Swift H F, Gómez Daglio L, Dawson M N
School of Natural Sciences, 5200 North Lake Road, University of California, Merced, CA 95343, USA.
Mol Phylogenet Evol. 2016 Jun;99:103-115. doi: 10.1016/j.ympev.2016.02.013. Epub 2016 Mar 8.
Evolutionary inference can be complicated by morphological crypsis, particularly in open marine systems that may rapidly dissipate signals of evolutionary processes. These complications may be alleviated by studying systems with simpler histories and clearer boundaries, such as marine lakes-small bodies of seawater entirely surrounded by land. As an example, we consider the jellyfish Mastigias spp. which occurs in two ecotypes, one in marine lakes and one in coastal oceanic habitats, throughout the Indo-West Pacific (IWP). We tested three evolutionary hypotheses to explain the current distribution of the ecotypes: (H1) the ecotypes originated from an ancient divergence; (H2) the lake ecotype was derived recently from the ocean ecotype during a single divergence event; and (H3) the lake ecotype was derived from multiple, recent, independent, divergences. We collected specimens from 21 locations throughout the IWP, reconstructed multilocus phylogenetic and intraspecific relationships, and measured variation in up to 40 morphological characters. The species tree reveals three reciprocally monophyletic regional clades, two of which contain ocean and lake ecotypes, suggesting repeated, independent evolution of coastal ancestors into marine lake ecotypes, consistent with H3; hypothesis testing and an intraspecific haplotype network analysis of samples from Palau reaffirms this result. Phylogenetic character mapping strongly correlates morphology to environment rather than lineage (r=0.7512, p<0.00001). Considering also the deeper relationships among regional clades, morphological similarity in Mastigias spp. clearly results from three separate patterns of evolution: morphological stasis in ocean medusae, convergence of lake morphology across distinct species and parallelism between lake morphologies within species. That three evolutionary routes each result in crypsis illustrates the challenges of interpreting evolutionary processes from patterns of biogeography and diversity in the seas. Identifying cryptic species is only the first step in understanding these processes; an equally important second step is exploring and understanding the processes and patterns that create crypsis.
进化推断可能会因形态隐匿而变得复杂，尤其是在开放的海洋系统中，这些系统可能会迅速消散进化过程的信号。通过研究历史更简单、边界更清晰的系统，例如海湖——完全被陆地包围的小型海水水体，这些复杂性可能会得到缓解。作为一个例子，我们考虑了水母 Mastigias spp.，它在整个印度-西太平洋地区（IWP）以两种生态型出现，一种在海湖，另一种在沿海海洋栖息地。我们测试了三个进化假说来解释当前生态型的分布：（H1）生态型起源于古老的分化；（H2）湖生态型是在一次单一的分化事件中最近从海洋生态型衍生而来；以及（H3）湖生态型是由多个近期的、独立的分化衍生而来。我们从IWP的21个地点收集了标本，重建了多位点系统发育和种内关系，并测量了多达40个形态特征的变异。物种树揭示了三个相互单系的区域分支，其中两个包含海洋和湖生态型，这表明沿海祖先反复独立进化为海湖生态型，与H3一致；对来自帕劳的样本进行的假设检验和种内单倍型网络分析再次证实了这一结果。系统发育特征映射强烈表明形态与环境而非谱系相关（r = 0.7512，p < 0.00001）。考虑到区域分支之间更深层次的关系，Mastigias spp. 的形态相似性显然源于三种不同的进化模式：海洋水母的形态停滞、不同物种间湖形态的趋同以及物种内湖形态之间的平行进化。这三条进化路线都导致了隐匿现象，说明了从海洋生物地理学和多样性模式解释进化过程的挑战。识别隐性物种只是理解这些过程的第一步；同样重要的第二步是探索和理解产生隐匿现象的过程和模式。
