Department of Invertebrate Zoology, Smithsonian Institution, National Museum of Natural History, P.O. Box 37012, Washington, DC, USA.
Molecular Ecology Group (MEG), Water Research Institute (IRSA), National Research Council of Italy (CNR), Largo Tonolli, 50, Pallanza, Italy.
Sci Rep. 2021 May 21;11(1):10718. doi: 10.1038/s41598-021-89459-y.
Across Annelida, accessing the water column drives morphological and lifestyle modifications-yet in the primarily "benthic" scale worms, the ecological significance of swimming has largely been ignored. We investigated genetic, morphological and behavioural adaptations associated with swimming across Polynoidae, using mitogenomics and comparative methods. Mitochondrial genomes from cave and pelagic polynoids were highly similar, with non-significant rearrangements only present in cave Gesiella. Gene orders of the new mitogenomes were highly similar to shallow water species, suggestive of an underlying polynoid ground pattern. Being the first phylogenetic analyses to include the holopelagic Drieschia, we recovered this species nested among shallow water terminals, suggesting a shallow water ancestry. Based on these results, our phylogenetic reconstructions showed that swimming evolved independently three times in Polynoidae, involving convergent adaptations in morphology and motility patterns across the deep sea (Branchipolynoe), midwater (Drieschia) and anchialine caves (Pelagomacellicephala and Gesiella). Phylogenetic generalized least-squares (PGLS) analyses showed that holopelagic and anchialine cave species exhibit hypertrophy of the dorsal cirri, yet, these morphological modifications are achieved along different evolutionary pathways, i.e., elongation of the cirrophore versus style. Together, these findings suggest that a water column lifestyle elicits similar morphological adaptations, favouring bodies designed for drifting and sensing.
在环节动物中，进入水柱会驱动形态和生活方式的改变——然而在主要是“底栖”的环节蠕虫中，游泳的生态意义在很大程度上被忽视了。我们使用线粒体基因组学和比较方法研究了游泳相关的遗传、形态和行为适应性，研究对象为 Polynoidae 科。洞穴和海洋 Polynoidae 的线粒体基因组非常相似，只有洞穴 Gesiella 存在非显著重排。新线粒体基因组的基因顺序与浅海物种高度相似，表明存在潜在的 Polynoid 基本模式。作为首次包括全海洋 Drieschia 的系统发育分析，我们发现该物种嵌套在浅海末端，表明其祖先来自浅海。基于这些结果，我们的系统发育重建表明，游泳在 Polynoidae 中独立进化了三次，涉及深海（Branchipolynoe）、中层水（Drieschia）和潮下带洞穴（Pelagomacellicephala 和 Gesiella）中形态和运动模式的趋同适应。系统发育广义最小二乘法（PGLS）分析表明，全海洋和潮下带洞穴物种的背刚毛肥大，但这些形态学的改变是通过不同的进化途径实现的，即刚毛体的伸长和风格。总之，这些发现表明，水柱生活方式会引发类似的形态适应，有利于设计用于漂流和感知的身体。
