De Decker Sam, Vanormelingen Pieter, Pinseel Eveline, Sefbom Josefin, Audoor Sien, Sabbe Koen, Vyverman Wim
Laboratory for Protistology and Aquatic Ecology, Department of Biology, Ghent University, Krijgslaan 281-S8, 9000 Gent, Belgium.
Laboratory for Protistology and Aquatic Ecology, Department of Biology, Ghent University, Krijgslaan 281-S8, 9000 Gent, Belgium; Research Department, Botanic Garden Meise, Nieuwelaan 38, 1860 Meise, Belgium.
Protist. 2018 Aug;169(4):569-583. doi: 10.1016/j.protis.2018.05.003. Epub 2018 May 29.
Incomplete reproductive isolation between genetically distinct taxa provides an interesting opportunity for speciation and adaptation studies. This phenomenon is well-described in macro-organisms, but less experimental evidence is available for unicellular eukaryotes. Here, we document the sympatric occurrence of genetically differentiated populations of the pennate model diatom Seminavis robusta in coastal subtidal biofilm communities and show widespread potential for gene flow between them. Based on sequence variation in the plastid-encoded rbcL gene, three distinct clades were identified. Morphological variation between the clades reflected their phylogenetic relationships, with subtle differences in valve morphology in the most distant clade compared to the other two clades, which were indistinguishable. Using a large number of experimental crosses we showed that, although reproductive output was significantly lower compared to the majority of within-clade crosses, approximately 34.5% of the inter-clade crosses resulted in viable and fertile progeny. While the nature of the incomplete reproductive isolation remains unknown, its occurrence in natural diatom populations represents an additional mechanism contributing to population genetic structuring and adaptation and can spur further research into the mechanisms of species divergence and the maintenance of species identity in the presence of gene flow.
遗传上不同的分类群之间不完全的生殖隔离为物种形成和适应性研究提供了一个有趣的机会。这种现象在宏观生物中已有充分描述，但单细胞真核生物的实验证据较少。在这里，我们记录了羽纹硅藻模式种强壮半盘藻（Seminavis robusta）在沿海潮下带生物膜群落中遗传分化种群的同域出现，并表明它们之间存在广泛的基因流动潜力。基于质体编码的rbcL基因的序列变异，鉴定出三个不同的进化枝。进化枝之间的形态变异反映了它们的系统发育关系，与另外两个难以区分的进化枝相比，最远距离的进化枝在瓣膜形态上有细微差异。通过大量的实验杂交，我们发现，尽管与大多数同进化枝杂交相比，生殖产量显著降低，但约34.5%的进化枝间杂交产生了可存活且可育的后代。虽然不完全生殖隔离的本质尚不清楚，但其在天然硅藻种群中的出现代表了一种有助于种群遗传结构和适应性的额外机制，并能推动对物种分化机制以及在基因流动存在的情况下物种身份维持机制的进一步研究。
