Mouton L, Henri H, Bouletreau M, Vavre F
Laboratoire de Biométrie et Biologie Evolutive, Université Claude Bernard, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France.
Mol Ecol. 2003 Dec;12(12):3459-65. doi: 10.1046/j.1365-294x.2003.02015.x.
Vertically transmitted symbionts suffer a severe reduction in numbers when they pass through host generations, resulting in genetic homogeneity or even clonality of their populations. Wolbachia endosymbionts that induce cytoplasmic incompatibility in their hosts depart from this rule, because cytoplasmic incompatibility actively maintains multiple infection within hosts. Hosts and symbionts are thus probably under peculiar selective pressures that must shape the way intracellular bacterial populations are regulated. We studied the density and location of Wolbachia within adult Leptopilina heterotoma, a haplodiploid wasp that is parasitic on Drosophila and that is naturally infected with three Wolbachia strains, but for which we also obtained one simply infected and two doubly infected lines. Comparison of these four lines by quantitative polymerase chain reaction using a real-time detection system showed that total Wolbachia density varies according to the infection status of individuals, while the specific density of each Wolbachia strain remains constant regardless of the presence of other strains. This suggests that Wolbachia strains do not compete with one another within the same host individual, and that a strain-specific regulatory mechanism is operating. We discuss the regulatory mechanisms that are involved, and how this process might have evolved as a response to selective pressures acting on both partners.
垂直传播的共生体在宿主世代交替过程中数量会大幅减少，导致其种群出现基因同质化甚至克隆性。在宿主中引发细胞质不亲和的沃尔巴克氏体共生菌却背离了这一规律，因为细胞质不亲和会在宿主体内积极维持多重感染。因此，宿主和共生体可能处于特殊的选择压力之下，这必然会影响细胞内细菌种群的调控方式。我们研究了成年异角细蜂体内沃尔巴克氏体的密度和分布位置，异角细蜂是一种寄生在果蝇上的单双倍体黄蜂，自然感染了三种沃尔巴克氏体菌株，不过我们也获得了一个单感染品系和两个双感染品系。通过使用实时检测系统的定量聚合酶链反应对这四个品系进行比较，结果表明，总的沃尔巴克氏体密度因个体的感染状态而异，而每种沃尔巴克氏体菌株的特定密度无论其他菌株是否存在都保持恒定。这表明沃尔巴克氏体菌株在同一宿主个体内不会相互竞争，且存在一种菌株特异性调控机制在发挥作用。我们讨论了其中涉及的调控机制，以及这一过程可能是如何作为对作用于双方的选择压力的一种响应而进化的。
