Data from: The ecology of a continental evolutionary radiation: Is the radiation of sigmodontine rodents adaptive?

Evolutionary radiations on continents are less well understood and appreciated than those occurring on islands. The extent of ecological influence on species divergence can be evaluated to determine whether a radiation was ultimately the outcome of divergent natural selection or else arose mainly by non-ecological divergence. Here, we used phylogenetic comparative methods to test distinct hypotheses corresponding to adaptive and non-adaptive evolutionary scenarios for the morphological evolution of sigmodontine rodents. Results showed that ecological variables (diet and life-mode) explain little of the shape and size variation of sigmodontine skulls and mandibles. A Brownian model with varying rates for insectivory versus all other diets was the most likely evolutionary model. The insectivorous sigmodontines have a faster rate of morphological evolution than mice feeding on other diets, possibly due to stronger selection for features that aid insectivory. We also demonstrate that rapid early-lineage diversification is not accompanied by high morphological divergence among sub-clades, contrasting with island results. The geographic size of continents permits spatial segregation to a greater extent than on islands, allowing for allopatric distributions and escape from interspecific competition. We suggest that continental radiations of rodents are likely to produce a pattern of high species diversification coupled with a low degree of phenotypic specialization.

相较于岛屿上的物种演化辐射，大陆上的演化辐射现象迄今尚未得到充分的认知与重视。我们可通过评估生态作用对物种分化的影响程度，判断某一演化辐射最终是趋异自然选择的结果，还是主要源于非生态性的物种分化。本研究采用系统发育比较方法（phylogenetic comparative methods），针对西啮鼠类（sigmodontine rodents）的形态演化，检验对应适应性与非适应性演化情境的不同假说。研究结果显示，生态变量（食性与生活型）对西啮鼠类的头骨与下颌骨的形态大小变异解释度极低。针对食虫与其他所有食性类群设置不同演化速率的布朗运动模型（Brownian model），为最具支持度的演化模型。食虫性西啮鼠类的形态演化速率快于其他食性的鼠类，这可能源于对利于食性特化的性状的更强选择压。本研究同时证实，早期谱系的快速多样化并未伴随亚分支间显著的形态分化，这与岛屿类群的研究结果相悖。大陆的地理幅员较岛屿更为广阔，更易实现种群的空间隔离，进而形成异域分布格局并摆脱种间竞争。据此我们提出，啮齿类的大陆演化辐射大概率会呈现出“物种多样性高但表型特化程度低”的演化格局。