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.无性类群（asexual taxa）如何适应多样的环境，又如何在环境条件持续变化的情况下得以存续？这两个问题的核心均围绕遗传变异与环境响应能力之间的关联展开——无性类群的遗传变异通常较为有限，其环境适应能力亦受此制约。若无性类群的新遗传变异仅能通过突变产生，那么由单一祖先演化而来的无性类群，便为研究表型与遗传变化速率提供了绝佳的研究模型。孤雌绒茧蜂（Diachasma muliebre）是一种膜翅目无性繁殖蜂类，与所有有性近缘类群在地理与遗传上均相互隔离。该蜂会寄生西部樱桃实蝇（Rhagoletis indifferens）的幼虫，而西部樱桃实蝇的幼虫于每年8至9月取食苦樱桃（Prunus emarginata）的果肉。近期，西部樱桃实蝇已拓展至一种结果物候更早（6至7月）的新寄主——驯化甜樱桃（P. avium），而孤雌绒茧蜂也随之跟随寄主进入这一时间窗口更早的生态位。本研究验证了三项假说：1）所有孤雌绒茧蜂谱系均起源于单一无性祖先；2）以独特线粒体DNA（mtDNA）单倍型界定的不同孤雌绒茧蜂谱系，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）羽化时间较早的谱系会优先占据新的甜樱桃生态位。研究结果显示，线粒体细胞色素氧化酶亚基I（COI）与微卫星数据均强烈支持所有谱系均起源于单一祖先的假说。此外，COI测序结果在孤雌绒茧蜂中发现了5种线粒体单倍型，其中携带特殊单倍型II的个体，其羽化至生殖成虫的时间显著早于携带其他单倍型的个体。除此之外，这一羽化较早的孤雌绒茧蜂谱系，是仅有的两个成功占据甜樱桃（P. avium）生境的谱系之一，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，孤雌绒茧蜂仍演化出了适应性表型变异，而这种变异使得部分蜂类得以拓展至全新的生境中。孤雌绒茧蜂这一研究体系，可为无性类群的适应性演化与长期存续研究提供深入探索的契机。