Morphological and molecular diversity of Lake Baikal candonid ostracods, with description of a new genus

Abstract. Uncoupling between molecular and morphological evolution is common in many animal and plant lineages. This is especially frequent among groups living in ancient deep lakes, because these ecosystems promote rapid morphological diversification, and has already been demonstrated for Tanganyika cychlid fishes and Baikal amphipods. Ostracods are also very diverse in these ecosystems, with 107 candonid species described so far from Baikal, majority of them in the genera Candona Baird, 1845 and Pseudocandona Kaufmann, 1900. Here we study their morphological and molecular diversity based on four genes (two nuclear and two mitochondrial), 10 species from the lake, and 28 other species from around the world. The results of our phylogenetic analysis based on a concatenated data set, along with sequence diversity, support only two genetic lineages in the lake and indicate that a majority of the Baikal Candona and Pseudocandona species should be excluded from these genera. We describe a new genus, Mazepovacandona gen. n., to include five Baikal species, all redescribed here. We also amend the diagnosis for the endemic genus Baicalocandona Mazepova, 1972 and redescribe two species. Our study confirms an exceptional morphological diversity of Lake Baikal candonids and shows that both Baikal lineages are closely related to Candona, but only distantly to Pseudocandona.