Predictability is attractive: Female preference for behaviourally consistent males but no preference for the level of male aggression in a bi-parental cichlid

Although personality traits can largely affect individual fitness we know little about the evolutionary forces generating and maintaining personality variation. Here, we investigated the hypothesis that personality variation in aggression is sexually selected in the monogamous, bi-parental cichlid Pelvicachromis pulcher. In this species, breeding pairs form territories and they aggressively defend their territory and offspring against con- and heterospecific intruders. In our mate choice study, we followed up two alternative hypotheses. We either expected females to show a directional preference for a high level and high consistency of aggression (potentially indicating mate choice for male parental quality). Alternatively, we expected females to choose males for (dis-)similarity in the level/consistency of aggression (potentially indicating mate choice for compatibility). Individual level and consistency of aggression were assessed for males and females using mirror tests. After eavesdropping on aggressive behaviour of two males (differing in level and consistency of aggression) females were then allowed to choose between the two males. Males, but not females, showed personality variation in aggression. Further, females generally preferred consistent over inconsistent males independent of their level of aggression. We did not detect a general preference for the level of male aggression. However, we found an above average preference for consistent high-aggression males; whereas female preference for inconsistent high-aggression did not deviate from random choice. Our results suggest behavioural consistency of aggression in male rainbow kribs is selected for via female mate choice. Further, our study underlines the importance of considering both the level and the consistency of a behavioural trait in studies of animal behaviour.尽管人格特质可在很大程度上影响个体适应度（fitness），但目前学界对驱动并维持人格变异的进化力量仍知之甚少。本研究以实行单配偶制的双亲抚育型慈鲷——彩虹短鲷（Pelvicachromis pulcher）为研究对象，验证了“攻击性的人格变异可通过性选择得以塑造与维持”这一假说。该物种的繁殖配对个体将划定专属领地，并会主动抵御同种（conspecific）及异种（heterospecific）入侵者，以保卫自身领地与后代。在本次配偶选择研究中，我们设置了两组对立待验假说：其一，我们推测雌性可能会对攻击性水平高且攻击性一致性强的雄性表现出定向偏好（这可能反映了雌性对雄性抚育质量的择偶选择）；其二，我们推测雌性可能会依据雄性在攻击性水平/一致性上的（不）相似性来选择配偶（这可能反映了雌性对相容性的择偶选择）。研究人员通过镜像测试（mirror test）来评估雌雄个体的攻击性水平与攻击性一致性。在让雌性旁观两只攻击性水平与一致性存在差异的雄性的攻击行为后，我们允许雌性在这两只雄性中进行配偶选择。仅雄性的攻击性表现出人格变异，雌性则未观察到此类现象。此外，无论雄性的攻击性水平如何，雌性普遍更偏好攻击性表现具有一致性的雄性。我们未发现雌性对雄性攻击性水平存在普遍偏好。但我们观察到，雌性对攻击性高且表现一致的雄性存在超出随机水平的偏好；而雌性对攻击性高但表现不一致的雄性的偏好，则与随机选择无显著差异。本研究结果表明，雄性彩虹短鲷的攻击性行为一致性可通过雌性配偶选择受到正向性选择。此外，本研究强调了在动物行为研究中，同时考量行为性状的水平与一致性的重要性。