Genetic data support reproductively isolated species in the endemic Cladophoraceae (Chlorophyta) of Lake Baikal, Russia

© 2020, © 2020 International Phycological Society. Ancient lakes are centres of biological diversification that hold many examples of adaptive radiation and species flocks. The recently discovered species flock of Cladophoraceae in Lake Baikal is a group of green algae that exhibit low genetic divergence in ribosomal markers (LSU, SSU, and ITS), but wide morphological differentiation. Microsatellite markers showed evidence of polyploidy in this group, requiring alternate data scoring methodologies. In this study, we use two clustering methods (STRUCTURE and Gaussian Clustering) to delineate species within 15 distinct morphotaxa of the cladophoralean Baikal clade. The two cluster analyses produced comparable results, although subtle differences in the assignment of individuals were observed. Our results indicate that many morphologically distinguishable species are discrete genetic clusters supporting reproductive isolation. This is the case for Chaetomorpha (= Ch.) baicalensis, the attached form of Ch. curta, Ch. moniliformis, Cladophora (= Cl.) compacta, and Cl. kursanovii. The unattached form of Ch. curta and a species of Rhizoclonium are recovered as growth forms of Ch. moniliformis and the attached form of Ch. curta, respectively. The remaining morphotaxa were not clearly delimited. While we have evidence for polyploidy within this species flock, it was not possible to determine the ploidy level of each individual with accuracy as no correlation in the number of alleles was observed between loci. A more detailed study including other sources of data, such as nuclear DNA content or chromosome counts, is required to demonstrate the ploidy changes and their role in speciation in these species.