Data from: Heterospecific aggression bias towards a rarer colour morph

Colour polymorphisms are a striking example of phenotypic diversity, yet the sources of selection that allow different morphs to persist within populations remain poorly understood. In particular, despite the importance of aggression in mediating social dominance, few studies have considered how heterospecific aggression might contribute to the maintenance or divergence of different colour morphs. To redress this gap, we carried out a field-based study in a Nicaraguan crater lake to investigate patterns of heterospecific aggression directed by the cichlid fish, Hypsophrys nicaraguensis, towards colour polymorphic cichlids in the genus Amphilophus. We found that H. nicaraguensis was the most frequent territorial neighbour of the colour polymorphic A. sagittae. Furthermore, when manipulating territorial intrusions using models, H. nicaraguensis were more aggressive towards the gold than dark colour morph of the sympatric Amphilophus species, including A. sagittae. Such a pattern of heterospecific aggression should be costly to the gold colour morph, potentially accounting for its lower than expected frequency and, more generally, highlighting the importance of considering heterospecific aggression in the context of morph frequencies and coexistence in the wild.

体色多态现象（colour polymorphism）是表型多样性的显著例证，但支撑不同体色形态在种群内持续共存的选择压力来源，目前仍未得到充分解析。具体而言，尽管攻击行为在调控社会等级中发挥关键作用，但鲜有研究探讨异种攻击行为（heterospecific aggression）如何影响不同体色形态的维持与分化。为弥补这一研究空白，我们在尼加拉瓜的一处火山口湖开展野外研究，探究尼加拉瓜厚唇丽鱼（Hypsophrys nicaraguensis）对双冠丽鱼属（Amphilophus）内体色多态慈鲷鱼类的异种攻击行为模式。研究发现，尼加拉瓜厚唇丽鱼是箭形双冠丽鱼（Amphilophus sagittae，简称A. sagittae）最常见的领地邻体。此外，通过模型模拟领地入侵实验发现，相较于深色体色形态，尼加拉瓜厚唇丽鱼对同域分布的双冠丽鱼属物种（包括箭形双冠丽鱼）的金色体色形态表现出更强的攻击性。这种异种攻击行为模式会对金色体色形态个体造成适合度成本，这或许可以解释其野外种群中出现频率低于预期的原因；更广泛而言，该研究凸显了在体色形态频率与野外物种共存的研究框架中，考量异种攻击行为的重要性。