Laboratório de Genética & Biodiversidade, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, GO, Brasil.
Instituto Federal Goiano, Rio Verde, GO, Brasil.
Ann Bot. 2018 Nov 30;122(6):973-984. doi: 10.1093/aob/mcy060.
Spatial distribution of species genetic diversity is often driven by geographical distance (isolation by distance) or environmental conditions (isolation by environment), especially under climate change scenarios such as Quaternary glaciations. Here, we used coalescent analyses coupled with ecological niche modelling (ENM), spatially explicit quantile regression analyses and the multiple matrix regression with randomization (MMRR) approach to unravel the patterns of genetic differentiation in the widely distributed Neotropical savanna tree, Hancornia speciosa (Apocynaceae). Due to its high morphological differentiation, the species was originally classified into six botanical varieties by Monachino, and has recently been recognized as only two varieties by Flora do Brasil 2020. Thus, H. speciosa is a good biological model for learning about evolution of phenotypic plasticity under genetic and ecological effects, and predicting their responses to changing environmental conditions.
We sampled 28 populations (777 individuals) of Monachino's four varieties of H. speciosa and used seven microsatellite loci to genotype them.
Bayesian clustering showed five distinct genetic groups (K = 5) with high admixture among Monachino's varieties, mainly among populations in the central area of the species geographical range. Genetic differentiation among Monachino's varieties was lower than the genetic differentiation among populations within varieties, with higher within-population inbreeding. A high historical connectivity among populations of the central Cerrado shown by coalescent analyses may explain the high admixture among varieties. In addition, areas of higher climatic suitability also presented higher genetic diversity in such a way that the wide historical refugium across central Brazil might have promoted the long-term connectivity among populations. Yet, FST was significantly related to geographic distances, but not to environmental distances, and coalescent analyses and ENM predicted a demographical scenario of quasi-stability through time.
Our findings show that demographical history and isolation by distance, but not isolation by environment, drove genetic differentiation of populations. Finally, the genetic clusters do not support the two recently recognized botanical varieties of H. speciosa, but partially support Monachino's classification at least for the four sampled varieties, similar to morphological variation.
物种遗传多样性的空间分布通常由地理距离（距离隔离）或环境条件（环境隔离）驱动，特别是在第四纪冰川等气候变化情景下。在这里，我们使用合并分析结合生态位模型（ENM）、空间显式分位数回归分析和随机化多矩阵回归（MMRR）方法，揭示了广泛分布的新热带稀树草原树，Hancornia speciosa（夹竹桃科）的遗传分化模式。由于其高度的形态分化，该物种最初由 Monachino 分为六个植物变种，最近被 Flora do Brasil 2020 识别为只有两个变种。因此，H. speciosa 是一个很好的生物学模型，可以了解遗传和生态效应下表型可塑性的进化，并预测它们对环境条件变化的反应。
我们对 Monachino 的 H. speciosa 的四个变种的 28 个种群（777 个个体）进行了采样，并使用七个微卫星位点对它们进行了基因分型。
贝叶斯聚类显示有五个不同的遗传群体（K = 5），Monachino 的变种之间存在高度的混合，主要存在于物种地理范围的中心地区的种群之间。Monachino 的变种之间的遗传分化低于变种内种群之间的遗传分化，种内近交率较高。合并分析表明，中央塞拉多地区的种群之间存在高度的历史连通性，这可能解释了变种之间的高度混合。此外，气候适宜度较高的地区也表现出较高的遗传多样性，因此，横跨巴西中部的广泛历史避难所可能促进了种群之间的长期连通性。然而，FST 与地理距离显著相关，但与环境距离无关，合并分析和 ENM 预测了准稳定的人口动态情景。
我们的研究结果表明，人口历史和距离隔离，而不是环境隔离，驱动了种群的遗传分化。最后，遗传聚类不支持 H. speciosa 的最近被认可的两个植物变种，而是至少部分支持 Monachino 的分类，至少对于四个采样的变种来说是这样，类似于形态变异。
