Department of Comparative Biology and Experimental Medicine, Faculty of Veterinary Medicine, University of Calgary, Calgary, Canada.
Wiley Interdiscip Rev Dev Biol. 2020 Jul;9(4):e373. doi: 10.1002/wdev.373. Epub 2020 Jan 29.
Mammals have remarkably diverse limb proportions hypothesized to have evolved adaptively in the context of locomotion and other behaviors. Mechanistically, evolutionary diversity in limb proportions is the result of differential limb bone growth. Longitudinal limb bone growth is driven by the process of endochondral ossification, under the control of the growth plates. In growth plates, chondrocytes undergo a tightly orchestrated life cycle of proliferation, matrix production, hypertrophy, and cell death/transdifferentiation. This life cycle is highly conserved, both among the long bones of an individual, and among homologous bones of distantly related taxa, leading to a finite number of complementary cell mechanisms that can generate heritable phenotype variation in limb bone size and shape. The most important of these mechanisms are chondrocyte population size in chondrogenesis and in individual growth plates, proliferation rates, and hypertrophic chondrocyte size. Comparative evidence in mammals and birds suggests the existence of developmental biases that favor evolutionary changes in some of these cellular mechanisms over others in driving limb allometry. Specifically, chondrocyte population size may evolve more readily in response to selection than hypertrophic chondrocyte size, and extreme hypertrophy may be a rarer evolutionary phenomenon associated with highly specialized modes of locomotion in mammals (e.g., powered flight, ricochetal bipedal hopping). Physical and physiological constraints at multiple levels of biological organization may also have influenced the cell developmental mechanisms that have evolved to produce the highly diverse limb proportions in extant mammals. This article is categorized under: Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and Timing Comparative Development and Evolution > Regulation of Organ Diversity Comparative Development and Evolution > Organ System Comparisons Between Species.
哺乳动物的肢体比例具有显著的多样性，据推测，这些比例是在运动和其他行为的背景下适应性进化的。从机制上讲，肢体比例的进化多样性是肢体骨骼生长差异的结果。肢体骨骼的纵向生长是由软骨内骨化过程驱动的，受生长板的控制。在生长板中，软骨细胞经历一个严格协调的增殖、基质产生、肥大和细胞死亡/转分化的生命周期。这个生命周期在个体的长骨之间以及亲缘关系较远的类群的同源骨骼之间高度保守，导致了有限数量的互补细胞机制，可以产生肢体骨骼大小和形状的可遗传表型变异。其中最重要的机制是软骨发生和个体生长板中的软骨细胞群体大小、增殖率和肥大软骨细胞大小。哺乳动物和鸟类的比较证据表明，存在发育偏差，这些偏差有利于某些细胞机制在驱动肢体比例进化上的变化超过其他机制。具体来说，与肥大软骨细胞大小相比，软骨细胞群体大小可能更容易因选择而进化，而极度肥大可能是一种罕见的进化现象，与哺乳动物高度专业化的运动模式（如动力飞行、反弹式两足跳跃）有关。在多个生物组织层次的物理和生理限制也可能影响到进化产生现存哺乳动物高度多样化肢体比例的细胞发育机制。本文属于以下类别： 时空模式的建立 > 大小、比例和时间的调节 比较发育与进化 > 器官多样性的调节 比较发育与进化 > 物种间器官系统比较。
