Evolution of cave suspension feeding in Protodrilidae (Annelida)
Evolution of cave suspension feeding in Protodrilidae (Annelida)
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原蚓科（Annelida）洞穴悬浮进食的进化
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
K. Worsaae
中科院分区：
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作者：
Alejandro Martínez;Kirsten Kvindebjerg;T. Iliffe;K. Worsaae
Protodrilidae 属于一个谱系，到目前为止，该谱系完全由以沉积物为食、高度适应的间质环节动物组成。除一对前触须外，所有原鸟都缺乏附肢、副足和毛皮；并具有细长的身体，适合通过纤毛运动在沙粒之间滑动。这些特征的第一个例外是 Megadrilus pelagicus n。 sp。栖息于兰萨罗特岛拉科罗纳 (La Corona) 洞穴系统的水柱中。这里通过将体内视频记录和先进显微镜观察与系统发育分析相结合来研究其形态和进化历史。我们的研究揭示了其独特的中上层悬浮摄食行为，这是通过其长纤毛触须与自体背侧纤毛龙骨和数条纵向和横向纤毛带相结合而实现的。系统发育分析恢复了 Megadrilus pelagicus n. sp。嵌套在 Protodrilidae 中，表明其独特特征源自该科。这些特征在与洞穴殖民相关的树拓扑中被追踪。这些性状的演变可以从功能上解释，与家族的祖先沉积物喂养行会相比，中上层悬浮喂养策略的不同需求。这种悬浮摄食策略的起源可能是由于近岸生态系统的部分隔离而有利于该生态系统，仅通过高度多孔的火山地下基岩与海洋相连。这种缝隙连接限制了洞穴中捕食者的数量和湍流，但允许水连续流入携带有机颗粒的系统，当不发生光合作用初级生产且沉积受到限制时，有机颗粒是食物的主要来源。这些条件可能会选择中上层悬浮摄食作为 anchialine 洞穴中最可行的生命策略，这也可能反映了中上层悬浮摄食甲壳类动物和环节动物在 anchialine 洞穴组合中的优势。对于进入洞穴系统的以沉积物为食的祖先谱系的物种，例如环节动物科 Protodrilidae 和 Nerillidae，从间隙栖息地到缝隙栖息地的适应性转变似乎与剧烈的形态变化和物种形成相关。与它们的亲属相比，在这些主要间质谱系中观察到的巨大变化表明与生态适应性相关的替代适应性进化途径与先前提出的关注地质或随机过程的理论相反。
Protodrilidae belongs in a lineage that until now entirely consisted of deposit‐feeding, highly adapted interstitial annelids. Except for a pair of anterior palps, all protodrilids lack appendages, parapodia and chaetae; and have slender bodies adapted to glide between the sand grains by ciliary motion. The first exception to these characteristics is Megadrilus pelagicus n. sp. inhabiting the water column of the anchialine La Corona cave system in Lanzarote. Its morphology and evolutionary history are here investigated by combining observations from in vivo video recordings and advanced microscopy with phylogenetic analyses. Our studies revealed a unique pelagic, suspension feeding behaviour attained by its long ciliated palps in combination with an autopomorphic dorsal ciliated keel and several longitudinal and transverse ciliary bands. Phylogenetic analyses recovered Megadrilus pelagicus n. sp. nested within Protodrilidae indicating that its unique traits are derived within the family. These traits are traced in the tree topologies in correlation to cave colonization. The evolution of these traits can be functionally explained by the different demands of a pelagic suspension feeding strategy compared to the ancestral deposit‐feeding guild of the family. The origin of this suspension feeding strategy was presumably favoured by the partial isolation of the anchialine ecosystem, connected to the sea only through the highly porous volcanic subterranean bedrock. This crevicular connection limits the amount of predators and turbulence in the cave, but allows continuous water flow into the system carrying organic particles, which is the main source of food when photosynthetic primary production does not occur and sedimentation is limited. These conditions may select for pelagic suspension feeding as the most feasible life‐strategy in anchialine caves, which the dominance of pelagic, suspension feeding crustaceans and annelids in anchialine cave assemblages may also reflect. For species of ancestrally deposit‐feeding lineages entering the cave system, such as the annelid families Protodrilidae and Nerillidae, an adaptive‐shift from interstitial to crevicular habitats seemingly correlates with dramatic morphological changes and speciation. The dramatic changes observed in these primarily interstitial lineages compared to their relatives, point to alternative adaptive evolutionary pathways related to ecological fitness contrary to the previously proposed theories focusing on geological or stochastic processes.