Department of Biology, Clark University, Worcester, MA 01610, USA.
Proc Biol Sci. 2020 Mar 25;287(1923):20200192. doi: 10.1098/rspb.2020.0192. Epub 2020 Mar 18.
Dramatic evolutionary transitions in morphology are often assumed to be adaptive in a new habitat. However, these assumptions are rarely tested because such tests require intermediate forms, which are often extinct. In vertebrates, the evolution of an elongate, limbless body is generally hypothesized to facilitate locomotion in fossorial and/or cluttered habitats. However, these hypotheses remain untested because few studies examine the locomotion of species ranging in body form from tetrapod to snake-like. Here, we address these functional hypotheses by testing whether trade-offs exist between locomotion in surface, fossorial and cluttered habitats in Australian lizards, which include multiple intermediate forms. We found that snake-like species penetrated sand substrates faster than more lizard-like species, representing the first direct support of the adaptation to fossoriality hypothesis. By contrast, body form did not affect surface locomotion or locomotion through cluttered leaf litter. Furthermore, all species with hindlimbs used them during both fossorial and surface locomotion. We found no evidence of a trade-off between fossorial and surface locomotion. This may be either because employed kinematic strategies that took advantage of both axial- and limb-based propulsion. This may have led to the differential occupation of their habitat, facilitating diversification of intermediate forms.
形态上戏剧性的进化转变通常被认为是在新栖息地中的适应性。然而，这些假设很少被检验，因为这样的检验需要中间形式，而中间形式通常已经灭绝了。在脊椎动物中，细长的无肢身体的进化通常被假设为在穴居和/或杂乱的栖息地中有利于运动。然而，这些假设仍然未经检验，因为很少有研究检查从四足动物到蛇形的物种在身体形态上的运动。在这里，我们通过测试澳大利亚蜥蜴是否存在在表面、穴居和杂乱的栖息地中运动的权衡来解决这些功能假设，这些蜥蜴包括多种中间形式。我们发现，蛇形物种比更像蜥蜴的物种更快地穿透沙质基质，这代表了对穴居适应性假说的首次直接支持。相比之下，身体形态并不影响表面运动或穿过杂乱的落叶层的运动。此外，所有有后肢的物种在穴居和表面运动中都使用后肢。我们没有发现穴居和表面运动之间存在权衡的证据。这可能是因为它们采用了利用轴和肢体推进的运动学策略。这可能导致了它们栖息地的差异化，促进了中间形式的多样化。
