基于线粒体基因研究我国痒螨的种群遗传结构

The Psoroptes mite is a common ectoparasite in domestic and wild animals and can cause considerable economic losses in breeding industry and severe survival threats in wild animals. Due to the poor performances of morphology (easily influenced by environmental factors) and molecular markers reported (lack of efficient genetic sites) in Psoroptes mite, until now there has been considerable discussion as to the classification of Psoroptes species. Therefore, more efficient molecular markers with more genetic information are needed urgently. The mt genome (mtDNA) contains many useful markers, and these markers are widely used for the resolution of taxonomic discrepancies between closely related species. However, no any information on the mtDNA of Prosoptes mites was previously available. Meanwhile, limited information involved to the population genetic structure and gene flow of Psoroptes spp. was also uncovered recently. Here, we will first determine the complete mtDNA of representatives of Psorotes mites from sheep, buffalo, and rabbits and reconstructed phylogeny of Psorotes spp. in Acariformes using mtDNA data. Additionally, Based on comparative mitogenomics performed among Acariformes species, the new molecular marker genes are identified and screened for mite classifications at different taxonomic levels. Finally, several targeted mt genes were used as new molecular markers for constructing evolutionary trees and revealing genetic distances, genetic diversity, gene flows, and genetic relationships in Psoroptes isolates from six sampling areas in China. These results should provide new insights into the genetic structure and classification of the Psoroptes populations in China, and lay the theoretical foundation for cure, diagnose, and prevention of psoroptic mange.

痒螨是寄生于各种家养及野生动物体表的常见外寄生虫之一，对养殖业造成重大经济损失，同时也威胁野生动物的生存。由于形态学（易受环境等的影响）和现有的分子标记（缺乏有效的遗传信息位点）在分类上的局限，至今痒螨的分类结果仍颇具争议，因此急需寻求新的分子标记。线粒体基因组包含了众多的分子标记，已被广泛用于解决近缘物种的分类。鉴于目前痒螨的线粒体基因组及其种群遗传结构和基因流的研究尚未见报道。本研究欲在获得绵羊、水牛和兔的痒螨虫株线粒体全基因组序列基础之上，运用生物信息学构建进化树阐明真螨总目内的系统发生关系；通过比较基因组学从线粒体基因组筛选出不同分类阶元的分子标记，在采集我国6大区域的痒螨虫株基础上，获得相应基因序列，进而构建进化树并分析痒螨各类群间和类群内的遗传距离、遗传多样性、基因流水平、亲缘关系，揭示我国痒螨群体遗传结构特征及分类，为痒螨病的治疗、诊断以及预防奠定理论依据。

痒螨是各种家养及野生动物体表的常见外寄生虫之一，对养殖业造成重大经济损失，同时威胁野生动物的生存。目前痒螨的线粒体基因组（mtDNA）及其种群遗传结构的研究未见报道。本研究首先利用PCR分段扩增与引物步移方法获得绵羊痒螨兔亚种的mtDNA并进行注释，然后以12个蛋白编码基因（atp8除外）的氨基酸序列为源数据构建蜱螨亚纲（Acari）的系统进化关系。其次，通过比较基因组学从获得的痒螨mtDNA中筛选出分子标记基因，采用PCR技术扩增我国西南、华中、华北、华东和西北5大地区8个省14个采样点共128个绵羊痒螨（兔亚种）虫株的6个分子标记基因全序列，并进行种群遗传多样性分析。研究结果表明：（1）兔痒螨mtDNA全长14,247 bp，包含13个蛋白编码基因、22个tRNA基因及2个rRNA基因；其基因排列与已报道的美洲尘螨和椭圆食粉螨一致。BI树、ML树和MP树显示：蜱螨亚纲（Acari）分为寄螨总目Parasitiformes和真螨总目Acariformes，支持寄螨总目Parasitiformes、真螨总目Acariformes、真蜱目Ixodida、中气门目Mesostigmata以及无气门目Astigmata均分别为单系群。（2）经测序获得68条Cytb（1100 bp）、119条COI（1548 bp）、126条COII（769 bp）、89条12S rRNA（657 bp）、83条16S rRNA（1025 bp）和126条ITS（800 bp～804 bp）基因序列，这些序列分别有46个、104个、62个、50个、52个和92个单倍型，单倍型多样性（Hd）和核苷酸多样性（π）结果表明我国绵羊痒螨（兔亚种）具有丰富的遗传多样性，且遗传距离与地理距离的远近无关，种群的遗传变异主要发生在种群内部（AMOVA分析）；基于Fst值分析可见我国绵羊痒螨（兔亚种）各地理种群间存在一定的遗传分化但分化不明显，种群间基因交流频繁；中性检验呈现多峰的错配分布曲线现象；单倍型网络图和进化树表明我国绵羊痒螨（兔亚种）的聚类与兔种类、温度带和地理来源无关。由此可见，我国5个地区的绵羊痒螨（兔亚种）虫株呈现较高的遗传多样性，具有一定的遗传分化，但未形成以兔种类、温度带和地理分布为格局的遗传结构，结果将为痒螨病的流行病学调查、分子诊断等研究提供基础资料和指导作用。