Fast running restricts evolutionary change of the vertebral column in mammals
Fast running restricts evolutionary change of the vertebral column in mammals
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DOI：
10.1073/pnas.1401392111
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发表时间：
2014-08-05
影响因子：
11.1
通讯作者：
ten Broek, Clara M. A.
中科院分区：
文献类型：
--
作者：
Galis, Frietson;Carrier, David R.;ten Broek, Clara M. A.
哺乳动物的脊柱高度多变，反映了对各种生活方式的适应，从鼹鼠的洞穴到蝙蝠的飞行。然而，在许多分类群中，主干椎体的数量出人意料地恒定。我们认为，在快速奔跑和敏捷的哺乳动物中，这种恒定是由于对这些数量的初始变化进行了强烈的选择，而在跑得更慢、更强壮的哺乳动物中，这种选择很弱。其基本原理是，躯干椎体数量的变化需要从躯干到腰椎的同源转换，或者相反，而朝着这种转换的突变通常会产生过渡性的腰椎，这些椎体与骶骨不完全融合。我们假设，这种不完全的同源转换损害了腰椎关节的灵活性，从而威胁到依赖轴向运动获得速度和灵活性的物种的生存。这样的转变只会对缓慢而强壮的物种的表现产生轻微的影响，因此有足够的移行椎骨的个体存活下来，从而最终允许主干椎体数量的进化变化。我们提供了关于快食肉动物、慢食肉动物和偶蹄目动物以及慢速非泡沫动物和单孔目动物的数据，这些数据有力地支持了这一假说。结论是，对主干椎体数量的选择性限制来自于发育和生物力学限制的组合。
The mammalian vertebral column is highly variable, reflecting adaptations to a wide range of lifestyles, from burrowing in moles to flying in bats. However, in many taxa, the number of trunk vertebrae is surprisingly constant. We argue that this constancy results from strong selection against initial changes of these numbers in fast running and agile mammals, whereas such selection is weak in slower-running, sturdier mammals. The rationale is that changes of the number of trunk vertebrae require homeotic transformations from trunk into sacral vertebrae, or vice versa, and mutations toward such transformations generally produce transitional lumbosacral vertebrae that are incompletely fused to the sacrum. We hypothesize that such incomplete homeotic transformations impair flexibility of the lumbosacral joint and thereby threaten survival in species that depend on axial mobility for speed and agility. Such transformations will only marginally affect performance in slow, sturdy species, so that sufficient individuals with transitional vertebrae survive to allow eventual evolutionary changes of trunk vertebral numbers. We present data on fast and slow carnivores and artiodactyls and on slow afrotherians and monotremes that strongly support this hypothesis. The conclusion is that the selective constraints on the count of trunk vertebrae stem from a combination of developmental and biomechanical constraints.