Heterochronic Shifts Mediate Ecomorphological Convergence in Skull Shape of Microcephalic Sea Snakes
Heterochronic Shifts Mediate Ecomorphological Convergence in Skull Shape of Microcephalic Sea Snakes
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异时性转变介导小头海蛇头骨形状的生态形态趋同
DOI：
10.1093/icb/icz033
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发表时间：
2019
影响因子：
2.6
通讯作者：
Palci, Alessandro
中科院分区：
文献类型：
--
作者：
Sherratt, Emma;Sanders, Kate L;Watson, Amy;Hutchinson, Mark N;Lee, Michael S;Palci, Alessandro
胎生海蛇（水螅蛇科）是一种完全水生的蛇类，其形态上的变化包括一种极端的“小头”型生物，它的头很小，前体很窄，而后体却很厚（可达前体周长的三倍）。先前的研究已经证明，这种形态已经进化了至少9次，这是穴居鳗鱼饮食特殊化的结果，并且还研究了这种身体形状背后的脊柱的形态变化。这项研究要解决的问题是，在这种极端的进化变化中，头骨发生了什么？在这里，我们使用x射线微计算机断层扫描和几何形态测量方法来表征30种海蛇的颅骨形状变化。我们研究了颅骨形状多样性的个体发生和进化模式，以了解颅骨形状是否由饮食专业化预测，并研究小头畸形物种的颅骨形状是否可能是异慢性过程的结果。我们表明，小头畸形物种的小颅骨尺寸具有收敛形状，这与对穴居猎物的营养特化有关。此外，它们的头骨形状可以预测它们的大小，与近亲但非小头型海蛇的幼年个体非常相似。我们的研究结果表明，异慢性变化（导致畸形）驱动了海蛇的头骨形状趋同，以响应饮食特殊化。
Morphological variation among the viviparous sea snakes (Hydrophiinae), a clade of fully aquatic elapid snakes, includes an extreme “microcephalic” ecomorph that has a very small head atop a narrow forebody, while the hind body is much thicker (up to three times the forebody girth). Previous research has demonstrated that this morphology has evolved at least nine times as a consequence of dietary specialization on burrowing eels, and has also examined morphological changes to the vertebral column underlying this body shape. The question addressed in this study is what happens to the skull during this extreme evolutionary change? Here we use X-ray micro-computed tomography and geometric morphometric methods to characterize cranial shape variation in 30 species of sea snakes. We investigate ontogenetic and evolutionary patterns of cranial shape diversity to understand whether cranial shape is predicted by dietary specialization, and examine whether cranial shape of microcephalic species may be a result of heterochronic processes. We show that the diminutive cranial size of microcephalic species has a convergent shape that is correlated with trophic specialization to burrowing prey. Furthermore, their cranial shape is predictable for their size and very similar to that of juvenile individuals of closely related but non-microcephalic sea snakes. Our findings suggest that heterochronic changes (resulting in pedomorphosis) have driven cranial shape convergence in response to dietary specializations in sea snakes.