the aim of increasing fight performance. During the selection process, matched for size males fight in a small tank until the contest is resolved. In Southeast Asia, males of the Siamese fighting fish Betta splendens have been selected across centuries for paired-staged fights.
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