Bythinella Moquin-Tandon, 1856 (Gastropoda: Rissooidea: Bythinellidae) in Romania: species richness in a glacial refugium.

Mitochondrial cytochrome oxidase I (COI) and ribosomal internal transcribed spacer 1 (ITS-1) sequences were analysed in 12 Romanian Bythinella populations. Phylogenetic relationships were inferred using maximum parsimony, maximum likelihood and Bayesian techniques. For COI, the Kimura two-parameter (K2P) distances and haplotype networks were computed. Two sympatric and four allopatric groups were distinguished. The K2P distances are similar to those for congeneric rissooids, so each of the six groups represents a species. Two are identified as Bythinella molcsanyi H. Wagner, 1941, and Bythinella dacica Grossu, 1946. The other four groups cannot be ascribed to any known Bythinella. The occurrence of six species, each with a low haplotype number and high interspecific differences between haplotypes, is explained by: (1) a relatively long history of Bythinella in the territory of a Pleistocene glacial refugium; (2) the discontinuous character of the northernmost refugium, promoting speciation, but local extinction and subsequent recolonization; (3) unstable, post-glacial microhabitat conditions; and (4) the fragmented distribution of Romanian Bythinella. [ABSTRACT FROM AUTHOR]