目标:在新热带南美洲东部,Cerrado,一个大的稀树草原植被,大西洋森林拥有高度的生物多样性,它们的栖息地彼此不同。生物群落具有内在的进化关系,可以归因于高度的血统交换,在某种程度上,它们之间有很大的接触区域。生态型的基因组研究,即适应不同栖息地的种群,可以成为研究生态差异的基因组特征的模型。这里,我们调查了树的两种生态型,一个来自塞拉多,另一个来自大西洋森林,在大西洋森林Cerrado的生态区有一个混合带。
方法:在两个生物群落及其过渡带中采样生态型。通过双消化限制性位点相关的DNA测序分析了该物种分歧的进化史。确定了杂交区的遗传结构和基因型组成。进行了基因型关联分析,并研究了推定选择下的基因座及其功能。
结果:发现两种生态型之间存在高度差异,在杂交区只发现了早期的杂种,暗示部分生殖障碍。未检测到Cerrado和大西洋森林之间的古代渗入。土壤和气候与斑疹生态型的遗传差异有关,并且发现离群位点与应激反应有关,有气孔和根发育和繁殖。
结论:高基因组,生态型之间的生态和形态生理学差异,再加上部分生殖隔离,表明生态型代表两个物种,应作为不同的进化谱系进行管理。我们建议应将森林物种重新评估并重新确定为脆弱物种。我们的结果提供了有关稀树草原和森林栖息地物种多样化的基因组机制以及新热带地区物种多样化的进化力的见解。
In eastern Neotropical South America, the Cerrado, a large savanna vegetation, and the Atlantic Forest harbour high biodiversity levels, and their habitats are rather different from each other. The biomes have intrinsic evolutionary relationships, with high lineage exchange that can be attributed, in part, to a large contact zone between them. The genomic study of ecotypes, i.e. populations adapted to divergent habitats, can be a model to study the genomic signatures of ecological divergence. Here, we investigated two ecotypes of the tree Plathymenia reticulata, one from the Cerrado and the other from the Atlantic Forest, which have a hybrid zone in the ecotonal zone of Atlantic Forest-Cerrado.
The ecotypes were sampled in the two biomes and their ecotone. The evolutionary history of the divergence of the species was analysed with double-digest restriction site-associated DNA sequencing. The genetic structure and the genotypic composition of the hybrid zone were determined. Genotype-association analyses were performed, and the loci under putative selection and their functions were investigated.
High divergence between the two ecotypes was found, and only early-generation hybrids were found in the hybrid zone, suggesting a partial reproductive barrier. Ancient introgression between the Cerrado and Atlantic Forest was not detected. The soil and climate were associated with genetic divergence in Plathymenia ecotypes and outlier loci were found to be associated with the stress response, with stomatal and root development and with reproduction.
The high genomic, ecological and morphophysiological divergence between ecotypes, coupled with partial reproductive isolation, indicate that the ecotypes represent two species and should be managed as different evolutionary lineages. We advise that the forest species should be re-evaluated and restated as vulnerable. Our results provide insights into the genomic mechanisms underlying the diversification of species across savanna and forest habitats and the evolutionary forces acting in the species diversification in the Neotropics.