Data from: Niche differentiation and colonization of a novel environment by an asexual parasitic wasp.

How do asexual taxa become adapted to a diversity of environments, and how do they persist despite changing environmental conditions? These questions are linked by their mutual focus on the relationship between genetic variation, which is often limited in asexuals, and the ability to respond to environmental variation. Asexual taxa originating from a single ancestor present a unique opportunity to assess rates of phenotypic and genetic change when access to new genetic variation is limited to mutation. Diachasma muliebre is an asexual Hymenopteran wasp that is geographically and genetically isolated from all sexual relatives. D. muliebre attack larvae of the western cherry fruit fly (Rhagoletis indifferens), which in turn feed inside bitter cherry fruit (Prunus emarginata) in August and September. R. indifferens has recently colonized a new host plant with an earlier fruiting phenology (June/July), domesticated sweet cherries (P. avium), and D. muliebre has followed its host into this temporally earlier niche. We tested three hypotheses: 1) that all D. muliebre lineages originate from a single asexual ancestor; 2) that different D. muliebre lineages (as defined by unique mtDNA haplotypes) have differentiated on their ancestral host in an important life-history trait, eclosion timing; and 3) that early-eclosing lineages have preferentially colonized the new sweet cherry niche. We find that mitochondrial COI and microsatellite data provide strong support for a single ancestral origin for all lineages. Furthermore, COI sequencing revealed five mitochondrial haplotypes among D. muliebre, and individual wasps possessing one distinctive mitochondrial haplotype (haplotype II) eclosed as reproductive adults significantly earlier than wasps with all other haplotypes. In addition, this early-eclosing lineage of D. muliebre is one of two lineages that have colonized the P. avium habitat, consistent with the preferential colonization hypothesis. These data suggest that D. muliebre has evolved adaptive phenotypic variation despite limited genetic variation, and that this variation has subsequently allowed an expansion of some wasps into a novel habitat. The D. muliebre system may allow for in-depth study of adaptation and long-term persistence of asexual taxa.

无性繁殖类群（asexual taxa）如何适应多样的环境，又如何在不断变化的环境条件下存续？这些问题的核心均聚焦于遗传变异——无性繁殖类群的遗传变异通常较为有限——与应对环境变异的能力之间的关联。由单一祖先演化而来的无性繁殖类群，为在新遗传变异仅能通过突变获取的前提下评估表型与遗传变化速率提供了独特的研究契机。

Diachasma muliebre是一种无性繁殖的膜翅目（Hymenopteran）蜂类，在地理与遗传上与所有有性近缘类群相互隔离。该蜂类的寄主为西部樱桃实蝇（Rhagoletis indifferens）的幼虫，而该实蝇于每年8至9月取食苦樱桃（Prunus emarginata）的果实。近期，西部樱桃实蝇侵染了一种结果物候更早的新寄主——驯化甜樱桃（Prunus avium，结果期为6至7月），而D. muliebre也跟随其寄主成功定殖了这个时间更早的生态位（niche）。

本研究检验了三项假说：其一，所有D. muliebre谱系均起源于单一无性祖先；其二，以独特线粒体DNA单倍型（haplotype）界定的不同D. muliebre谱系，在其祖先寄主上的关键生活史性状——羽化时间——发生了分化；其三，早羽化谱系优先定殖了新的甜樱桃生境。

研究结果显示，线粒体COI基因（mitochondrial COI）与微卫星（microsatellite）数据为所有谱系均起源于单一祖先提供了强有力的支持。此外，COI测序在D. muliebre中共发现5种线粒体单倍型，携带其中一种特殊单倍型（单倍型II）的个体，其羽化成为生殖成虫的时间显著早于携带其他所有单倍型的个体。进一步分析表明，该早羽化谱系是定殖了P. avium生境的两个谱系之一，与优先定殖假说相符。

上述数据表明，尽管遗传变异有限，D. muliebre仍演化出了适应性表型变异，且这种变异使得部分蜂类得以拓展至全新的生境。D. muliebre研究体系可为无性繁殖类群的适应性演化与长期存续提供深入研究的平台。