Terrestriality constrains salamander limb diversification: Implications for the evolution of pentadactyly
Terrestriality constrains salamander limb diversification: Implications for the evolution of pentadactyly
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DOI：
10.1111/jeb.13444
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发表时间：
2019-04
影响因子：
2.1
通讯作者：
Nicholus M Ledbetter;R. Bonett
中科院分区：
文献类型：
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作者：
Nicholus M Ledbetter;R. Bonett
当物种在适应区之间移动时，表型进化的模式会突然改变。现存的蝾螈显示出三种不同的生命周期策略，从水生到陆生（双相），完全水生（幼态）和完全陆生（直接发展）。生命周期变异与身体形态的变化有关，如失去手指、肢体减少或身体伸长。然而，这些特征与生命周期策略之间的关系仍然没有得到解决。在这里，我们使用贝叶斯建模方法来测试蝾螈的生命周期转换是否影响率，最优和整合的主要运动结构（四肢和躯干）。我们发现，幼态蝾螈有肢体进化的最优移向更小的尺寸和更少的数字相比，所有其他蝾螈提高率。率后肢数字的进化表明，在梯度下降的生命周期变得更加陆地。幼形动物的后肢趾缺失与椎骨数量增加之间的相关性较高，肢体长度之间的相关性也较低。我们的研究结果支持这样的想法，即陆生的跖行运动限制肢体的进化，当解除，导致更高的速度的性状多样化和最优和整合的转变。大多数蝾螈的基本四足动物的身体形式和陆地生命阶段的独立损失提供了一个重要的框架，以了解生态区的重大转变背后的进化和发展机制，如早期四足动物从水到陆地的过渡。
Patterns of phenotypic evolution can abruptly shift as species move between adaptive zones. Extant salamanders display three distinct life cycle strategies that range from aquatic to terrestrial (biphasic), to fully aquatic (paedomorphic) and to fully terrestrial (direct development). Life cycle variation is associated with changes in body form such as loss of digits, limb reduction or body elongation. However, the relationships among these traits and life cycle strategy remain unresolved. Here, we use a Bayesian modelling approach to test whether life cycle transitions by salamanders have influenced rates, optima and integration of primary locomotory structures (limbs and trunk). We show that paedomorphic salamanders have elevated rates of limb evolution with optima shifted towards smaller size and fewer digits compared to all other salamanders. Rate of hindlimb digit evolution is shown to decrease in a gradient as life cycles become more terrestrial. Paedomorphs have a higher correlation between hindlimb digit loss and increases in vertebral number, as well as reduced correlations between limb lengths. Our results support the idea that terrestrial plantigrade locomotion constrains limb evolution and, when lifted, leads to higher rates of trait diversification and shifts in optima and integration. The basic tetrapod body form of most salamanders and the independent losses of terrestrial life stages provide an important framework for understanding the evolutionary and developmental mechanisms behind major shifts in ecological zones as seen among early tetrapods during their transition from water to land.