Microb Ecol. 2014 Jan;67(1):195-204. doi: 10.1007/s00248-013-0314-0.
Facultative bacterial endosymbionts can play an important role in the evolutionary trajectory of their hosts. Aphids (Hemiptera: Aphididae) are infected with a wide variety of facultative endosymbionts that can confer ecologically relevant traits, which in turn may drive microevolutionary processes in a dynamic selective environment. However, relatively little is known about how symbiont diversity is structured in most aphid species. Here, we investigate facultative symbiont species richness and prevalence among world-wide populations of the cowpea aphid, Aphis craccivora Koch. We surveyed 44 populations of A. craccivora, and detected 11 strains of facultative symbiotic bacteria, representing six genera. There were two significant associations between facultative symbiont and aphid food plant: the symbiont Arsenophonus was found at high prevalence in A. craccivora populations collected from Robinia sp. (locust), whereas the symbiont Hamiltonella was almost exclusively found in A. craccivora populations from Medicago sativa (alfalfa). Aphids collected from these two food plants also had divergent mitochondrial haplotypes, potentially indicating the formation of specialized aphid lineages associated with food plant (host-associated differentiation). The role of facultative symbionts in this process remains to be determined. Overall, observed facultative symbiont prevalence in A. craccivora was lower than that of some other well-studied aphids (e.g., Aphis fabae and Acyrthosiphon pisum), possibly as a consequence of A. craccivora's almost purely parthenogenetic life history. Finally, most (70 %) of the surveyed populations were polymorphic for facultative symbiont infection, indicating that even when symbiont prevalence is relatively low, symbiont-associated phenotypic variation may allow population-level evolutionary responses to local selection.
兼性细菌内共生体在宿主的进化轨迹中可以发挥重要作用。蚜虫（半翅目：蚜虫科）感染了各种各样的兼性内共生体，这些共生体可以赋予具有生态相关性的特征，进而在动态选择环境中推动微进化过程。然而，对于大多数蚜虫物种中共生体多样性的结构，我们知之甚少。在这里，我们研究了在豇豆花叶病毒广泛分布的种群中兼性共生体的物种丰富度和流行程度。我们调查了 44 个豇豆花叶病毒种群，检测到 11 种兼性共生细菌，代表 6 个属。兼性共生体和蚜虫食物植物之间存在两个显著的关联：共生体 Arsenophonus 在从豆科植物（刺槐）收集的豇豆花叶病毒种群中发现率较高，而共生体 Hamiltonella 几乎只存在于从紫花苜蓿（紫花苜蓿）收集的豇豆花叶病毒种群中。从这两种食物植物中收集的蚜虫也具有不同的线粒体单倍型，这可能表明与食物植物相关的专门蚜虫谱系的形成（与宿主相关的分化）。在这个过程中，兼性共生体的作用仍有待确定。总的来说，在豇豆花叶病毒中观察到的兼性共生体的流行率低于其他一些研究充分的蚜虫（例如，蚕豆蚜和豌豆蚜），这可能是由于豇豆花叶病毒几乎完全是孤雌生殖的生活史所致。最后，调查的大多数（70%）种群在兼性共生体感染方面表现出多态性，这表明即使兼性共生体的流行率相对较低，共生体相关的表型变异也可能允许种群水平对局部选择做出进化反应。
