Phylogenetics of Aphids and Their Intracellular Associates and Implications for the Evolutionary History of the Endosymbiosis

许多动植物物种含有细菌，称为内共生体，它们栖息在宿主的特殊细胞中。这些关联广泛存在于以植物汁液为食的昆虫中，包括蚜虫及其进化的近亲。没有内共生体，昆虫就不能生长或繁殖，特殊的机制确保后代在出生时就被感染。亚利桑那大学的南希·莫兰博士与加州大学戴维斯分校的保罗·鲍曼博士合作，致力于重建蚜虫及相关昆虫内共生生物的进化史，以确定细菌和昆虫之间的多样性。他们正在分析来自细菌及其宿主的核糖体DNA的核苷酸序列数据，以通过测量分类群之间的突变差异来推断该物种的系统发育树。对这些系统发育树的对应关系或缺乏对应关系的分析将有助于确定细菌是否与宿主并行地多样化，或者不相关的细菌群体是否随着时间的推移频繁入侵新的昆虫宿主。这些数据还将允许估计缔合的年龄和分子变化的速度。这些发现应该能从总体上阐明内共生关系的本质，并将有助于理解这一重要昆虫群体的进化。

Many animal and plant species contain bacteria, called endosymbionts, that inhabit specialized cells of their hosts. These associations are widespread in insects that feed on plant sap, including aphids and their evolutionary relatives. The insects cannot grow or reproduce without their endosymbionts, and specialized mechanisms ensure that offspring are infected at birth. Dr. Nancy Moran of the University of Arizona, collaborating with Dr. Paul Baumann at the University of California-Davis, is working to reconstruct the evolutionary history of the endosymbioses of aphids and related insects, in order to determine how the bacteria and insects have diversified in association with one another. They are analyzing nucleotide sequence data from ribosomal DNA from both bacteria and their hosts in order to infer phylogenetic trees of the species, by measuring mutational differences among the taxa. Analysis of the correspondence, or lack thereof, of these phylogenetic trees will permit a determination of whether the bacteria have diversified in parallel with hosts or whether unrelated groups of bacteria have frequently invaded new insect hosts through time. The data will also allow an estimate of the ages of the associations and of rates of molecular change. The findings should illuminate the nature of endosymbiotic associations in general and will aid in understanding the evolution of this important group of insects.