Hamrick Mark W
Department of Cellular Biology & Anatomy, Medical College of Georgia, Augusta, Georgia 30912, USA.
J Exp Zool B Mol Dev Evol. 2003 Aug 15;298(1):152-63. doi: 10.1002/jez.b.32.
The adaptive radiation of mammalian clades has involved marked changes in limb morphology that have affected not only the skeleton but also the integumentary structures. For example, didelphid marsupials show distinct differences in nail and claw morphology that are functionally related to the evolution of arboreal, terrestrial, and aquatic foraging behaviors. Vespertilionoid bats have evolved different volar pad structures such as adhesive discs, scales, and skin folds, whereas didelphid marsupials have apical pads covered either with scales, ridges, or small cones. Comparative analysis of pad and claw development reveals subtle differences in mesenchymal and ectodermal patterning underlying interspecific variation in morphology. Analysis of gene expression during pad and claw development reveals that signaling molecules such as Msx1 and Hoxc13 play important roles in the morphogenesis of these integumentary structures. These findings suggest that evolutionary change in the expression of these molecules, and in the response of mesenchymal and ectodermal cells to these signaling factors, may underlie interspecific differences in nail, claw, and volar pad morphology. Evidence from comparative morphology, development, and functional genomics therefore sheds new light on both the patterns and mechanisms of evolutionary change in mammalian limb integumentary structures.
哺乳动物各分支的适应性辐射涉及肢体形态的显著变化，这些变化不仅影响骨骼，还影响体表结构。例如，负鼠目有袋动物在指甲和爪子形态上表现出明显差异，这些差异在功能上与树栖、陆地和水生觅食行为的进化有关。蝙蝠科蝙蝠进化出了不同的掌垫结构，如吸盘、鳞片和皮肤褶皱，而负鼠目有袋动物的顶端垫则覆盖着鳞片、嵴或小圆锥体。对掌垫和爪子发育的比较分析揭示了种间形态差异背后间充质和外胚层模式形成的细微差别。对掌垫和爪子发育过程中基因表达的分析表明，Msx1和Hoxc13等信号分子在这些体表结构的形态发生中起重要作用。这些发现表明，这些分子表达的进化变化以及间充质和外胚层细胞对这些信号因子的反应，可能是指甲、爪子和掌垫形态种间差异的基础。因此，来自比较形态学、发育学和功能基因组学的证据为哺乳动物肢体体表结构进化变化的模式和机制提供了新的线索。
