Data from: Population genomics and geographical parthenogenesis in Japanese harvestmen (Opiliones, Sclerosomatidae, Leiobunum)

Naturally-occurring population variation in reproductive mode presents an opportunity for researchers to test hypotheses regarding the evolution of sex. Such populations frequently assume a geographical pattern, in which parthenogenesis-dominated populations are widely dispersed, with narrowly distributed sexual populations. We evaluate the geographic distribution of genomic signatures associated with parthenogenesis using nuclear and mitochondrial DNA sequence data from two Japanese harvestman sister taxa, Leiobunum manubriatum and L. globosum. Asexual reproduction is putatively facultative in these species, and female-biased localities are common in habitat margins. Past karyotypic and current cytometric work indicates L. globosum is entirely tetraploid, while L. manubriatum may be either diploid or tetraploid. We estimated species phylogeny, genetic differentiation, diversity, and mitonuclear discordance in females collected across the species range in order to identify range expansion towards marginal habitat, potential for hybrid origin, and persistence of asexual lineages. Our results point to northward expansion of a tetraploid ancestor of L. manubriatum and L. globosum, coupled with support for greater male gene flow in southern L. manubriatum localities. Specimens from localities in the Tohoku and Hokkaido regions were indistinct, particularly those of L. globosum, potentially due to little mitochondrial differentiation or haplotypic variation. Although L. manubriatum overlaps with L. globosum across its entire range, L. globosum was reconstructed as monophyletic with strong support using mtDNA, and marginal support with nuclear loci. Ultimately, we find evidence for continued sexual reproduction in both species, and describe opportunities to clarify the rate and mechanism of parthenogenesis.

自然存在的繁殖模式种群变异，为研究者检验有关有性生殖演化的假说提供了重要契机。此类种群往往呈现出特定的地理分布格局：以孤雌生殖（parthenogenesis）占主导的种群分布广泛，而有性生殖种群的分布范围则相对狭窄。本研究利用两种日本盲蛛姐妹类群——柄腹盲蛛（Leiobunum manubriatum）和球腹盲蛛（L. globosum）的核DNA与线粒体DNA序列数据，评估了与孤雌生殖相关的基因组特征的地理分布情况。这两个物种的无性生殖被认为是兼性的，且雌性占优的局部种群常见于生境边缘地带。既往的核型研究与当前的细胞计量学结果显示，球腹盲蛛完全为四倍体（tetraploid），而柄腹盲蛛则可能为二倍体（diploid）或四倍体。为了明确该类群向边缘生境的扩张范围、杂交起源的可能性以及无性谱系的存续情况，我们对横跨物种分布范围的雌性个体进行了物种系统发育、遗传分化、遗传多样性以及核质不协调（mitonuclear discordance）的评估。研究结果表明，柄腹盲蛛与球腹盲蛛的四倍体祖先曾向北扩张，同时支持在南部柄腹盲蛛的局部种群中存在更强的雄性基因流（gene flow）。来自日本东北地方（Tohoku）与北海道（Hokkaido）地区的种群样本，尤其是球腹盲蛛的样本，遗传特征并无明显差异，这可能是由于其线粒体分化程度极低或单倍型（haplotype）变异匮乏。尽管柄腹盲蛛的整个分布范围与球腹盲蛛完全重叠，但基于线粒体DNA的系统发育分析将球腹盲蛛重建为单系群（monophyletic），且支持度极高；而基于核基因座的分析则仅获得了微弱的支持。最终，我们在两个物种中均发现了持续进行有性生殖的证据，并阐明了进一步明确孤雌生殖速率与机制的研究方向。