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.

新近分化的种群通常呈现不完全的生殖隔离（reproductive isolation），种群间仍存在低水平的基因流（gene flow）。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性与生殖隔离的基因座上发生，而在其他中性基因座（neutral loci）上则不会。一种潜叶蛾（leaf-mining moth）*Acrocercops transecta* 包含两个寄主宗（host race）：胡桃属（Juglans）寄主宗与南烛属（Lyonia）寄主宗。这两个寄主宗在产卵雌虫（ovipositing females）的寄主偏好以及幼虫适应性（larval adaptation）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。胡桃属寄主宗与南烛属寄主宗在野外常呈同域分布（sympatric），这提示二者在自然环境中可能发生基因渐渗（gene introgression）。本研究通过结合系统发育分析（phylogenetic analyses）与溯祖模拟（coalescent simulations）对该假说进行验证，重点关注线粒体基因（mitochondrial genes，包括COI与ND5）以及位于Z染色体（Z-chromosome）上的核基因*Tpi*、*Per*与*Ldh*。线粒体基因可清晰区分南烛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个寄主宗的分化。溯祖模拟结果显示，这三个Z连锁基因存在双向的基因流，而线粒体基因则未发生基因渐渗。线粒体基因未发生基因渐渗这一现象提示，雌虫的寄主偏好是导致母系遗传基因座发生分化的主要驱动力。综上，本研究结果表明，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成了母系遗传基因与双亲遗传基因的分化历史差异。