| Summary: | <p>Abstract</p> <p>Background</p> <p>Two colour forms of the two-spotted spider mite (<it>Tetranychus urticae </it>Koch) coexist in China: a red (carmine) form, which is considered to be native and a green form which is considered to be invasive. The population genetic diversity and population genetic structure of this organism were unclear in China, and there is a controversy over whether they constitute distinct species. To address these issues, we genotyped a total of 1,055 individuals from 18 red populations and 7 green populations in China using eight microsatellite loci.</p> <p>Results</p> <p>We identified 109 alleles. We found a highly significant genetic differentiation among the 25 populations (global <it>F</it><sub>ST </sub>= 0.506, global <it>F</it><sub>ST </sub><sup>{<it>ENA</it>} </sup>= 0.473) and a low genetic diversity in each population. In addition, genetic diversity of the red form mites was found to be higher than the green form. Pearson correlations between statistics of variation (<it>AR </it>and <it>H</it><sub>E</sub>) and geographic coordinates (latitude and longitude) showed that the genetic diversity of the red form was correlated with latitude. Using Bayesian clustering, we divided the Chinese mite populations into five clades which were well congruent with their geographic distributions.</p> <p>Conclusions</p> <p>Spider mites possess low levels of genetic diversity, limit gene flow between populations and significant and IBD (isolation by distance) effect. These factors in turn contribute to the strong subdivision of genetic structure. In addition, population genetic structure results don't support the separation of the two forms of spider mite into two species. The morphological differences between the two forms of mites may be a result of epigenetic effects.</p>
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