Data for: Multilevel analysis of integration and disparity in the mammalian skull

Biological variation is often considered in a scalable hierarchy, e.g., within the individual, within the populations, above the species level. Morphological integration, the concept of covariation among constituent parts of an organism, is also hierarchical; the degree to which these ‘modules’ covary is a matter of the scale of the study as well as underlying processes driving the covariation. Multilevel analyses of trait covariation are a valuable tool to infer the origins and historical persistence of morphological diversity. Here we investigate concordance in patterns of integration and modularity across three biological levels of variation: within a species, within two genera-level radiations, and among species at the family level. We demonstrate this approach using the skull of mammalian family Leporidae (rabbits and hares), which is morphologically diverse and has a rare-among-mammals functional signal of locomotion adaptation. We tested three alternative hypotheses of modularity; from the most supported we investigated disparity and integration of each module to infer which is most responsible for patterns of cranial variation across these levels, and whether variation is partitioned consistently across levels. We found a common pattern of modularity underlies leporid cranial diversity, though there is inconsistency across levels in each module’s disparity and integration. The face module contributes the most to disparity at all levels, which we propose is facilitating evolutionary diversity in this clade. Therefore, the distinctive facial tilt of leporids is an adaptation to locomotory behavior facilitated by a modular system that allows lineages to respond differently to selection pressures.生物变异通常可置于可拓展的层级框架下进行分析，例如个体内部、种群内部以及物种以上层级。形态整合（Morphological integration）指生物体各组成部分间的协变异关系，同样具有层级结构；这些‘模块’间的协变异程度，既取决于研究尺度，也受驱动协变异的内在过程影响。性状协变异的多层级分析是推断形态多样性起源与历史存续性的有效工具。本研究旨在探究三类生物变异层级下的整合与模块化模式一致性：物种内部、两个属级适应辐射类群内部，以及科级水平的物种种间。我们以哺乳纲兔科（Leporidae，兔与野兔）的头骨为研究对象验证该方法：该类群形态多样性丰富，且拥有哺乳类中罕见的运动适应功能信号。我们针对模块化结构提出了三种备选假说，并基于支持度最高的假说，对各模块的形态差异度与整合性展开分析，以推断在上述层级中哪些模块对颅骨变异模式的贡献最大，同时验证变异在各层级间的分配是否保持一致。研究发现，兔科动物的颅骨多样性背后存在统一的模块化模式，但各模块的形态差异度与整合性在不同层级间并不一致。面部模块在所有层级中对形态差异度的贡献均为最高，我们据此推测该模块推动了该演化支的演化多样性。因此，兔科动物独特的面部倾斜结构，是对运动行为的适应性演化结果，这一模块化系统使得不同演化支能够对选择压力做出差异化响应。