Rapid diversification of a free-living protist is driven by adaptation to climate and habitat.

Microbial eukaryotes (protists) have major functional roles in aquatic ecosystems, including the biogeochemical cycling of elements as well as occupying various roles in the food web. Despite their importance for ecosystem function, the factors that drive diversification in protists are not known. Here, we aimed to identify the factors that drive differentiation and, subsequently, speciation in a free-living protist, Synura petersenii (Chrysophyceae). We sampled five different geographic areas and utilized population genomics and quantitative trait analyses. Habitat and climate were the major drivers of diversification on the local geographical scale, while geography played a role over longer distances. In addition to conductivity and temperature, precipitation was one of the most important environmental drivers of differentiation. Our results imply that flushing episodes (floods) drive microalgal adaptation to different niches, highlighting the potential for rapid diversification in protists.

When you Like Other Algae: Adglutina synurophila gen. et sp. nov. (Moewusinia, Chlorophyceae), a Clingy Green Microalga Associated with Synura Colonies.

Unicellular green biflagellates of the order Volvocales (Chlorophyceae, Chlorophyta) are common inhabitants of various types of habitats, and can also form peculiar interspecific relationships. Most of their morphological diversity has historically been assigned to the two prominent genera Chlamydomonas and Chloromonas. Ongoing reclassification of these algae, aided by molecular phylogenetics, has resulted in numerous newly proposed genera, but there are certainly brand-new taxa awaiting recognition. In this study, based on morphological and ultrastructural observations together with sequence data of the nuclear 18S and ITS2 rDNA and the plastid rbcL gene, we describe Adglutina synurophila gen. et sp. nov., a volvocalean biflagellate isolated from colonies of the golden-brown alga Synura petersenii (Chrysophyceae). Phylogenetic analyses placed Adglutina in the phylogroup Moewusinia as a sister lineage to the acidophilic "Chlamydomonas" species. It is characterised by having oval to broadly ellipsoidal cells with a low keel-shaped papilla and a cup-shaped chloroplast lacking a pyrenoid, but possessing a lateral eyespot of a variable position. The unique set of features, together with its Synura-loving nature, anchor Adglutina as a well distinguishable phylogenetic lineage within the Moewusinia. The novel alga has a widespread distribution; it has been found in three European countries to date.

Comparing Morphological and Molecular Estimates of Species Diversity in the Freshwater Genus Synura (Stramenopiles): A Model for Understanding Diversity of Eukaryotic Microorganisms.

We performed a comparison of molecular and morphological diversity in a freshwater colonial genus Synura (Chrysophyceae, Stramenopiles), using the island of Newfoundland (Canada) as a case study. We examined the morphological species diversity in collections from 79 localities, and compared these findings to diversity based on molecular characters for 150 strains isolated from the same sites. Of 27 species or species-level lineages identified, only one third was recorded by both molecular and morphological techniques, showing both approaches are complementary in estimating species diversity within this genus. Eight taxa, each representing young evolutionary lineages, were recovered only by sequencing of isolated colonies, whereas ten species were recovered only microscopically. Our complex investigation, involving both morphological and molecular examinations, indicates that our knowledge of Synura diversity is still poor, limited only to a few well-studied areas. We revealed considerable cryptic diversity within the core S. petersenii and S. leptorrhabda lineages. We further resolved the phylogenetic position of two previously described taxa, S. kristiansenii and S. petersenii f. praefracta, propose species-level status for S. petersenii f. praefracta, and describe three new species, S. vinlandica, S. fluviatilis, and S. cornuta. Our findings add to the growing body of literature detailing distribution patterns observed in the genus, ranging from cosmopolitan species, to highly restricted taxa, to species such as S. hibernica found along coastal regions on multiple continents. Finally, our study illustrates the usefulness of combining detailed morphological information with gene sequence data to examine species diversity within chrysophyte algae.