Owens Gregory L, Todesco Marco, Bercovich Natalia, Légaré Jean-Sébastien, Mitchell Nora, Whitney Kenneth D, Rieseberg Loren H
Department of Biology, University of Victoria, Victoria, BC, Canada.
Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada.
Mol Ecol. 2021 Dec;30(23):6229-6245. doi: 10.1111/mec.16008. Epub 2021 Jun 19.
The origins of geographic races in wide-ranging species are poorly understood. In Texas, the texanus subspecies of Helianthus annuus has long been thought to have acquired its defining phenotypic traits via introgression from a local congener, H. debilis, but previous tests of this hypothesis were inconclusive. Here, we explore the origins of H. a. texanus using whole genome sequencing data from across the entire range of H. annuus and possible donor species, as well as phenotypic data from a common garden study. We found that although it is morphologically convergent with H. debilis, H. a. texanus has conflicting signals of introgression. Genome wide tests (Patterson's D and TreeMix) only found evidence of introgression from H. argophyllus (sister species to H. annuus and also sympatric), but not H. debilis, with the exception of one individual of 109 analysed. We further scanned the genome for localized signals of introgression using PCAdmix and found minimal but nonzero introgression from H. debilis and significant introgression from H. argophyllus in some populations. Given the paucity of introgression from H. debilis, we argue that the morphological convergence observed in Texas is probably from standing genetic variation. We also found that genomic differentiation in H. a. texanus is mostly driven by large segregating inversions, several of which have signatures of natural selection based on haplotype frequencies.
广泛分布物种中地理种族的起源尚不清楚。在得克萨斯州，长期以来人们一直认为向日葵的德克萨斯亚种通过与当地近缘种弱向日葵的基因渗入获得了其决定性的表型特征，但此前对这一假设的测试尚无定论。在这里，我们利用来自向日葵及其可能的供体物种整个分布范围的全基因组测序数据，以及一项共同园圃研究中的表型数据，来探究德克萨斯向日葵的起源。我们发现，尽管德克萨斯向日葵在形态上与弱向日葵趋同，但其基因渗入信号相互矛盾。全基因组测试（帕特森氏D和TreeMix）仅发现了来自银叶向日葵（向日葵的姐妹物种且同域分布）的基因渗入证据，而未发现来自弱向日葵的基因渗入证据，但在分析的109个个体中有一个除外。我们进一步使用PCAdmix扫描基因组以寻找局部基因渗入信号，发现来自弱向日葵的基因渗入极少但不为零，并且在一些种群中发现了来自银叶向日葵的显著基因渗入。鉴于来自弱向日葵的基因渗入很少，我们认为在得克萨斯州观察到的形态趋同可能源于现存的遗传变异。我们还发现，德克萨斯向日葵的基因组分化主要由大的分离倒位驱动，其中有几个基于单倍型频率具有自然选择的特征。
