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生物学研究中的重要模式系统。然而，学界对其种群在微地理尺度下的遗传结构却知之甚少。例如，绝大多数蚜虫物种是否形成单克隆或多克隆种群，目前仍未明确。本研究首次针对非社会性兼性蚁共生昆虫——黑菜蚜（Aphis fabae）的克隆混合水平展开了详尽研究。与此前认为该物种种群多为单克隆的观点相悖，我们在黑菜蚜的两个亚种——蓟刺菜蚜亚种（Aphis fabae cirsiiacanthoidis）与指名亚种（Aphis fabae fabae）——中发现，分别有32%与77%的蚜虫种群实为多克隆种群，其克隆组成最多包含4种不同克隆；这使得两个亚种的种群内平均亲缘系数分别为0.90与0.79。进一步的数据显示，蓟刺菜蚜亚种的种群平均亲缘系数在整个发生季中保持相对稳定，这表明由克隆选择引发的克隆侵蚀，与外界新克隆的迁入过程大致保持平衡。尽管如此，单个种群的存续周期内，亲缘系数往往呈下降趋势，这表明克隆混合主要源于已形成种群的融合，而非多个创始雌虫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与进化过程，例如群体生活的成本与收益、扩散能力的演化，以及蚜虫与天敌、蚁共生伙伴的互作关系。