Department of Evolution, Ecology and Organismal Biology, The Ohio State University, Columbus, OH, USA.
Division of Invertebrate Zoology, American Museum of Natural History, New York, NY, USA.
Mol Ecol. 2019 Aug;28(15):3572-3586. doi: 10.1111/mec.15157. Epub 2019 Aug 5.
Sympatric diversification is recognized to have played an important role in the evolution of biodiversity. However, an in situ sympatric origin for codistributed taxa is difficult to demonstrate because different evolutionary processes can lead to similar biogeographic outcomes, especially in ecosystems that can readily facilitate secondary contact due to a lack of hard barriers to dispersal. Here we use a genomic (ddRADseq), model-based approach to delimit a species complex of tropical sea anemones that are codistributed on coral reefs throughout the Tropical Western Atlantic. We use coalescent simulations in fastsimcoal2 and ordinary differential equations in Moments to test competing diversification scenarios that span the allopatric-sympatric continuum. Our results suggest that the corkscrew sea anemone Bartholomea annulata is a cryptic species complex whose members are codistributed throughout their range. Simulation and model selection analyses from both approaches suggest these lineages experienced historical and contemporary gene flow, supporting a sympatric origin, but an alternative secondary contact model receives appreciable model support in fastsimcoal2. Leveraging the genome of the closely related Exaiptasia diaphana, we identify five loci under divergent selection between cryptic B. annulata lineages that fall within mRNA transcripts or CDS regions. Our study provides a rare empirical, genomic example of sympatric speciation in a tropical anthozoan and the first range-wide molecular study of a tropical sea anemone, underscoring that anemone diversity is under-described in the tropics, and highlighting the need for additional systematic studies into these ecologically and economically important species.
同域多样化被认为在生物多样性的进化中发挥了重要作用。然而，由于不同的进化过程可能导致相似的生物地理结果，因此很难证明同域分布的分类群具有原地同域起源，尤其是在那些由于缺乏扩散的硬性障碍而容易促进二次接触的生态系统中。在这里，我们使用基于基因组（ddRADseq）的模型方法来划定热带海葵的一个物种复合体，这些海葵在整个热带西大西洋的珊瑚礁上共同分布。我们使用 coalescent simulations in fastsimcoal2 和 Moments 中的 ordinary differential equations 来测试跨越异域-同域连续体的竞争进化情景。我们的结果表明，螺旋海葵 Bartholomea annulata 是一个隐生种复合体，其成员在其分布范围内共同分布。两种方法的模拟和模型选择分析都表明，这些谱系经历了历史和当代的基因流，支持同域起源，但 fastsimcoal2 中的替代二次接触模型得到了相当的模型支持。利用密切相关的 Exaiptasia diaphana 的基因组，我们在隐生 B. annulata 谱系之间识别出五个在 mRNA 转录本或 CDS 区域内经历分歧选择的位点。我们的研究提供了一个罕见的热带刺胞动物同域物种形成的实证、基因组案例，也是第一个关于热带海葵的全范围分子研究，突出表明在热带地区海葵的多样性被低估了，并强调需要对这些具有生态和经济重要性的物种进行更多的系统研究。
