Wen's Spine A Bear Worm (Tardigrada) Cryptic Species Complex Classification Studied

Cryptic species is one of two or more morphologically indistinguishable biological groups which satisfy the biological definition of species, that is, they are incapable of interbreeding. A cryptic species complex is a group of species, with the increasingly wide application of DNA analysis, more and more kinds of cryptic species complex was found. Usually,cryptic species complexes of individual species can be distinguished by a multi-source information analysis, such as DNA sequence comparisons and observation of life history. cryptic species complexes may be consist of the neighbors groups which are sympatric or allopatric. Gene flow in each species of cryptic species complexes is interrupted, however, the evolution has not reached the degree that morphological of cryptic species complexes can not be easy identifiable. In the research of organism diversity, With the application of DNA sequences (the phylogeography DNA barcodes) increasing, Many cryptic species complexes has been found in all habitats. Currently, the evidence from the identification of cryptic species make people aware that the assessment of species richness is too low on Earth..The cryptic species in Echiniscus wendti, a common species of tardigrade,but few people study it.Cryptic species is one of two or more morphologically indistinguishable biological groups which satisfy the biological definition of species, that is, they are incapable of interbreeding. The cryptic species are considered quite common in tardigrade. However, very few studies on cryptic species in tardigrade were reported. Tardigrades, hydrophilous micrometazoans commonly called "water bears", are generally considered to be an independent phylum. They could be found in permanent freshwater habitats, in sea, river or lake sediment, in littoral zone or in moist mosses. A change in environmental conditions can induce the animal to enter a cryptobiosis, which can be anhydrobiosis, anoxybiosis, cryobiosis or osmobiosis. Cryobiosis enables tardigrades to survive freezing and thawing, and is the principal survival strategy of limno-terrestrial tardigrades living in very cold environments. The formation of tuns also plays a role in the dispersal of cryobiotes. The tardigrade Echiniscus wendti Richters1903is one of the most common species worldwide. The known localities of this species in China include Inner Mongolia, the Tsinling Mountains and the Yunnan-Guizhou Plateau. The present study aims to examine if E. wendti contains any cryptic species. The sampling locations covered only central China including the Tsinling Mountains, the Bashan Mountains, the Taihang Mountains and the Luliang Mountains. The cryptic species was detected using the mitochondrial DNA gene cytochrome oxidase subunit1(COI) as molecular marker in present study. The number of the sample are satify with statistical requirements,it contains10-20sample. The cryptic species was detected using the mitochondrial DNA gene cytochrome oxidase subunit1(COI) as molecular marker in present study. In this study,chloroform isoamy-alcohol extraction method was used to get tardigrade’s DNA, Using the PCR amplification and sequencing method, we succeed to get mitochondrial DNA gene cytochrome oxidase subunit1(COI) sequence just as E. wendti. In which80individual have been uploaded to Genbank, and accession numbers are given in the paper. Results from phylogenetic relationships among haplotypes, genetic structure and the automatic barcode gap discovery (ABGD) analysis together indicated existence of two cryptic species in E. wendti from central China. In addition, significant genetic structure and phylogeographic structure were detected in this species. Three putative genetic barriers were predicted, the latter two of which respectively correspond to the Yellow River and the Han River. Mantel test denied existence of isolation by distance, which probably resulted from the dispersal pattern in tardigrades. Tardigrade could be dispersed for long distance by wind. Analysis of mismatch distribution and neutrality tests rejected sudden population expansion in the total population of E. wendti. It could be concluded that the genetic structure of E. wendti was determined by both the genetic barrier and wind which plays an important role in dispersal of tardigrades.