Jiggins Francis M, Tinsley Matthew C
Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom.
Genetics. 2005 Nov;171(3):1115-24. doi: 10.1534/genetics.105.046342. Epub 2005 Aug 3.
Sex-ratio-distorting microbes are common parasites of arthropods. Although the reasons they have invaded and spread though populations are well understood, their subsequent dynamics within those populations are virtually unknown. We have found that different strains of a male-killing Rickettsia bacterium infecting the beetle Adalia bipunctata are associated with distinct mitochondrial haplotypes, which is expected as both the mitochondria and the bacteria are maternally transmitted. These mitochondrial haplotypes shared a common ancestor >2 million years ago, and their overall diversity is significantly greater than expected under neutrality from comparisons with a nuclear gene. Furthermore, a variety of statistical tests show strong deviations from neutrality in mitochondrial but not in nuclear genes. We therefore conclude that natural selection is probably maintaining a polymorphism of different Rickettsia strains in this species. Despite the age of the different mitochondrial haplotypes, there is very little genetic diversity within them. Furthermore, there is considerable variation in mitochondrial haplotype and bacterial strain frequency between populations, despite it being thought that this species has fairly low levels of population structure. We conclude that the fitness of these male killers may be negatively frequency dependent or different strains may be favored in different populations. These hypotheses await experimental confirmation.
导致性别比例失调的微生物是节肢动物常见的寄生虫。尽管它们侵入并在种群中传播的原因已为人熟知，但它们在这些种群中的后续动态却几乎无人知晓。我们发现，感染二斑叶螨的一种杀雄立克次氏体细菌的不同菌株与不同的线粒体单倍型相关联，这在意料之中，因为线粒体和细菌都是通过母系遗传的。这些线粒体单倍型在200多万年前有一个共同的祖先，与核基因相比，它们的总体多样性显著高于中性条件下的预期。此外，各种统计测试表明线粒体基因存在强烈的偏离中性现象，而核基因则没有。因此，我们得出结论，自然选择可能在维持该物种中不同立克次氏体菌株的多态性。尽管不同线粒体单倍型存在时间已久，但它们内部的遗传多样性却非常低。此外，尽管人们认为该物种的种群结构水平相当低，但不同种群之间线粒体单倍型和细菌菌株频率存在相当大的差异。我们得出结论，这些杀雄菌的适应性可能呈负频率依赖性，或者不同菌株在不同种群中受到青睐。这些假设有待实验证实。
