Kern Peter, Cook James M, Kageyama Daisuke, Riegler Markus
Hawkesbury Institute for the Environment, University of Western Sydney, Locked Bag 1797, Penrith, New South Wales 2751, Australia.
National Institute of Agrobiological Sciences (NIAS), 1-2 Owashi, Tsukuba, Ibaraki 305-8634, Japan
Biol Lett. 2015 May;11(5):20150095. doi: 10.1098/rsbl.2015.0095.
Arthropod sex ratios can be manipulated by a diverse range of selfish genetic elements, including maternally inherited Wolbachia bacteria. Feminization by Wolbachia is rare but has been described for Eurema mandarina butterflies. In this species, some phenotypic and functional females, thought to be ZZ genetic males, are infected with a feminizing Wolbachia strain, wFem. Meanwhile, heterogametic WZ females are not infected with wFem. Here, we establish a quantitative PCR assay allowing reliable sexing in three Eurema species. Against expectation, all E. mandarina females, including wFem females, had only one Z chromosome that was paternally inherited. Observation of somatic interphase nuclei confirmed that W chromatin was absent in wFem females, but present in females without wFem. We conclude that the sex bias in wFem lines is due to meiotic drive (MD) that excludes the maternal Z and thus prevents formation of ZZ males. Furthermore, wFem lines may have lost the W chromosome or harbour a dysfunctional version, yet rely on wFem for female development; removal of wFem results in all-male offspring. This is the first study that demonstrates an interaction between MD and Wolbachia feminization, and it highlights endosymbionts as potentially confounding factors in MD of sex chromosomes.
节肢动物的性别比例可被多种自私遗传元件操纵，包括母系遗传的沃尔巴克氏体细菌。沃尔巴克氏体导致的雌性化现象较为罕见，但在柑桔凤蝶中已有报道。在该物种中，一些表型和功能上为雌性的个体，被认为是ZZ基因型的雄性，感染了一种导致雌性化的沃尔巴克氏体菌株wFem。与此同时，异配性别WZ的雌性未感染wFem。在此，我们建立了一种定量PCR检测方法，可对三种凤蝶物种进行可靠的性别鉴定。与预期相反，所有柑桔凤蝶雌性，包括感染wFem的雌性，都只有一条来自父系遗传的Z染色体。对体细胞间期核的观察证实，感染wFem的雌性中不存在W染色质，而未感染wFem的雌性中存在W染色质。我们得出结论，wFem品系中的性别偏差是由于减数分裂驱动（MD）导致母本的Z染色体被排除，从而阻止了ZZ雄性的形成。此外，wFem品系可能已经丢失了W染色体或含有功能失调的W染色体版本，但依赖wFem进行雌性发育；去除wFem会导致产生全雄后代。这是第一项证明减数分裂驱动与沃尔巴克氏体雌性化之间相互作用的研究，它突出了内共生体作为性染色体减数分裂驱动中潜在混杂因素的作用。
