Data from: Haldane's rule is linked to extraordinary sex ratios and sperm length in stalk-eyed flies.

We use three allopatric populations of the stalk-eyed fly Teleopsis dalmanni from Southeast Asia to test two predictions made by the sex chromosome drive hypothesis for Haldane's rule. The first is that modifiers that suppress or enhance drive should evolve rapidly and independently in isolated populations. The second is that drive loci or modifiers should also cause sterility in hybrid males. We tested these predictions by assaying the fertility of 2,066 males derived from backcross experiments involving two pairs of populations and found that the proportion of mated males that fail to produce any offspring ranged from 38-60% among crosses with some males producing strongly female-biased or male-biased sex ratios. After genotyping each male at 25-28 genetic markers we found quantitative trait loci (QTL) that jointly influence male sterility, sperm length and biased progeny sex ratios in each pair of populations, but almost no shared QTL between population crosses. We also discovered that the extant XSR chromosome has no effect on sex ratio or sterility in these backcross males. Whether shared QTL are caused by linkage or pleiotropy requires additional study. Nevertheless, these results indicate the presence of a "cryptic" drive system that is currently masked by suppressing elements that are associated with sterility and sperm length within but not between populations and, therefore, must have evolved since the populations became isolated, i.e. in less than 100,000 years. We discuss how genes that influence sperm length may contribute to hybrid sterility.

本研究选取东南亚地区的泰氏柄眼蝇（Teleopsis dalmanni，stalk-eyed fly）的3个异域种群，针对霍尔丹法则（Haldane's rule）的性染色体驱动假说（sex chromosome drive hypothesis）所提出的两项预测展开验证。第一项预测为：能够抑制或增强驱动效应的修饰因子，应在隔离种群中快速且独立地演化。第二项预测为：驱动位点或修饰因子同样会导致杂交雄性不育。我们通过涉及2组种群对的回交实验（backcross experiments），对总计2066只雄性个体的育性进行了检测，结果显示：在不同杂交组合中，成功交配但未产生任何后代的雄性个体占比介于38%至60%之间，部分雄性的后代性别比例呈现显著的雌性偏倚或雄性偏倚。我们对每只雄性个体的25至28个遗传标记完成基因分型后，在每组种群对中均鉴定到可同时影响雄性不育性、精子长度以及后代偏倚性别比例的数量性状位点（quantitative trait loci，QTL）；但不同种群对的杂交组合间几乎不存在共享的QTL。我们还发现，现存的XSR染色体（XSR chromosome）对这些回交雄性的性别比例与育性均无显著影响。共享QTL究竟源于基因连锁还是多效性，仍需后续研究进一步验证。尽管如此，本研究结果表明存在一套“隐秘”的驱动系统：该系统目前被种群内部（而非种群间）与不育性及精子长度相关的抑制因子所遮蔽，因此其演化必然发生在种群彼此隔离之后，即距今不足10万年的时间尺度内。我们还探讨了影响精子长度的基因可能通过何种途径参与杂交不育的形成。