Marine Evolutionary Ecology, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
Department of Marine and Environmental Sciences, Northeastern University, Boston, Massachusetts, USA.
Mol Ecol. 2019 Jun;28(11):2872-2885. doi: 10.1111/mec.15110. Epub 2019 Jun 23.
Marine species tend to have extensive distributions, which are commonly attributed to the dispersal potential provided by planktonic larvae and the rarity of absolute barriers to dispersal in the ocean. Under this paradigm, the occurrence of marine microendemism without geographic isolation in species with planktonic larvae poses a dilemma. The recently described Maya hamlet (Hypoplectrus maya, Serranidae) is exactly such a case, being endemic to a 50-km segment of the Mesoamerican Barrier Reef System (MBRS). We use whole-genome analysis to infer the demographic history of the Maya hamlet and contrast it with the sympatric and pan-Caribbean black (H. nigricans), barred (H. puella) and butter (H. unicolor) hamlets, as well as the allopatric but phenotypically similar blue hamlet (H. gemma). We show that H. maya is indeed a distinct evolutionary lineage, with genomic signatures of inbreeding and a unique demographic history of continuous decrease in effective population size since it diverged from congeners just ~3,000 generations ago. We suggest that this case of microendemism may be driven by the combination of a narrow ecological niche and restrictive oceanographic conditions in the southern MBRS, which is consistent with the occurrence of an unusually high number of marine microendemics in this region. The restricted distribution of the Maya hamlet, its decline in both census and effective population sizes, and the degradation of its habitat place it at risk of extinction. We conclude that the evolution of marine microendemism can be a fast and dynamic process, with extinction possibly occurring before speciation is complete.
海洋物种往往分布广泛，这通常归因于浮游幼虫提供的扩散潜力和海洋中扩散的绝对障碍的罕见性。在这种模式下，浮游幼虫物种中没有地理隔离的海洋微特有现象的出现带来了一个困境。最近描述的玛雅小镇（Hypoplectrus maya，Serranidae）正是这样一个例子，它是中美洲堡礁系统（MBRS） 50 公里长的一段的特有种。我们使用全基因组分析来推断玛雅小镇的种群历史，并将其与同域分布的、泛加勒比地区的黑（H. nigricans）、条纹（H. puella）和黄油（H.unicolor）小镇，以及非地理隔离但表型相似的蓝（H. gemma）小镇进行对比。我们表明，H. maya 确实是一个独特的进化谱系，具有近亲繁殖的基因组特征，自大约 3000 代前与同属物种分化以来，有效种群大小持续减少，具有独特的种群历史。我们认为，这种微特有现象可能是由狭窄的生态位和南部 MBRS 中限制性的海洋条件共同作用驱动的，这与该地区异常高数量的海洋微特有现象的出现是一致的。玛雅小镇的分布范围有限，其种群数量和有效种群数量都在减少，其栖息地退化，使其面临灭绝的风险。我们得出结论，海洋微特有现象的进化可能是一个快速而动态的过程，在物种形成完成之前，灭绝可能已经发生。
