Data from: Brain size affects the behavioral response to predators in female guppies (Poecilia reticulata)

Large brains presumably result from selection for cognitive benefits, but how enhanced cognition leads to increased fitness remains poorly understood. One explanation is that increased cognitive ability results in improved monitoring and assessment of predator threats. Here we use male and female guppies (Poecilia reticulata) artificially selected for large and small brain size to provide an experimental evaluation of this hypothesis. We examined their behavioral response as singletons, pairs or shoals of four towards a model predator. Large-brained females, but not males, spent less time performing predator inspections, an inherently risky behavior. Video analysis revealed that large-brained females were further away from the model predator when in pairs but that they habituated quickly towards the model when in shoals of four. Males consistently stayed further away from the predator model than females but again we found no brain size effect in males. We conclude that manipulating brain size changed female predator response. Large-brained females might be able to assess risk better or need less sensory information to reach an accurate conclusion. Our results provide experimental support for the general idea that predation pressure is likely to be important for the evolution of brain size in prey species.大脑体积较大通常被认为是定向选择认知优势的结果，但增强的认知能力如何提升生存适合度，目前仍不甚明晰。现有假说认为，认知能力提升可优化对捕食者威胁的监测与评估。本研究以经人工选育获得大脑体积大和大脑体积小的雌雄孔雀花鳉（Poecilia reticulata，孔雀鱼）为实验对象，对该假说开展实验验证。我们分别检测了它们以单只、成对或4尾集群形式面对模型捕食者（model predator）时的行为反应。结果显示，大脑体积较大的雌性个体（而非雄性）花费在捕食者巡查（predator inspections）——一种固有风险的行为——上的时间更少。视频分析进一步表明，成对状态下大脑体积较大的雌性个体与模型捕食者的距离更远，但当以4尾集群形式存在时，它们会更快习惯化接近模型捕食者。雄性个体始终比雌性个体更远离模型捕食者，但在雄性个体中未观察到大脑体积对行为的影响。本研究结论表明，调控大脑体积可改变雌性个体对捕食者的行为反应。大脑体积较大的雌性个体或许能够更精准地评估风险，或是仅需更少的感官信息即可得出准确的风险判断。本研究结果为"捕食压力可能在猎物物种大脑体积的进化过程中发挥关键作用"这一通用观点提供了实验支撑。