In Southeast Asia, males of the Siamese fighting fish Betta splendens have been selected across centuries for paired-staged fights. During the selection process, matched for size males fight in a small tank until the contest is resolved. Breeders discard losing batches and reproduce winner batches with the aim of increasing fight performance. 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. The aggressive response of adult fish was tested against their mirror image or a size-matched conspecific. Fighter males were more aggressive than wild-type males for all measured behaviours. Differences were not only quantitative but the pattern of fight display was also divergent. Fighter males had an overall higher swimming activity, performing frequent fast strikes in the direction of the intruder and displaying from a distance. Wild-type males were less active and exhibited aggressive displays mostly in close proximity to the stimuli. Females of the fighter strain, which are not used for fights, were also more aggressive than wild-type females. Aggressive behaviours were correlated across male and female fighter siblings, suggesting common genetic and physiological mechanisms to male and female aggression in this species. 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. 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. splendens.

中文翻译：

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暹罗斗鱼 Betta splendens 中雄性获胜者的人工选择与雌性的高攻击性相关

在东南亚，几个世纪以来，暹罗斗鱼 Betta splendens 的雄性都被选来进行配对战斗。在选择过程中，体型相匹配的雄性在小水箱中进行战斗，直到比赛结束。育种者丢弃失败的批次并繁殖获胜的批次，目的是提高战斗性能。我们通过在标准实验室条件下比较选择用于分阶段战斗的一种品系（“战士”）和一种野生型品系的雄性和雌性攻击行为，评估了这一长期选择过程的结果。成年鱼的攻击性反应是根据它们的镜像或大小匹配的同种鱼进行测试的。在所有测量的行为中，雄性斗士都比野生型雄性更具攻击性。差异不仅是数量上的差异，而且战斗展示的方式也有所不同。雄性斗士的游泳活动总体较高，经常向入侵者的方向进行快速攻击，并从远处进行展示。野生型雄性不太活跃，并且大多在靠近刺激物时表现出攻击性。不用于战斗的斗士品系的雌性也比野生型雌性更具攻击性。男性和女性战斗机兄弟姐妹的攻击行为是相关的，这表明该物种的男性和女性攻击行为具有共同的遗传和生理机制。该研究进一步表明，结果在很大程度上与刺激类型无关，镜子测试与现场同种演示相比，会产生相似且变化较小的反应。这些结果表明，对雄性获胜者的选择共同选择了雄性的高频和代谢要求的攻击性表现，同时也增强了雌性的攻击性，为芨芨草中雄性和雌性攻击性的最终和近似机制提供了广泛的可检验的假设。