Data from: What makes a multimodal signal attractive? A preference function approach

Courtship signals are often complex and include components within and across sensory modalities. Unfortunately, the evidence for how multimodal signals affect female preference functions is still rather limited. This is an important scientific gap because preference function shape can indicate which male traits are under the strongest selection. We modelled how preference function shape can be altered under 4 scenarios of varying signal content, including both redundant and non-redundant signals. The model was tested with the brown-headed cowbird (Molothrus ater); we manipulated male song attractiveness and visual display intensity, and assessed female preferences in an audiovisual playback study. We found that the intensity of a visual display can modify how attractive a song is for females. This indicates that the visual and acoustic male signal components are non-redundant and modulate each other. Our study shows a change in the direction of female preference functions for one signalling modality resulting from changes in the attractiveness of the other modality. Overall, our findings suggest that male signals in this species may not be under the typical directional selection documented in other species, but rather selection may favour males that possess a range of different signals that can be used strategically during different social contexts.求偶信号通常结构复杂，涵盖单一感官模态（sensory modality）内部与跨感官模态的多重组成成分。遗憾的是，目前关于多模态信号（multimodal signals）如何影响雌性偏好函数的相关研究证据仍较为匮乏。这一科学空白具有重要的科学意义，因为偏好函数的形态可揭示哪些雄性性状承受着最强的选择压力。我们构建模型并分析了偏好函数形态在4种不同信号内容变化情景下的改变规律，其中情景涵盖冗余信号与非冗余信号两种类型。我们以棕头牛鹂（Molothrus ater）为实验对象验证该模型：通过操控雄性鸣唱的吸引力水平与视觉展示强度，在音视频回放实验中评估雌性的择偶偏好。研究结果表明，视觉展示的强度可改变雌性对雄性鸣唱的吸引力评价。这意味着雄性的视觉与声学信号成分并非冗余，而是可相互调控。本研究还发现，单一信号模态的雌性偏好函数方向，会因另一模态信号吸引力的变化而发生改变。综合来看，本研究结果提示，该物种的雄性求偶信号可能并未承受其他物种中常见的定向选择压力；相反，自然选择更倾向于那些拥有多样化信号组合、可在不同社会情境下策略性运用信号的雄性个体。