Female preference for colour-enhanced males: a test of the sensory bias model in medaka, a drab fish

Sexual selection research has long focused on the evolution of female mate preferences. Most of the models that have been developed posit that mate preferences evolve in a mating context. In contrast, the sensory bias model proposes that mate choice preferences arise in a non-mating context, as a by-product of natural selection acting on a female’s perceptual system. Recent research has shown that many species of fishes, from across a large clade including poeciliids, goodeids, and medaka, have a bias for long wavelength (LW) colors (yellow, orange, red) in a non-mating context. Even species that do not have LW-colored ornaments, apparently because they have been lost secondarily, retain this latent bias for LW colors. Here, we predicted that female Oryzias latipes (Japanese medaka), a drab species with a latent preference for LW colors, would show a mate choice preference for males with an artificial secondary sexual trait—a colored stripe added to their flank. We confirmed that females were more responsive to red and orange objects in a non-mating context than to other colors. We also showed that females were less resistant towards males with a LW-colored stripe than to those enhanced with a non-LW stripe and that, for many females, responses towards specific LW colors were consistent across these non-mating and mating contexts. Therefore, our results provide support for the sensory bias model by providing a link between a sensory bias in a non-mating context and a mate choice preference in a drab species like medaka.

Methods
Data set we collected using JWatcher while watching behavioural observations. Data processing was done in JMP©14.0 (SAS Institute, Inc. 2018) for the divided tank data, and in RStudio (ver.1.4.1103) for the free swim data and the comparison across two behavioral contexts; the disc test data were analysed using both software programs.

性选择研究长期以来一直聚焦于雌性配偶偏好的演化。现有多数已构建的模型均假定，配偶偏好是在交配情境中演化而来的。与之相对，感官偏向模型（sensory bias model）则提出，配偶选择偏好起源于非交配情境，是作用于雌性感知系统的自然选择的副产物。
近期研究表明，涵盖花鳉科（poeciliids）、谷鳉科（goodeids）以及青鳉（medaka）在内的多个大类群的诸多鱼类，在非交配情境中均表现出对长波长（long wavelength, LW）色彩（黄色、橙色、红色）的偏向。即便部分鱼类本身不具备长波长色彩的装饰结构——这显然是次生丢失所致——它们仍保留了对长波长色彩的潜在偏向。
本研究中，我们预测体色平淡且具备长波长色彩潜在偏好的日本青鳉（Oryzias latipes, Japanese medaka）雌性，会对带有人工次生性征（即在体侧添加彩色条纹）的雄性表现出配偶选择偏好。我们证实，雌性在非交配情境中对红色与橙色物体的响应程度显著高于其他色彩。此外我们还发现，相较于带有非长波长色彩条纹的雄性，雌性对带有长波长色彩条纹的雄性的抗拒程度更低；且对于多数雌性而言，它们对特定长波长色彩的响应在非交配与交配两种情境中保持一致。综上，本研究通过建立非交配情境中的感官偏向与青鳉这类体色平淡物种的配偶选择偏好之间的关联，为感官偏向模型提供了实证支持。

方法
本研究的数据集通过JWatcher软件，在回放行为观测录像时采集得到。分隔水箱实验数据的处理使用JMP©14.0（SAS研究所，2018年）完成；自由游动实验数据以及两种行为情境间的比较分析则通过RStudio（版本1.4.1103）完成；圆盘测试实验数据则同时使用上述两款软件进行分析。