Supplementary information from "Geographic visual signal trends in neotropical frogs and their environmental predictors"

Visual signals are a widespread behavioral attribute of communication among vertebrates. This behavior is often utilized during intrasexual competition or to attract mates and is directly linked to reproductive success. However, information regarding the extrinsic factors driving the evolution of visual signals is generally lacking. Herein, we investigated trends of visual signal variation and the complexity in frogs related to humidity and vegetative heterogeneity throughout the Neotropical region. We constructed a dataset comprised of 236 frog species with visual signals in the Neotropical region based on a literature search. We performed spatial and phylogenetic regressions using potential evapotranspiration and canopy height as humidity and environmental heterogeneity proxies, respectively. Our findings indicate that species richness of frogs with visual signals tends to be higher in drier locations with more homogeneous vegetation. Spatial regressions showed that visual signal complexity tended to be higher in locations with more homogeneous vegetation. On the other hand, phylogenetic regressions showed that neither species richness with visual signals nor visual signal complexity were explained merely by environment. We suggest that frogs perform visual signals in drier locations with more homogeneous vegetation to maximize reproductive success with higher effectiveness of signal transmission while resources are available. Frogs with a more elaborated visual repertoire in locations with more homogeneous vegetation could be explained by selective forces, acting on individuals’ capability of communicating through a simpler background and reduced obstruction. However, the correlation of visual signals with frog richness followed by the absence of visual signal trends, considering evolutionary relationships, suggests that other factors should be considered to better predict visual signal trends. Given their remarkable behavioral diversity, frogs have the potential to serve as an excellent model for understanding visual signal evolution in vertebrates.

视觉信号是脊椎动物间通讯行为中广泛存在的一类行为特征。此类行为常被用于种内竞争或求偶，并直接与繁殖成功率相关。然而，目前关于驱动视觉信号演化的外在影响因素的相关信息仍较为匮乏。本研究针对新热带区（Neotropical region）的蛙类展开，探究了其视觉信号变异趋势以及与湿度、植被异质性相关的视觉信号复杂度。本研究通过文献检索，构建了包含新热带区236种具有视觉信号的蛙类的数据集。本研究分别以潜在蒸散量（potential evapotranspiration）和冠层高度（canopy height）作为湿度和环境异质性的替代指标，开展了空间回归（spatial regressions）与系统发育回归（phylogenetic regressions）分析。研究结果显示，在植被更均一的干旱生境中，具有视觉信号的蛙类物种丰富度往往更高。空间回归分析表明，植被更均一的生境中蛙类的视觉信号复杂度往往更高。而系统发育回归分析则显示，具有视觉信号的蛙类物种丰富度与视觉信号复杂度均无法仅通过环境因素解释。我们推测，在资源可获得的前提下，蛙类在植被更均一的干旱生境中开展视觉信号行为，可通过提升信号传递效率最大化繁殖成功率。对于在植被更均一的生境中拥有更精细视觉信号库的蛙类，这一现象可通过选择压力解释：此类选择压力作用于个体在更简单、干扰更少的背景下进行通讯的能力。然而，考虑演化关系后，视觉信号与蛙类物种丰富度存在相关性，但视觉信号并未呈现出明显的演化趋势，这提示我们需要纳入其他因素才能更准确地预测视觉信号的演化趋势。鉴于蛙类具备极为丰富的行为多样性，它们有望成为探究脊椎动物视觉信号演化的优质研究模型。