The endemic Cladophorales (Ulvophyceae) of ancient Lake Baikal represent a monophyletic group of very closely related but morphologically diverse species

Abstract

Lake Baikal, the oldest lake in the world, is home to spectacular biodiversity and extraordinary levels of endemism. While many of the animal species flocks from Lake Baikal are famous examples of evolutionary radiations, the lake also includes a wide diversity of endemic algae that are not well investigated with regards to molecular-biological taxonomy and phylogeny. The endemic taxa of the green algal order Cladophorales show a range of divergent morphologies that led to their classification in four genera in two families. We sequenced partial large- and small-subunit rDNA as well as the internal transcribed spacer region of 14 of the 16 described endemic taxa to clarify their phylogenetic relationships. One endemic morphospecies, Cladophora kusnetzowii, was shown to be conspecific with the widespread Aegagropila linnaei. All other endemic morphospecies formed a monophyletic group nested within the genus Rhizoclonium (Cladophoraceae), a very surprising result, in stark contrast to their morphological affinities. The Baikal clade represents a species flock of closely related taxa with very low genetic differentiation. Some of the morphospecies were congruent with lineages recovered in the phylogenies, but due to the low phylogenetic signal in the rDNA sequences the relationships within the Baikal clade were not all well resolved. The Baikal clade appears to represent a recent radiation, based on the low molecular divergence within the group, and it is hypothesized that the large morphological variation results from diversification in sympatry from a common ancestor in Lake Baikal.

Microsatellite design for species delimitation and insights into ploidy for the Lake Baikal Cladophoraceae species flock

“…Schön & Martens 2012;Sherbakov 1999;Yokoyama & Goto 2005). However, studies on the ecology, evolution, and speciation of the algal flora are limited (for example, see Boedeker et al 2018;Kulikovskiy et al 2012;Volkova et al 2018).…”

“…Among the algae of Lake Baikal, the family Cladophoraceae is highly represented (Boedeker et al 2018;Izhboldina 2007). The family Cladophoraceae is a cosmopolitan group of algae that can be found in fresh, brackish, and marine waters.…”

“…); the abundantly branched Cladophora Kützing (= Cl. ); and the diminutive Gemmiphora Skabichevsky (= G.) (Boedeker et al 2018;Izhboldina 2007). However, recent molecular studies (Boedeker et al 2018) using nuclear ribosomal markers (SSU, LSU, and ITS) revealed that the endemic Baikalian Cladophoraceae are actually a monophyletic group with low genetic differentiation having a maximum of 2.8% pairwise differences in the ITS region (Boedeker et al 2018).…”

“…); and the diminutive Gemmiphora Skabichevsky (= G.) (Boedeker et al 2018;Izhboldina 2007). However, recent molecular studies (Boedeker et al 2018) using nuclear ribosomal markers (SSU, LSU, and ITS) revealed that the endemic Baikalian Cladophoraceae are actually a monophyletic group with low genetic differentiation having a maximum of 2.8% pairwise differences in the ITS region (Boedeker et al 2018). These phylogenies also showed that this clade is nested within Rhizoclonium Kützing, a genus which shows little morphological differentiation (simple unbranched or sparsely branched filaments), but high genetic diversity (Boedeker et al 2018).…”

“…However, recent molecular studies (Boedeker et al 2018) using nuclear ribosomal markers (SSU, LSU, and ITS) revealed that the endemic Baikalian Cladophoraceae are actually a monophyletic group with low genetic differentiation having a maximum of 2.8% pairwise differences in the ITS region (Boedeker et al 2018). These phylogenies also showed that this clade is nested within Rhizoclonium Kützing, a genus which shows little morphological differentiation (simple unbranched or sparsely branched filaments), but high genetic diversity (Boedeker et al 2018). The phylogenetic signal of the ribosomal markers differentiated the Baikalian Cladophorales into two major clades (A and B; Table S1), but lacked support for many other clades and showed little or no genetic difference between some morphospecies.…”