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.无性分类群如何适应多样的环境，又如何在不断变化的环境条件下得以存续？这类问题的核心均聚焦于遗传变异——通常在无性类群中较为有限——与响应环境变异的能力之间的关联。由单一祖先演化而来的无性分类群，为在新遗传变异仅能通过突变产生的限制条件下，评估表型与遗传变化的速率提供了独特的研究契机。雌性镰尾茧蜂（Diachasma muliebre）是一种无性膜翅目黄蜂，在地理与遗传层面均与所有有性近缘类群相互隔离。该蜂的寄主为西部樱桃实蝇（Rhagoletis indifferens）的幼虫，而西部樱桃实蝇于每年8至9月取食苦樱桃（Prunus emarginata）的果肉。近期，西部樱桃实蝇已成功定殖一种结果物候更早（6至7月）的新寄主——驯化甜樱桃（P. avium），而雌性镰尾茧蜂也随之跟随寄主进入这一时间窗口更靠前的生态位。本研究验证了三项假说：1）所有雌性镰尾茧蜂支系均源自单一无性祖先；2）以独特线粒体DNA（mtDNA）单倍型界定的不同支系，在其原始寄主上的关键生活史性状——羽化时间——已产生分化；3）羽化较早的支系会优先定殖新的甜樱桃生态位。研究结果显示，线粒体细胞色素C氧化酶亚基I（COI）与微卫星（microsatellite）标记的数据，为所有支系源自单一祖先的假说提供了强有力的支持。此外，COI测序结果显示雌性镰尾茧蜂中共存在5种线粒体单倍型，其中携带特定线粒体单倍型（单倍型II）的个体，其羽化成为可繁殖成虫的时间显著早于携带其余单倍型的个体。此外，这一羽化较早的支系是仅有的两个成功定殖甜樱桃（P. avium）生境的支系之一，与优先定殖假说的预测相符。上述数据表明，尽管遗传变异有限，雌性镰尾茧蜂仍演化出了适应性表型变异，而这类变异随后使得部分个体得以拓展至全新的生境中。雌性镰尾茧蜂这一研究体系，可为无性分类群的适应性演化与长期存续提供深入研究的契机。