Studies On Molecular Phylogeny Of Parasitic Unionicolid Mites (Acari: Unionicolidae: Unionicola) Based On Mitochondrial COI And Ribosmal ITS2 Gene

Parasitic unionicolid mites are a group of water mites which living in freshwater; there are several parasitic unionicoild mites in China, such as U. arcuata,U. ypsilophora,U. chelata,U. agilex and so on, they are the mainly parasites in freshwater bivalves. Morphological differences among species of parasitic unionicolid mites are comparatively minor, with taxonomic distinctions among most members of the taxon based on subtle differences in one or two morphological characters. In addition, because of their high productivity, short generation cycle, fast development progress and they can coevolution with their host that result in morphological differences, so in systematics, there exist a lots of argument on parasitic unionicolid mites' taxon.In the present study, partial sequences of mitochondrial DNA COI gene and ribosomal DNA ITS2 gene of seventeen samples including five species of parasitic unionicolid mites in the freshwater bivalves and a free-living Unionicola crassipes were sequenced, these water mites were collected from the main lakes (Poyang Lake,Dongting Lake,Taihu Lake,Chaohu Lake,Honghu Lake) on the low and middle reaches of the Yangtze River. All these COI and ITS2 sequences data were used to analyze the phylogenetic relationship of parasitic unionicolid mites. The major achievements of this paper were as follows:1. From the sequence analysis of COI gene, The relationship between U. chelata and U. arcuata was the farthest among all the parasitic unionicolid mites, the relationship between U. ischyropalpus and U. arcuata was the closest. from the phylogenetic trees, we can see that U. arcuata was relatively evolutionary species and U. agilex sp. nov. was relatively original species.2. From the sequence analysis of ITS2 gene, The relationship between U. agilex and U. ischyropalpus was the farthest among all the parasitic unionicolid mites, the relationship between U. ischyropalpus and U. chelata was the closest. from the phylogenetic trees, we can see that U. arcuata was relatively evolutionary species and U. ypsilophora was relatively original species.3. Combining the two molecular markers, we can find that their nucleotide sequences were rich in A and T. the main lakes on the low and middle reaches of the Yangtze River had little effect on the genetic structure of parasitic unionicolid mites, and host specificity was the mian reason of genetic diversity. U. arcuata was relatively evolutionary species, respecting the relatively original species and their relationship were indefinite in both COI gene and ITS2 gene, it needs to combine the molecular marker with morphological identification, this is also the necessary path to solve the puzzle of species' taxon and identification.