Data from: Levels of clonal mixing in the black bean aphid Aphis fabae, a facultative ant mutualist

Aphids are a worldwide pest and an important model in ecology and evolution. Little is known, however, of the genetic structure of their colonies at a microgeographic level. For example, it remains largely unknown whether most species form monoclonal or polyclonal colonies. Here, we present the first detailed study on levels of clonal mixing in a nonsocial facultative ant mutualist, the black bean aphid Aphis fabae. In contrast to the earlier suggestion that colonies of this species are generally monoclonal, we found that across two subspecies of the black bean aphid, A. fabae cirsiiacanthoidis and A. fabae fabae, 32% and 77% of the aphid colonies were in fact polyclonal, consisting of a mix of up to 4 different clones, which resulted in an overall average relatedness within colonies of 0.90 and 0.79 in the two subspecies. Data further show that the average relatedness in A. f. cirsiiacanthoidis remained relatively constant throughout the season, which means that clonal erosion due to clonal selection more or less balanced with the influx of new clones from elsewhere. Nevertheless, relatedness tended to decrease over the lifetime of a given colony, implying that clonal mixing primarily resulted from the joining of preexisting colonies as opposed to via simultaneous host colonisation by several foundresses. Widespread clonal mixing is argued to affect the ecology and evolution of the aphids in various important ways, for example with respect to the costs and benefits of group living, the evolution of dispersal and the interaction with predators as well as with the ant mutualists.

蚜虫是全球性害虫，同时也是生态学与进化研究领域的重要模式类群。然而，学界对其种群在微地理尺度下的遗传结构仍知之甚少。例如，多数蚜虫物种是否会形成单克隆（monoclonal）或多克隆（polyclonal）种群，目前仍未明确。
本研究首次针对一种非社会性兼性蚁共生生物（nonsocial facultative ant mutualist）——黑菜蚜（Aphis fabae）的克隆混合（clonal mixing）水平开展了详细研究。与此前认为该物种种群普遍为单克隆的观点相悖，我们在黑菜蚜的两个亚种——A. fabae cirsiiacanthoidis与A. fabae fabae——的调查中发现，分别有32%与77%的蚜虫种群实际为多克隆种群，最多可包含4种不同的克隆；这使得两个亚种的种群内平均亲缘系数（relatedness）分别为0.90与0.79。
进一步数据分析显示，A. f. cirsiiacanthoidis的种群平均亲缘系数在整个观测季中相对稳定，这表明由克隆选择（clonal selection）引发的克隆衰退（clonal erosion），与来自其他区域的新克隆迁入大致保持平衡。尽管如此，单个种群的存续周期内，亲缘系数往往会逐渐降低，这表明克隆混合主要源于已形成种群的融合，而非由多个建群雌蚜（foundresses）同时侵染寄主所导致。
学界普遍认为，广泛存在的克隆混合会从多个重要维度影响蚜虫的生态学特征与进化历程，例如群居生活的成本与收益、扩散（dispersal）性状的进化，以及蚜虫与天敌（predators）、蚁共生生物（ant mutualists）之间的互作关系。