Haygood Ralph, Turelli Michael
Department of Evolution and Ecology and Center for Population Biology, University of California, Davis, California 95616, USA.
Evolution. 2009 Feb;63(2):432-47. doi: 10.1111/j.1558-5646.2008.00550.x. Epub 2008 Dec 12.
Many insects, other arthropods, and nematodes harbor maternally inherited bacteria inducing "cytoplasmic incompatibility" (CI), reduced egg hatch when infected males mate with uninfected females. Although CI drives the spread of these microbes, selection on alternative, mutually compatible strains in panmictic host populations does not act directly on CI intensity but favors higher "effective fecundity," the number of infected progeny an infected female produces. We analyze the consequences of host population subdivision using deterministic and stochastic models. In subdivided populations, effective fecundity remains the primary target of selection. For strains of equal effective fecundity, if population density is regulated locally (i.e., "soft selection"), variation among patches in infection frequencies may induce change in the relative frequencies of the strains. However, whether this change favors stronger incompatibility depends on initial frequencies. Demographic fluctuations maintain frequency variation that tends to favor stronger incompatibility. However, this effect is weak; even with small patches, minute increases in effective fecundity can offset substantial decreases in CI intensity. These results are insensitive to many details of host life cycle and migration and to systematic outbreeding or inbreeding within patches. Selection acting through transfer between host species may be required to explain the prevalence of CI.
许多昆虫、其他节肢动物和线虫体内都携带着母系遗传的细菌，这些细菌会引发“细胞质不相容性”（CI），即当受感染的雄性与未受感染的雌性交配时，会导致卵孵化率降低。尽管细胞质不相容性推动了这些微生物的传播，但在随机交配的宿主种群中，对其他相互兼容菌株的选择并非直接作用于细胞质不相容性的强度，而是有利于更高的“有效繁殖力”，即受感染雌性所产生的受感染后代的数量。我们使用确定性模型和随机模型分析了宿主种群细分的后果。在细分的种群中，有效繁殖力仍然是选择的主要目标。对于有效繁殖力相同的菌株，如果种群密度在局部受到调节（即“软选择”），感染频率在斑块间的差异可能会导致菌株相对频率的变化。然而，这种变化是否有利于更强的不相容性取决于初始频率。种群动态波动维持着频率变化，这往往有利于更强的不相容性。然而，这种影响很微弱；即使斑块很小，有效繁殖力的微小增加也能抵消细胞质不相容性强度的大幅下降。这些结果对宿主生命周期和迁移的许多细节以及斑块内的系统杂交或近亲繁殖不敏感。可能需要通过宿主物种间的转移来解释细胞质不相容性的普遍存在。
