Data from: Independent origins of parasitism in Animalia

Nearly half of all animals may have a parasitic lifestyle, yet the number of transitions to parasitism and their potential for species diversification remain unresolved. Based on a comprehensive survey of the animal kingdom, we find that parasitism has independently evolved at least 223 times in just 15 phyla, with the majority of identified independent parasitic groups occurring in the Arthropoda, at or below the level of Family. Metazoan parasitology is dominated by the study of helminthes; however, only 20% of independently derived parasite taxa belong to those groups, with numerous transitions also seen in Mollusca, Rotifera, Annelida and Cnidaria. Parasitism is almost entirely absent from deuterostomes, and although worm-like morphology and host associations are widespread across Animalia, the dual symbiotic and trophic interactions required for parasitism may constrain its evolution from antecedent consumer strategies such as generalist predators and filter feeders. In general, parasitic groups do not differ from their free-living relatives in their potential for speciation. However, the 10 largest parasitic clades contain 90% of described parasitic species, or perhaps 40% of all animal species. Hence, a substantial fraction of animal diversity on the Earth arose following these few transitions to a parasitic trophic strategy.现有研究显示，近半数动物类群可能具有寄生生活方式，但学界对动物向寄生生活的演化过渡次数及其驱动物种多样化的潜力仍未得到明确解析。基于对动物界的全面系统性调研，本研究发现寄生现象至少在15个门（phyla）中独立演化了223次，其中已确认的独立寄生类群绝大多数集中于节肢动物门（Arthropoda），且类群等级多为科（Family）或更低阶元。后生动物寄生虫学（Metazoan parasitology）的研究长期以蠕虫类（helminthes）为核心，但仅20%的独立起源寄生类群隶属于此类群；在软体动物门（Mollusca）、轮形动物门（Rotifera）、环节动物门（Annelida）以及刺胞动物门（Cnidaria）中，也存在大量寄生演化过渡事件。寄生现象几乎完全不存在于后口动物（deuterostomes）类群中：尽管蠕虫状形态与宿主关联在动物界中广泛分布，但寄生所需的双重共生与营养相互作用，可能会限制其从广食性捕食者、滤食者等祖先消费策略演化而来的可能性。总体而言，寄生类群与其自由生活的近缘类群在物种形成（speciation）潜力上并无显著差异。然而，10个最大的寄生演化支（clades）涵盖了已描述寄生物种的90%，或许占所有动物物种的40%。因此，地球上相当一部分动物多样性，正是源自这为数不多的几次向寄生营养策略的演化过渡。