Data from: Differential introgression causes genealogical discordance in host races of Acrocercops transecta (Insecta: Lepidoptera)

Recently diverged populations often exhibit incomplete reproductive isolation, with a low level of gene flow continuing between populations. Previous studies have shown that, even under a low level of gene flow, genetic divergence between populations can proceed at the loci governing local adaptation and reproductive isolation but not at other neutral loci. A leaf-mining moth, Acrocercops transecta, consists of Juglans- and Lyonia-associated host races. The two host races differ in host preferences of ovipositing females and in larval adaptation to host plants but mate readily in the laboratory, producing fertile hybrids. The Juglans and Lyonia races are often sympatric in the wild, implying that gene introgression could occur in nature between the two host races. We tested this hypothesis by combining phylogenetic analyses with coalescent simulations, focusing on mitochondrial genes (COI and ND5) and the nuclear Tpi, Per and Ldh genes located on the Z-chromosome. The mitochondrial genes clearly distinguished the Lyonia race from the Juglnas race, whereas the Tpi, Per and Ldh genealogies did not reflect the two host races. Coalescent simulations indicated gene flow at the three Z-linked genes in both directions, whereas there was no introgression in the mitochondrial genes. The lack of introgression in mitochondrial genes suggests that female host preference is the primary force leading to the bifurcation of maternally inherited loci. Thus, the results show that a low level of gene flow coupled with the inflexible female host preference differentiates histories of divergence between maternally and biparentally inherited genes in this host race system.

新近分化的种群往往表现出不完全的生殖隔离，种群间仍维持着低水平的基因流。既往研究表明，即便基因流水平较低，种群间的遗传分化仍可在调控局部适应与生殖隔离的基因位点上发生，而在其他中性位点则不会。潜叶蛾物种斜纹细蛾（Acrocercops transecta）可分为两类寄主宗（host race），分别关联胡桃属（Juglans）与珍珠花属（Lyonia）植物。这两类寄主宗在产卵雌虫的寄主偏好以及幼虫对寄主植物的适应性上存在显著差异，但在实验室条件下可顺利交配并产生可育后代。胡桃属寄主宗与珍珠花属寄主宗在野外常呈同域分布，这暗示二者在自然环境中可能发生基因渐渗。我们通过结合系统发育分析与溯祖模拟（coalescent simulations）检验了这一假说，研究聚焦于线粒体基因（COI与ND5）以及位于Z染色体（Z-chromosome）上的核基因Tpi、Per与Ldh。结果显示，线粒体基因可清晰区分珍珠花属寄主宗与胡桃属寄主宗，而Tpi、Per与Ldh的基因谱系则未体现这两类寄主宗的分化。溯祖模拟结果表明，这三个Z连锁基因存在双向的基因流，而线粒体基因未发生基因渐渗。线粒体基因缺乏渐渗的现象表明，雌虫的寄主偏好是驱动母系遗传位点发生分化的核心作用力。综上，本研究结果证实，在该寄主宗系统中，低水平的基因流与固定不变的雌虫寄主偏好共同造就了母系遗传基因与双亲遗传基因之间分化历史的差异。