Data from: Elevated genetic diversity of mitochondrial genes in asexual populations of bark lice ("Psocoptera": Echmepteryx hageni)

Asexual reproduction is commonly thought to be associated with low genetic diversity in animals. Echmepteryx hageni (Insecta: “Psocoptera”) is one of several psocopteran species that are primarily parthenogenetic, but also exists in small, isolated sexual populations. We used mitochondrial DNA sequences to investigate the population history and genealogical relationships between the sexual and asexual forms of this species. The asexual population of E. hageni exhibits extremely high mitochondrial haplotype diversity (H = 0.98), whereas the sexual forms had significantly lower haplotypic diversity (H = 0.25, after correcting for sample size). This diversity in asexuals represents one the greatest genetic diversities reported for asexual animals in the literature. Nucleotide diversities were also higher in asexual compared to sexual populations (π = 0.0071 vs. 0.00027). Compared to other reported estimates of π in insects, asexual nucleotide diversity is high, but not remarkably elevated. Three hypotheses might explain the elevated genetic diversity of asexual populations: 1) larger effective population size, 2) greater mutation rate, or 3) possible recent origin of sexuals. In addition, phylogeographic analysis revealed little geographic structure among asexual E. hageni, although specimens from the upper Midwest form a single clade and are genetically differentiated. The mismatch distribution and neutrality tests indicate a historical population size increase, possibly associated with expansion from glacial refugia.

学界普遍认为，无性繁殖（asexual reproduction）与动物的低遗传多样性紧密相关。哈氏棒啮虫（Echmepteryx hageni，昆虫纲：‘啮虫目（Psocoptera）’）是少数以孤雌生殖（parthenogenesis）为主要繁殖策略的啮虫目物种，同时也存在小型隔离的有性繁殖种群。本研究借助线粒体DNA（mitochondrial DNA）序列，解析了该物种有性与无性繁殖种群的种群历史及谱系亲缘关系。哈氏棒啮虫的无性繁殖种群展现出极高的线粒体单倍型多样性（mitochondrial haplotype diversity，H=0.98），而有性繁殖种群的单倍型多样性则显著更低（校正样本量后H=0.25）。该无性种群的遗传多样性，是已发表文献中报道的无性繁殖动物最高遗传多样性之一。无性种群的核苷酸多样性（nucleotide diversity）同样高于有性种群（π=0.0071 与 0.00027）。相较于已报道的昆虫核苷酸多样性估算值，该无性种群的核苷酸多样性虽处于较高水平，但并未出现显著升高。现有三种假说可解释无性种群升高的遗传多样性：1）更大的有效种群规模（effective population size）；2）更高的突变率；3）有性种群的起源时间较晚。此外，谱系地理学（phylogeography）分析显示，哈氏棒啮虫的无性种群几乎不存在地理结构分化，但来自美国中西部北部的标本构成了一个单系群（clade），且在遗传层面存在显著分化。错配分布（mismatch distribution）与中性检验（neutrality test）结果表明，该物种曾经历过种群历史规模扩张，这一过程可能与冰期避难所（glacial refugia）的种群扩散相关。