Keais G L, Hanson M A, Gowen B E, Perlman S J
Department of Biology, University of Victoria, Victoria, BC, Canada.
J Evol Biol. 2017 Jun;30(6):1185-1194. doi: 10.1111/jeb.13089. Epub 2017 May 13.
Selfish genes that bias their own transmission during meiosis can spread rapidly in populations, even if they contribute negatively to the fitness of their host. Driving X chromosomes provide a clear example of this type of selfish propagation. These chromosomes have important evolutionary and ecological consequences, and can be found in a broad range of taxa including plants, mammals and insects. Here, we report a new case of X chromosome drive (X drive) in a widespread woodland fly, Drosophila testacea. We show that males carrying the driving X (SR males) sire 80-100% female offspring and possess a diagnostic X chromosome haplotype that is perfectly associated with the sex ratio distortion phenotype. We find that the majority of sons produced by SR males are sterile and appear to lack a Y chromosome, suggesting that meiotic defects involving the Y chromosome may underlie X drive in this species. Abnormalities in sperm cysts of SR males reflect that some spermatids are failing to develop properly, confirming that drive is acting during gametogenesis. By screening wild-caught flies using progeny sex ratios and a diagnostic marker, we demonstrate that the driving X is present in wild populations at a frequency of ~ 10% and that suppressors of drive are segregating in the same population. The testacea species group appears to be a hot spot for X drive, and D. testacea is a promising model to compare driving X chromosomes in closely related species, some of which may even be younger than the chromosomes themselves.
在减数分裂过程中偏向自身传递的自私基因能够在种群中迅速传播，即便它们对宿主的适应性产生负面影响。驱动性X染色体便是这种自私传播类型的一个明显例子。这些染色体具有重要的进化和生态影响，并且在包括植物、哺乳动物和昆虫在内的广泛分类群中都能找到。在此，我们报告了在一种广泛分布的林地果蝇——坚果蝇（Drosophila testacea）中发现的一个新的X染色体驱动（X drive）案例。我们发现携带驱动性X染色体的雄性（SR雄性）产生80% - 100%的雌性后代，并且拥有一种与性别比例扭曲表型完美相关的诊断性X染色体单倍型。我们发现SR雄性产生的大多数儿子是不育的，并且似乎缺少Y染色体，这表明涉及Y染色体的减数分裂缺陷可能是该物种中X驱动的基础。SR雄性精子囊肿的异常反映出一些精子细胞发育不正常，证实了驱动作用发生在配子发生过程中。通过利用后代性别比例和一个诊断标记物对野生捕获的果蝇进行筛选，我们证明驱动性X染色体在野生种群中的频率约为10%，并且驱动抑制因子在同一群体中正在分离。坚果蝇物种组似乎是X驱动的一个热点，并且坚果蝇是比较近缘物种中驱动性X染色体的一个有前景的模型，其中一些物种甚至可能比这些染色体本身还要年轻。
