van den Berg Cedric P, Hassler Gabriel W, Blomberg Simone P, Wilson Nerida G, Suchard Marc A, Cheney Karen L
School of the Environment, The University of Queensland, Brisbane, Queensland, Australia.
School of Biological Sciences, Bristol University, Bristol, UK.
J Anim Ecol. 2025 Jun;94(6):1165-1179. doi: 10.1111/1365-2656.70036. Epub 2025 Apr 15.
Visually hunting predators drive the evolution and maintenance of bold visual defences, including aposematic signalling. Such visual signals must be encountered by predators in lighting conditions where the perception of colour patterns is possible. Therefore, aposematic colouration is predicted to evolve in species encountered by visually hunting predators during daytime, with diurnal species most at risk of visual predation. However, colour patterns in diurnal and nocturnal species are highly diverse, and little is known about the relationships between prey colouration and daytime activity. To investigate correlations between daytime activity and colour pattern phenotypes across species, we quantified colour patterns in 45 species (n = 346 individuals) of eastern Australian sea slugs (Gastropoda: Heterobranchia). We used 158 descriptors of colour pattern morphology using the Quantitative Colour Pattern Analysis (QCPA) framework, which models pattern appearance using the visual system of a potential predator, a triggerfish (Rhinecanthus aculeatus). We then used phylogenetic factor analysis to identify a single factor that was strongly correlated with daytime activity, comprising 55 individual colour pattern descriptors. This dimension of pattern variation identified daytime activity in 87% of species in our dataset. We found that daytime activity in heterobranch sea slugs was associated with a distinct, highly descriptive set of spatiochromatic image statistics. Specifically, diurnal species were more boldly patterned than nocturnal species, exhibiting increased colour, luminance and pattern contrast, indicating the presence of visual signalling and, thus, visual predation as a key driver of heterobranch sea slug phenotype. Our study sheds light on the ecology and evolution of defensive colouration in sea slugs and provides a novel and robust workflow for comparative phylogenetic studies considering colour pattern spaces described by high-dimensional datasets, which can be applied to other species and ecosystems.
视觉捕食性捕食者推动了包括警戒信号在内的醒目视觉防御的进化与维持。此类视觉信号必须在捕食者能够感知颜色模式的光照条件下被其遇到。因此，预计警戒色会在白天遭遇视觉捕食性捕食者的物种中进化，昼行性物种面临视觉捕食的风险最高。然而，昼行性和夜行性物种的颜色模式高度多样，关于猎物颜色与日间活动之间的关系知之甚少。为了研究跨物种日间活动与颜色模式表型之间的相关性，我们对澳大利亚东部海蛞蝓（腹足纲：异鳃亚纲）的45个物种（n = 346个体）的颜色模式进行了量化。我们使用定量颜色模式分析（QCPA）框架中的158个颜色模式形态描述符，该框架使用潜在捕食者——扳机鱼（黑背鼻鱼）的视觉系统对模式外观进行建模。然后，我们使用系统发育因子分析来确定与日间活动密切相关的单一因子，该因子由55个个体颜色模式描述符组成。这种模式变化维度在我们数据集中87%的物种中识别出了日间活动。我们发现，异鳃海蛞蝓的日间活动与一组独特的、高度描述性的空间颜色图像统计数据相关。具体而言，昼行性物种的图案比夜行性物种更大胆，表现出颜色、亮度和图案对比度增加，表明存在视觉信号，因此视觉捕食是异鳃海蛞蝓表型的关键驱动因素。我们的研究揭示了海蛞蝓防御性色彩的生态学和进化，并为考虑高维数据集描述的颜色模式空间的比较系统发育研究提供了一种新颖且稳健的工作流程，该流程可应用于其他物种和生态系统。
