Data from: Aphid specialization on different summer hosts is associated with strong genetic differentiation and unequal symbiont communities despite a common mating habitat

Specialization on different host plants can promote evolutionary diversification of herbivorous insects. Work on pea aphids (Acyrthosiphon pisum) has contributed significantly to the understanding of this process, demonstrating that populations associated with different host plants exhibit performance trade-offs across hosts, show adaptive host choice and genetic differentiation, and possess different communities of bacterial endosymbionts. Populations specialized on different secondary host plants during the parthenogenetic summer generations are also described for the black bean aphid (Aphis fabae complex) and are usually treated as different (morphologically cryptic) subspecies. In contrast to pea aphids, however, host choice and mate choice are decoupled in black bean aphids, because populations from different summer hosts return to the same primary host plant to mate and lay overwintering eggs. This could counteract evolutionary divergence, and it is currently unknown to what extent black bean aphids using different summer hosts are indeed differentiated. We addressed this question by microsatellite genotyping and endosymbiont screening of black bean aphids collected in summer from the goosefoot Chenopodium album (subspecies A. f. fabae) and from thistles of the genus Cirsium (subspecies A. f. cirsiiacanthoides) across numerous sites in Switzerland and France. Our results show clearly that aphids from Cirsium and Chenopodium show strong and geographically consistent genetic differentiation, and that they differ in their frequencies of infection with particular endosymbionts. The dependence on a joint winter host has thus not prevented the evolutionary divergence into summer host-adapted populations that appear to have evolved mechanisms of reproductive isolation within a common mating habitat.

寄主植物专化可推动植食性昆虫的演化分化。针对豌豆蚜（Acyrthosiphon pisum）的相关研究极大促进了学界对这一过程的认知，研究表明，与不同寄主植物建立关联的豌豆蚜种群，在不同寄主上呈现出适合度权衡现象，具备适应性寄主选择能力与遗传分化特征，且体内细菌内共生菌（endosymbiont）的群落组成存在显著差异。针对黑豆蚜复合群（Aphis fabae complex）的研究同样报道了其在孤雌生殖夏季世代中，对不同次生寄主植物形成特化的种群，这类种群通常被视为不同的（形态隐存）亚种。

然而与豌豆蚜不同，黑豆蚜的寄主选择与配偶选择存在解耦现象：来自不同夏季寄主的种群会回归同一原生寄主植物进行交配并产下越冬卵。这种特性可能会抵消演化分化进程，目前学界尚未明确，利用不同夏季寄主的黑豆蚜种群实际分化程度究竟如何。

本研究通过微卫星基因分型（microsatellite genotyping）与内共生菌筛查，对采自瑞士与法国多地夏季的黑豆蚜样本展开分析，样本分别采集自藜（Chenopodium album，对应亚种A. f. fabae）以及蓟属（Cirsium）蓟类植物（对应亚种A. f. cirsiiacanthoides），以此解答上述科学问题。研究结果清晰显示，采集自蓟属植物与藜的黑豆蚜种群存在显著且地理一致性的遗传分化，且二者的特定内共生菌感染频率存在差异。

由此可见，对共同冬季寄主的依赖并未阻碍演化分化进程：适应不同夏季寄主的种群已形成适应性分化，且似乎在共同的交配栖息地中演化出了生殖隔离机制。