Data from: Morphological integration in the appendicular skeleton of two domestic taxa: the horse and donkey.

Organisms are organized into suites of anatomical structures that typically covary when developmentally or functionally related, and this morphological integration plays a determinant role in evolutionary processes. Artificial selection on domestic species causes strong morphological changes over short time spans, frequently resulting in a wide and exaggerated phenotypic diversity. This raises the question of whether integration constrains the morphological diversification of domestic species and how natural and artificial selection may impact integration patterns. Here, we study the morphological integration in the appendicular skeleton of domestic horses and donkeys, using 3D geometric morphometrics on 75 skeletons. Our results indicate that a strong integration is inherited from developmental mechanisms which interact with functional factors. This strong integration reveals a specialization in the locomotion of domestic equids, partly for running abilities. We show that the integration is stronger in horses than in donkeys, probably because of a greater degree of specialization and predictability of their locomotion. Thus the constraints imposed by integration are weak enough to allow important morphological changes and the phenotypic diversification of domestic species.

生物体内的解剖结构通常会以协同变异的形式，组成具有发育或功能关联的结构组合，这种形态整合（morphological integration）在演化进程中发挥决定性作用。对家养物种实施的人工选择可在短时间内引发剧烈的形态变异，往往催生广泛且夸张的表型多样性（phenotypic diversity）。这引出了一个关键科学问题：形态整合是否会限制家养物种的形态多样化进程，以及自然选择与人工选择如何作用于整合模式。本研究以75件骨骼标本为研究对象，采用三维几何形态测量学（3D geometric morphometrics）方法，探究家养马与驴的附肢骨骼（appendicular skeleton）形态整合特征。研究结果显示，较强的形态整合源自发育机制，并与功能因素相互作用。这种强烈的形态整合反映了家养马科动物（equids）的运动特化，其中部分特化适配奔跑能力。研究发现，马的形态整合强度高于驴，这可能源于马的运动方式特化程度更高，且运动模式更具可预测性。由此可见，形态整合所施加的演化约束足够微弱，足以允许家养物种发生显著的形态变异并实现表型多样化。