Data from: A reassessment of explanations for discordant introgressions of mitochondrial and nuclear genomes

Hybridization is increasingly recognized as a significant evolutionary process, in particular because it can lead to introgression of genes from one species to another. A striking pattern of discordance in the amount of introgression between mitochondrial and nuclear markers exists such that substantial mitochondrial introgression is often found in combination with no or little nuclear introgression. Multiple mechanisms have been proposed to explain this discordance, including positive selection for introgressing mitochondrial variants, several types of sex-biases, drift, negative selection against introgression in the nuclear genome, and spatial expansion. Most of these hypotheses are verbal, and have not been quantitatively evaluated so far. We use individual-based, multi-locus, computer simulations of secondary contact under a wide range of demographic and genetic scenarios to evaluate the ability of the different mechanisms to produce discordant introgression. Sex-biases and spatial expansions fail to produce substantial mito-nuclear discordance. Drift and nuclear selection can produce strong discordance, but only under a limited range of conditions. In contrast, selection on the mitochondrial genome produces strong discordance, particularly when dispersal rates are low. However, commonly used statistical tests have little power to detect this selection. Altogether, these results dismiss several popular hypotheses, and provide support for adaptive mitochondrial introgression.

杂交（Hybridization）日益被学界视为一项重要的演化过程，尤其是其可介导基因从一个物种向另一物种的渐渗（introgression）。当前已观测到一类显著的模式：线粒体与核标记间的渐渗量存在明显不一致，即常可发现大量线粒体基因渐渗，却伴随无或极少量的核基因渐渗。目前学界已提出多种机制以解释这种不一致性，包括对渐渗线粒体变异的正选择、多种类型的性别偏向、遗传漂变、核基因组中针对渐渗的负选择，以及空间扩张。这些假说大多仅为定性描述，迄今尚未得到定量评估。本研究采用基于个体、多位点的计算机模拟方法，在广泛的种群统计与遗传场景下模拟二次接触（secondary contact）过程，以评估不同机制产生渐渗不一致性的能力。结果表明，性别偏向与空间扩张无法产生显著的线粒体-核基因渐渗不一致性；遗传漂变与核选择虽可产生较强的不一致性，但仅能在有限的条件范围内实现；与之相反，线粒体基因组上的选择可产生强烈的渐渗不一致性，尤其当扩散速率较低时。然而，常用的统计检验（statistical tests）几乎没有能力检测到这类选择。综上，本研究结果否定了数种主流假说，并为适应性线粒体基因渐渗（adaptive mitochondrial introgression）提供了支持。