Blackmon Heath, Hardy Nate B, Ross Laura
Department of Biology, University of Texas, Arlington, Box 19498, Arlington, Texas, 76019.
Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama, 36849.
Evolution. 2015 Nov;69(11):2971-8. doi: 10.1111/evo.12792. Epub 2015 Nov 2.
Haplodiploid reproduction, in which males are haploid and females are diploid, is widespread among animals, yet we understand little about the forces responsible for its evolution. The current theory is that haplodiploidy has evolved through genetic conflicts, as it provides a transmission advantage to mothers. Male viability is thought to be a major limiting factor; diploid individuals tend to harbor many recessive lethal mutations. This theory predicts that the evolution of haplodiploidy is more likely in male heterogametic lineages with few chromosomes, as genes on the X chromosome are often expressed in a haploid environment, and the fewer the chromosome number, the greater the proportion of the total genome that is X-linked. We test this prediction with comparative phylogenetic analyses of mites, among which haplodiploidy has evolved repeatedly. We recover a negative correlation between chromosome number and haplodiploidy, find evidence that low chromosome number evolved prior to haplodiploidy, and that it is unlikely that diplodiploidy has reevolved from haplodiploid lineages of mites. These results are consistent with the predicted importance of haploid male viability.
单双倍体生殖，即雄性为单倍体而雌性为双倍体，在动物中广泛存在，但我们对其进化的驱动因素了解甚少。当前的理论认为，单双倍体是通过基因冲突进化而来的，因为它为母亲提供了一种遗传优势。雄性的生存能力被认为是一个主要的限制因素；双倍体个体往往携带许多隐性致死突变。该理论预测，在染色体数量较少的雄性异配性别谱系中，单双倍体的进化更有可能发生，因为X染色体上的基因通常在单倍体环境中表达，而且染色体数量越少，X连锁的基因组在整个基因组中所占的比例就越大。我们通过对螨类进行比较系统发育分析来检验这一预测，在螨类中，单双倍体已经多次进化。我们发现染色体数量与单双倍体之间呈负相关，有证据表明低染色体数量在单双倍体之前就已进化，而且双倍体不太可能从螨类的单双倍体系谱中再次进化而来。这些结果与单倍体雄性生存能力的预测重要性相一致。
