Department of Biology, Section for Computational and RNA Biology, University of Copenhagen, Copenhagen N, Denmark.
Norwegian College of Fishery Science, UiT The Arctic University of Norway, Tromsø, Norway.
Mol Ecol. 2021 Jan;30(2):528-544. doi: 10.1111/mec.15738. Epub 2020 Dec 22.
Grant's gazelles have recently been proposed to be a species complex comprising three highly divergent mtDNA lineages (Nanger granti, N. notata and N. petersii). The three lineages have nonoverlapping distributions in East Africa, but without any obvious geographical divisions, making them an interesting model for studying the early-stage evolutionary dynamics of allopatric speciation in detail. Here, we use genomic data obtained by restriction site-associated (RAD) sequencing of 106 gazelle individuals to shed light on the evolutionary processes underlying Grant's gazelle divergence, to characterize their genetic structure and to assess the presence of gene flow between the main lineages in the species complex. We date the species divergence to 134,000 years ago, which is recent in evolutionary terms. We find population subdivision within N. granti, which coincides with the previously suggested two subspecies, N. g. granti and N. g. robertsii. Moreover, these two lineages seem to have hybridized in Masai Mara. Perhaps more surprisingly given their extreme genetic differentiation, N. granti and N. petersii also show signs of prolonged admixture in Mkomazi, which we identified as a hybrid population most likely founded by allopatric lineages coming into secondary contact. Despite the admixed composition of this population, elevated X chromosomal differentiation suggests that selection may be shaping the outcome of hybridization in this population. Our results therefore provide detailed insights into the processes of allopatric speciation and secondary contact in a recently radiated species complex.
格兰特瞪羚最近被提议为一个物种复合体，由三个高度分化的线粒体 DNA 谱系（Nanger granti、N. notata 和 N. petersii）组成。这三个谱系在东非的分布没有重叠，但没有明显的地理划分，这使它们成为研究异域物种形成早期进化动态的有趣模型。在这里，我们使用通过 106 只瞪羚个体的限制性位点相关（RAD）测序获得的基因组数据，揭示了格兰特瞪羚分化的进化过程，描述了它们的遗传结构，并评估了物种复合体中主要谱系之间是否存在基因流。我们将物种分化的时间追溯到 134000 年前，这在进化上是最近的。我们发现 N. granti 内部存在种群分裂，这与先前提出的两个亚种 N. g. granti 和 N. g. robertsii 相吻合。此外，这两个谱系似乎在马赛马拉杂交。也许更令人惊讶的是，尽管它们的遗传分化极其明显，N. granti 和 N. petersii 也显示出在 Mkomazi 长期混合的迹象，我们将其鉴定为一个混合种群，最有可能是由于异域谱系的二次接触而形成的。尽管这个种群的组成是混合的，但升高的 X 染色体分化表明，选择可能正在塑造这个种群杂交的结果。因此，我们的研究结果为近期辐射物种复合体的异域物种形成和二次接触过程提供了详细的见解。
