Neiva João, Serrão Ester A, Anderson Laura, Raimondi Peter T, Martins Neusa, Gouveia Licínia, Paulino Cristina, Coelho Nelson C, Miller Kathy Ann, Reed Daniel C, Ladah Lydia B, Pearson Gareth A
CCMAR- Centro de Ciências do Mar da Universidade do Algarve, Edifício 7, Gambelas, 8005-139, Faro, Portugal.
Long Marine Laboratory, University of California, Santa Cruz, USA.
BMC Evol Biol. 2017 Jan 23;17(1):30. doi: 10.1186/s12862-017-0878-2.
Molecular markers are revealing a much more diverse and evolutionarily complex picture of marine biodiversity than previously anticipated. Cryptic and/or endemic marine species are continually being found throughout the world oceans, predominantly in inconspicuous tropical groups but also in larger, canopy-forming taxa from well studied temperate regions. Interspecific hybridization has also been found to be prevalent in many marine groups, for instance within dense congeneric assemblages, with introgressive gene-flow being the most common outcome. Here, using a congeneric phylogeographic approach, we investigated two monotypic and geographically complementary sister genera of north-east Pacific intertidal seaweeds (Hesperophycus and Pelvetiopsis), for which preliminary molecular tests revealed unexpected conflicts consistent with unrecognized cryptic diversity and hybridization.
The three recovered mtDNA clades did not match a priori species delimitations. H. californicus was congruent, whereas widespread P. limitata encompassed two additional narrow-endemic species from California - P. arborescens (here genetically confirmed) and P. hybrida sp. nov. The congruence between the genotypic clusters and the mtDNA clades was absolute. Fixed heterozygosity was apparent in a high proportion of loci in P. limitata and P. hybrida, with genetic analyses showing that the latter was composed of both H. californicus and P. arborescens genomes. All four inferred species could be distinguished based on their general morphology.
This study confirmed additional diversity and reticulation within NE Pacific Hesperophycus/Pelvetiopsis, including the validity of the much endangered, modern climatic relict P. arborescens, and the identification of a new, stable allopolyploid species (P. hybrida) with clearly discernable ancestry (♀ H. californicus x ♂ P. arborescens), morphology, and geographical distribution. Allopolyploid speciation is otherwise completely unknown in brown seaweeds, and its unique occurrence within this genus (P. limitata possibly representing a second example) remains enigmatic. The taxonomic separation of Hesperophycus and Pelvetiopsis is not supported and the genera should be synonymized; we retain only the latter. The transitional coastline between Point Conception and Monterey Bay represented a diversity hotspot for the genus and the likely sites of extraordinary evolutionary events of allopolyploid speciation at sympatric range contact zones. This study pinpoints how much diversity (and evolutionary processes) potentially remains undiscovered even on a conspicuous seaweed genus from the well-studied Californian intertidal shores let alone in other, less studied marine groups and regions/depths.
分子标记所揭示的海洋生物多样性图景，比之前预期的要丰富得多，且在进化上更为复杂。世界各地的海洋中不断发现隐存种和/或特有海洋物种，主要集中在不太显眼的热带类群中，但在研究充分的温带地区的大型、形成冠层的分类群中也有发现。种间杂交在许多海洋类群中也很普遍，例如在密集的同属组合中，渐渗基因流是最常见的结果。在这里，我们采用同属系统地理学方法，研究了东北太平洋潮间带海藻的两个单型且地理互补的姐妹属（Hesperophycus和Pelvetiopsis），初步分子测试显示，它们存在与未被识别的隐存多样性和杂交现象一致的意外冲突。
三个恢复的线粒体DNA分支与先验的物种界定不匹配。加州Hesperophycus californicus与之相符，而分布广泛的Pelvetiopsis limitata包含来自加利福尼亚的另外两个窄域特有物种——P. arborescens（此处经基因确认）和新物种P. hybrida。基因型簇与线粒体DNA分支之间完全一致。在P. limitata和P. hybrida的大部分位点中，固定杂合性明显，遗传分析表明后者由H. californicus和P. arborescens的基因组组成。所有四个推断出的物种都可以根据其一般形态区分开来。
本研究证实了东北太平洋Hesperophycus/Pelvetiopsis属内存在更多的多样性和网状进化关系，包括极度濒危的现代气候残遗种P. arborescens的有效性，以及鉴定出一个新的、稳定的异源多倍体物种（P. hybrida），其具有清晰可辨的祖先（♀H. californicus×♂P. arborescens）、形态和地理分布。异源多倍体物种形成在褐藻中完全未知，其在该属内的独特出现（P. limitata可能代表另一个例子）仍然是个谜。不支持将Hesperophycus和Pelvetiopsis进行分类学上的分离，这两个属应同义；我们只保留后者。康塞普申角和蒙特雷湾之间的过渡海岸线是该属的一个多样性热点，也是同域分布接触带异源多倍体物种形成的非凡进化事件的可能发生地点。这项研究指出，即使是来自研究充分的加利福尼亚潮间带海岸的一个显眼的海藻属，仍有多少多样性（和进化过程）可能未被发现，更不用说其他研究较少的海洋类群和区域/深度了。
