Department of Biology, Lund University, 223 62, Lund, Sweden.
Institute of Cytology of the Russian Academy of Science, Tikhoretsky Avenue 4, St. Petersburg, 194064, Russia.
Sci Rep. 2024 Feb 29;14(1):4986. doi: 10.1038/s41598-024-55362-5.
Protists make up the vast diversity of eukaryotic life and play a critical role in biogeochemical cycling and in food webs. Because of their small size, cryptic life cycles, and large population sizes, our understanding of speciation in these organisms is very limited. We performed population genomic analyses on 153 strains isolated from eight populations of the recently radiated dinoflagellate genus Apocalathium, to explore the drivers and mechanisms of speciation processes. Species of this genus inhabit both freshwater and saline habitats, lakes and seas, and are found in cold temperate environments across the world. RAD sequencing analyses revealed that the populations were overall highly differentiated, but morphological similarity was not congruent with genetic similarity. While geographic isolation was to some extent coupled to genetic distance, this pattern was not consistent. Instead, we found evidence that the environment, specifically salinity, is a major factor in driving ecological speciation in Apocalathium. While saline populations were unique in loci coupled to genes involved in osmoregulation, freshwater populations appear to lack these. Our study highlights that adaptation to freshwater through loss of osmoregulatory genes may be an important speciation mechanism in free-living aquatic protists.
原生生物构成了真核生物多样性的主体，在生物地球化学循环和食物网中起着关键作用。由于它们体积小、生命周期隐蔽以及种群数量庞大，我们对这些生物的物种形成的理解非常有限。我们对 153 株从 8 个新近辐射的腰鞭毛目属 Apocalathium 种群中分离出的菌株进行了群体基因组分析，以探讨物种形成过程的驱动因素和机制。该属的物种栖息于淡水和咸水栖息地、湖泊和海洋，在世界各地的冷温带环境中都有发现。RAD 测序分析表明，这些种群总体上高度分化，但形态相似性与遗传相似性并不一致。虽然地理隔离在一定程度上与遗传距离相关，但这种模式并不一致。相反，我们发现证据表明，环境，特别是盐度，是 Apocalathium 生态物种形成的主要因素。虽然盐生种群在与参与渗透调节的基因相关的基因座上是独特的，但淡水种群似乎缺乏这些基因座。我们的研究表明，通过失去渗透调节基因适应淡水可能是自由生活水生原生生物物种形成的一个重要机制。
