Department of Evolution and Phylogeny, Primate Research Institute, Kyoto University, Aichi, Japan.
School of Mathematical and Natural Sciences, New College of Interdisciplinary Arts and Sciences, Arizona State University West Campus, Glendale, AZ, USA.
J Evol Biol. 2020 Sep;33(9):1164-1179. doi: 10.1111/jeb.13681. Epub 2020 Jul 31.
Understanding the process and consequences of hybridization is one of the major challenges in evolutionary biology. A growing body of literature has reported evidence of ancient hybridization events or natural hybrid zones in primates, including humans; however, we still have relatively limited knowledge about the pattern and history of admixture because there have been little studies that simultaneously achieved genome-scale analysis and a geographically wide sampling of wild populations. Our study applied double-digest restriction site-associated DNA sequencing to samples from the six localities in and around the provisional hybrid zone of rhesus and long-tailed macaques and evaluated population structure, phylogenetic relationships, demographic history, and geographic clines of morphology and allele frequencies. A latitudinal gradient of genetic components was observed, highlighting the transition from rhesus (north) to long-tailed macaque distribution (south) as well as the presence of one northern population of long-tailed macaques exhibiting unique genetic structure. Interspecific gene flow was estimated to have recently occurred after an isolation period, and the migration rate from rhesus to long-tailed macaques was slightly greater than in the opposite direction. Although some rhesus macaque-biased alleles have widely introgressed into long-tailed macaque populations, the inflection points of allele frequencies have been observed as concentrated around the traditionally recognized interspecific boundary where morphology discontinuously changed; this pattern was more pronounced in the X chromosome than in autosomes. Thus, due to geographic separation before secondary contact, reproductive isolation could have evolved, contributing to the maintenance of an interspecific boundary and species-specific morphological characteristics.
了解杂交的过程和后果是进化生物学的主要挑战之一。越来越多的文献报道了灵长类动物（包括人类）中古代杂交事件或自然杂交区的证据；然而，由于几乎没有同时进行全基因组分析和对野生种群进行广泛地理采样的研究，我们对混合的模式和历史仍然知之甚少。我们的研究应用双酶切限制位点相关 DNA 测序对来自暂定杂交区及其周围的六个地点的恒河猴和长尾猕猴样本进行了分析，并评估了种群结构、系统发育关系、种群历史以及形态和等位基因频率的地理渐变。观察到遗传成分的纬度梯度，突出了从恒河猴（北部）到长尾猕猴分布（南部）的过渡，以及一个具有独特遗传结构的北部长尾猕猴种群的存在。种间基因流估计是在隔离期后最近发生的，从恒河猴到长尾猕猴的迁移率略高于相反方向。尽管一些恒河猴偏向的等位基因已广泛渗入长尾猕猴种群，但等位基因频率的拐点被观察到集中在传统上公认的种间边界附近，形态在此处发生不连续变化；这种模式在 X 染色体上比在常染色体上更为明显。因此，由于在二次接触之前的地理分离，生殖隔离可能已经进化，有助于维持种间边界和物种特异性的形态特征。
