Data from: Selection towards different adaptive optima drove the early diversification of locomotor phenotypes in the radiation of Neotropical geophagine cichlids

Background: Simpson envisaged a conceptual model of adaptive radiation in which lineages diversify into "adaptive zones" within a broad adaptive landscape. However only a handful of studies have actually investigated the adaptive landscape and its implication for our interpretation of the underlying mechanisms of phenotypic evolution. In fishes the evolution of locomotor phenotypes may represent an important dimension of ecomorphological diversification during an adaptive radiation given its implications for feeding and habitat use. Neotropical geophagine cichlids represent a newly identified adaptive radiation and provide a useful system for studying patterns of locomotor diversification and the implications of selective constraints on phenotypic divergence in general. Results: We use multivariate ordination models of phenotypic evolution and posterior predictive approaches to investigate the adaptive landscape and test for evidence of early diversification of locomotor phenotypes in Geophagini. The evolution of locomotor phenotypes was characterized by divergent selection towards two distinct adaptive peaks and the early divergence of modern morphological disparity. Evolutionary models and posterior predictive approaches favoured constant-rate divergent selection over decreasing rates of phenotypic evolution as the underlying process driving the early divergence of locomotor phenotypes. Conclusions: The influence of multiple adaptive peaks on the divergence of locomotor attributes in Geophagini is compatible with the expectations of an ecologically-driven adaptive radiation. This study confirms that the diversification of locomotor morphology represents an important dimension of phenotypic evolution in the geophagine adaptive radiation. It also suggests that the commonly observed early burst of phenotypic evolution during adaptive radiations is best explained by a model that incorporates divergent selection deep in the phylogeny.

背景：辛普森曾设想了适应辐射（adaptive radiation）的概念模型，即演化类群在广阔的适应景观（adaptive landscape）内分化为多个“适应区（adaptive zone）”。然而，目前仅有少数研究实际探究了适应景观及其对解读表型进化（phenotypic evolution）潜在机制的启示意义。在鱼类类群中，运动表型（locomotor phenotypes）的演化或代表了适应辐射过程中生态形态分化（ecomorphological diversification）的重要维度，因其与摄食策略及栖息地利用模式紧密相关。新热带土丽鱼族（Neotropical geophagine cichlids）是新近被确认的适应辐射类群，为研究运动分化模式，以及选择限制对表型分化的普遍影响提供了理想的研究体系。
结果：本研究采用表型进化的多变量排序模型（multivariate ordination models）与后验预测方法（posterior predictive approaches），对土丽鱼族的适应景观展开探究，并检验其运动表型早期分化的相关证据。研究发现，运动表型的演化以歧化选择（divergent selection）导向两个独立的适应峰（adaptive peaks），以及现代类群形态差异度（morphological disparity）的早期分化为核心特征。进化模型与后验预测方法均支持，以恒定速率的歧化选择而非不断减缓的表型进化速率，作为驱动运动表型早期分化的核心演化过程。
结论：多个适应峰对土丽鱼族运动性状分化的影响，契合生态驱动型适应辐射的理论预期。本研究证实，运动形态的分化是土丽鱼族适应辐射过程中表型进化的关键维度。同时，本研究表明，适应辐射过程中普遍观测到的表型进化早期爆发现象，最适宜通过纳入系统发育（phylogeny）早期歧化选择的演化模型加以解释。