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.

研究背景：辛普森曾提出适应性辐射（adaptive radiation）的概念模型，该模型指出演化支系可在广阔的适应性景观（adaptive landscape）中分化为多个「适应性区域」。然而，目前仅有少数研究真正针对适应性景观开展探究，并借此阐释表型演化（phenotypic evolution）的内在作用机制。在鱼类类群中，运动表型的演化是适应性辐射过程中生态形态多样性（ecomorphological diversification）分化的重要维度，因其与摄食策略及栖息地利用紧密相关。新热带界的土鲷亚科（Geophagini）慈鲷是新近被发现的适应性辐射类群，为探究运动模式的分化规律，以及选择性约束对表型分化的一般性影响提供了优质的研究体系。
研究结果：本研究采用表型演化的多元排序模型（multivariate ordination models）与后验预测方法（posterior predictive approaches），对土鲷亚科慈鲷的适应性景观展开探究，并检验其运动表型早期分化的相关证据。运动表型的演化呈现出向两个独立适应性峰值的定向分化选择（divergent selection）特征，同时伴随现代形态差异（morphological disparity）的早期分化。演化模型与后验预测方法均支持：驱动运动表型早期分化的核心过程为恒定速率的定向分化选择，而非表型演化速率随时间递减的过程。
研究结论：多个适应性峰值对土鲷亚科慈鲷运动性状分化的影响，契合生态驱动型适应性辐射的理论预期。本研究证实，运动形态的分化是土鲷亚科慈鲷适应性辐射过程中表型演化的重要维度。同时，本研究表明，适应性辐射过程中普遍观测到的表型演化早期爆发现象，最优解释模型为整合了系统发育（phylogeny）深层定向分化选择的演化模型。