[Polymorphism of the cox1 gene in bird schistosome cercaria isolates (Trematoda, Schistosomatidae) from ponds of Moscow and Moscow oblast].

Polymorphism of a 8 10-bp mitochondrial cox1 gene region was studied in 16 cercaria isolates of bird schistosomes (family Schistosomatidae), which were collected in water bodies of Moscow and Moscow oblast and represented three species: Trichobilharzia szidati, T. franki, and T. regenti. A substantial predominance of AT (65.4%) was characteristic of the cox1 sequences in all three species. Rare single nucleotide substitutions determined low (0.2-0.9%) intraspecific nucleotide and amino acid sequence diversity. Haplotype diversity h was high (80-100%) in all three species, suggesting a unique character for almost all cox1 sequences in the sample. Phylogenetic trees based on the nucleotide and amino acid sequence variations were constructed to study the relationships of the three schistosome species. A high support was observed for the main branching node that reflects differentiation of the monophyletic group Trichobilharzia and species of the genera Bilharziella (B. polonica), Dendritobilharzia (D. pulverulenta), and Gigantobilharzia (G. huronensis). Based on the nucleotide substitutions and amino acid polymorphisms, two groups of isolates, which infect Lymnaea stagnalis (T. szidati) and snails of the group Radix (T. franki and T. regenti) respectively, were isolated in the genus Trichobilharzia. The time of divergence between the two schistosome groups infecting snails of the genera Radix and Lymnaea was calculated from the cox1 nucleotide substitution rate, which is known for Asian and Indian blood flukes from the genus Schistosoma and is 2-3% per million years on average. Divergence of the three bird schistosome species under study and divergence of the Asian species of mammalian schistosome were almost concurrent, dating back to 2.5-3.8 Myr ago. Factors responsible for the lack of intraspecific subdivision with respect to the cox1 gene in bird schistosomes and the lack of separation between two species (T. franki and T. regenti) are discussed.