Data from: Testing for unequal rates of morphological diversification in the absence of a detailed phylogeny: a case study from characiform fishes

This study develops the random phylogenies rate test (RAPRATE), a likelihood method that simulates morphological evolution along randomly generated phylogenies, and uses it to determine whether a considerable difference in morphological diversity between two sister clades of South American fishes should be taken as evidence of differing rates of morphological change or lineage turnover. Despite identical ages of origin, similar species richness, and sympatric geographic distributions, the morphological and ecological diversity of the superfamily Anostomoidea exceeds that of the Curimatoidea. The test shows with 90% confidence (using variance among species as the measure of morphological diversity) or 99% confidence (using volume of occupied morphospace) that the rate of morphological change per unit time in the Anostomoidea likely exceeded that of the Curimatoidea. Variation in the rate of lineage turnover (speciation and extinction rates) is not found to affect greatly the morphological diversity of simulated clades and is not a likely explanation of the observed difference in morphological diversity in this case study. Though a 17% or greater delay in the onset of diversification in the Curimatoidea remains a possible alternative explanation of unequal morphological diversification, further simulations suggest that two clades drawn from the possible treespace of the Anostomoidea and Curimatoidea will rarely differ so greatly in the onset of diversification. Several uniquely derived morphological and ecological features of the Anostomoidea and Curimatoidea may have accelerated or decelerated their rate of morphological change, including a marked lengthening of the quadrate that may have relaxed structural constraints on the evolution of the anostomoid jaw.

本研究构建了随机系统发育速率检验（random phylogenies rate test, RAPRATE）方法——一种可沿随机生成的系统发育树模拟形态演化的似然法（likelihood method），并利用该方法探究：南美鱼类的两个姊妹支系间存在的显著形态多样性差异，是否可作为形态变化速率或谱系更替速率存在差异的证据。尽管二者起源时间一致、物种丰富度相近且地理分布同域，但上口总科（Anostomoidea）的形态与生态多样性远超锯唇总科（Curimatoidea）。该检验结果显示，以物种间方差作为形态多样性衡量指标时置信度达90%，以占据的形态空间体积（morphospace）作为衡量指标时置信度达99%，表明上口总科单位时间内的形态变化速率大概率高于锯唇总科。谱系更替速率（speciation and extinction rates，即物种形成与灭绝速率）的差异未被发现对模拟支系的形态多样性产生显著影响，因此并非本案例中观测到的形态多样性差异的合理解释。尽管锯唇总科的分化起始时间延迟17%及以上仍可作为形态分化不均的潜在替代解释，但进一步模拟结果表明，取自上口总科与锯唇总科可能树空间（treespace）的两个支系，其分化起始时间极少出现如此巨大的差异。上口总科与锯唇总科的若干独有衍生形态与生态特征，可能分别加速或减缓了其形态变化速率——例如，方骨（quadrate）显著延长可能放松了上口总科颌骨演化的结构约束。