Department of Biology, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, 3900 Avenida dos Bandeirantes, 14040-901, Ribeirão Preto, SP, Brazil.
Département Adaptations du Vivant, Muséum National d'Histoire Naturelle, 55 Rue Buffon 75005, Paris, France.
Proc Biol Sci. 2022 Jan 12;289(1966):20212300. doi: 10.1098/rspb.2021.2300.
Selective regimes favouring the evolution of functional specialization probably affect covariation among phenotypic traits. Phalanges of most tetrapods develop from a conserved module that constrains their relative proportions. In geckos, however, biomechanical specializations associated with adhesive toepads involve morphological variation in the autopodium and might reorganize such modular structures. We tested two hypotheses to explain the modular architecture of hand bones in geckos, one based on developmental interactions and another incorporating functional associations related to locomotion, and compared the empirical support for each hypothetical module between padded and padless lineages. We found strong evidence for developmental modules in most species, which probably reflects embryological constraints during phalangeal formation. Although padded geckos exhibit a functional specialization involving the hyperextension of the distal phalanges that is absent in padless species, the padless species are the ones that show a distal functional module with high integration. Some ancestrally padless geckos apparently deviate from developmental predictions and present a relatively weak developmental module of phalanges and a strongly integrated distal module, which may reflect selective regimes involving incipient frictional adhesion in digit morphology. Modularity of digit elements seems dynamic along the evolutionary history of geckos, being associated with the presence/absence of adhesive toepads.
选择性进化可能会影响表型特征之间的协同进化。大多数四足动物的指骨是从一个保守的模块发育而来的，这个模块限制了它们的相对比例。然而，在壁虎中，与粘性脚垫相关的生物力学特化涉及到附肢的形态变化，可能会重新组织这种模块结构。我们提出了两个假说来解释壁虎手部骨骼的模块结构，一个基于发育相互作用，另一个则包含与运动相关的功能关联，并比较了有垫和无垫谱系之间每个假设模块的经验支持。我们发现，在大多数物种中，都有强烈的发育模块证据，这可能反映了指骨形成过程中的胚胎学限制。尽管有垫壁虎表现出一种涉及远端指骨过度伸展的功能特化，而无垫物种则不存在这种特化，但无垫物种的远端功能模块具有较高的整合度。一些祖先上无垫的壁虎显然偏离了发育预测，表现出相对较弱的指骨发育模块和高度整合的远端模块，这可能反映了涉及指数字形态初始摩擦粘附的选择作用。指骨元素的模块性似乎沿着壁虎的进化历史是动态的，与粘性脚垫的存在/缺失有关。
