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）正日益受到学界认可为一类重要的进化过程，尤其是因为其可介导不同物种间的基因渐渗（introgression）。学界已观测到一类显著的模式：线粒体标记与核标记（mitochondrial and nuclear markers）间的基因渐渗水平存在显著不一致，即常可观测到显著的线粒体基因渐渗，却伴随无或极微弱的核基因渐渗。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体的正向选择、多类性别偏向性因素、遗传漂变、针对核基因组渐渗的负向选择，以及空间扩张效应。上述多数假说均为定性描述，迄今尚未得到定量验证。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参数场景下模拟次生接触（secondary contact）过程，以评估不同机制产生基因渐渗不一致性的能力。结果显示，性别偏向性因素与空间扩张效应均无法产生显著的线粒体-核基因渐渗不一致性；遗传漂变与核基因组选择虽可产生显著的不一致性，但仅能在有限的参数条件下实现。与之相反，线粒体基因组上的选择可产生显著的渐渗不一致性，尤其在扩散速率较低的场景下。但当前常用的统计检验方法对这类选择的检测效力极低。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提供了支持证据。