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...杂交（Hybridization）日益被视为一种关键的演化过程，尤其是因其可介导基因从一个物种向另一物种的渐渗（introgression）。目前已发现一类显著的线粒体与核标记间渐渗量不一致模式：即通常可观测到大量线粒体渐渗，却伴随无或极微量的核渐渗。学界已提出多种机制以解释该不一致性，包括对渐渗线粒体变异体的正选择、多种类型的性别偏向、遗传漂变、核基因组中针对渐渗事件的负选择，以及空间扩张。上述假说大多为定性描述，迄今尚未得到定量评估。我们采用基于个体、多位点的计算机模拟方法，在广泛的种群统计与遗传情景下模拟二次接触（secondary contact）过程，以评估不同机制产生渐渗不一致性的能力。性别偏向与空间……