Astudillo-Clavijo Viviana, Arbour Jessica H, López-Fernández Hernán
Department of Ecology and Evolutionary Biology, University of Toronto, 25 Wilcocks St, Toronto, Ontario, M5S 3B2, Canada.
Department of Natural History, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario, M5S 2C6, Canada.
BMC Evol Biol. 2015 May 1;15:77. doi: 10.1186/s12862-015-0348-7.
Simpson envisaged a conceptual model of adaptive radiation in which lineages diversify into "adaptive zones" within a macroevolutionary adaptive landscape. However, only a handful of studies have empirically investigated this adaptive landscape and its consequences for our interpretation of the underlying mechanisms of phenotypic evolution. In fish radiations the evolution of locomotor phenotypes may represent an important dimension of ecomorphological diversification given the implications of locomotion 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.
We use multivariate ordination, models of phenotypic evolution and posterior predictive approaches to investigate the macroevolutionary adaptive landscape and test for evidence of early divergence of locomotor phenotypes in Geophagini. The evolution of locomotor phenotypes was characterized by selection towards at least two distinct adaptive peaks and the early divergence of modern morphological disparity. One adaptive peak included the benthic and epibenthic invertivores and was characterized by fishes with deep, laterally compressed bodies that optimize precise, slow-swimming manoeuvres. The second adaptive peak resulted from a shift in adaptive optima in the species-rich ram-feeding/rheophilic Crenicichla-Teleocichla clade and was characterized by species with streamlined bodies that optimize fast starts and rapid manoeuvres. Evolutionary models and posterior predictive approaches favoured an early shift to a new adaptive peak over decreasing rates of evolution as the underlying process driving the early divergence of locomotor phenotypes.
The influence of multiple adaptive peaks on the divergence of locomotor phenotypes in Geophagini is compatible with the expectations of an ecologically driven adaptive radiation. This study confirms that the diversification of locomotor phenotypes 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 may be better explained by the concentration of shifts to new adaptive peaks deep in the phylogeny rather than overall decreasing rates of evolution.
辛普森设想了一个适应性辐射的概念模型，在这个模型中，谱系在宏观进化的适应性景观中分化为“适应区”。然而，只有少数研究对这种适应性景观及其对我们解释表型进化潜在机制的影响进行了实证研究。在鱼类辐射中，考虑到运动对觅食和栖息地利用的影响，运动表型的进化可能代表了生态形态分化的一个重要维度。新热带地区的食土丽鱼科丽鱼代表了一个新发现的适应性辐射，为研究运动多样化模式以及一般选择性限制对表型分化的影响提供了一个有用的系统。
我们使用多元排序、表型进化模型和后验预测方法来研究宏观进化的适应性景观，并检验食土丽鱼科中运动表型早期分化的证据。运动表型的进化特征是朝着至少两个不同的适应峰进行选择以及现代形态差异的早期分化。一个适应峰包括底栖和浅栖食虫动物，其特征是身体深且侧扁的鱼类，这种身体形态优化了精确、缓慢的游泳动作。第二个适应峰是由于物种丰富的猛冲摄食/喜流的丽鱼属 - 远鳍丽鱼属分支中适应最优值的转变导致的，其特征是身体流线型的物种，这种身体形态优化了快速启动和快速动作。进化模型和后验预测方法支持早期向新的适应峰转变，而不是进化速率降低，将其作为驱动运动表型早期分化的潜在过程。
多个适应峰对食土丽鱼科中运动表型分化的影响与生态驱动的适应性辐射的预期相符。这项研究证实，运动表型的多样化代表了食土丽鱼科适应性辐射中表型进化的一个重要维度。它还表明，在适应性辐射期间通常观察到的表型进化早期爆发可能更好地由系统发育深处向新适应峰的转变集中来解释，而不是整体进化速率降低。
