Mangaravite Érica, Vinson Christina C, Rody Hugo V S, Garcia Magali G, Carniello Maria A, Silva Roberta S, Oliveira Luiz O
Universidade Federal de Viçosa, Instituto de Biotechnologia Aplicada à Agropecuária 36570-000; Viçosa, MG, Brazil.
Universidade Federal do Pará, Faculdade de Ciências Biológicas 66075-110, Altamira, PA, Brazil.
Am J Bot. 2016 Feb;103(2):307-16. doi: 10.3732/ajb.1500370. Epub 2016 Feb 2.
We investigated how genetic diversity is distributed across the range of Cedrela fissilis, a tree species associated with seasonal neotropical forests, to gain insights into competing biogeographic scenarios that explain how disjunct distributions of these forests were shaped.
A total of 250 samples were sampled from 18 sites across the species' range in Brazil and eastern Bolivia and genotyped with 10 microsatellite loci. An array of complementary methods-F statistics, analyses of molecular variance (AMOVA), and clustering analyses-assessed genetic diversity, population differentiation, and structure.
Most of the genetic diversity (82.5%) was partitioned within populations, but about 12% was due to differences among groups of populations on either side of the Cerrado or located within the Cerrado; mean expected heterozygosity and mean observed heterozygosity were 0.821 and 0.704, respectively. The 250 samples were sorted into two Bayesian groups: one group for each side of the Cerrado. The populations showed varying levels of admixture, with the greatest admixture evident in populations located toward central Brazil.
In C. fissilis, genetic diversity is structured according to geography: the Atlantic range and the Chiquitano range each harbor a genealogical lineage. Interfertility and varying levels of admixture between lineages provide strong evidence that the lineages evolved under geographic, but not genetic, isolation. Admixture is of recent origin, owing to population expansion. Cedrela fissilis shares this dual pattern of distribution of genetic diversity with other phylogenetically unrelated taxa that are typically associated with seasonal forests.
我们调查了裂叶洋椿（Cedrela fissilis）——一种与新热带季节性森林相关的树种——的遗传多样性在其分布范围内是如何分布的，以深入了解相互竞争的生物地理情景，这些情景解释了这些森林的间断分布是如何形成的。
从巴西和玻利维亚东部该物种分布范围内的18个地点采集了总共250个样本，并用10个微卫星位点进行基因分型。一系列互补方法——F统计量、分子方差分析（AMOVA）和聚类分析——评估了遗传多样性、种群分化和结构。
大部分遗传多样性（82.5%）分布在种群内部，但约12%是由于塞拉多两侧或塞拉多内部种群组之间的差异；平均期望杂合度和平均观察杂合度分别为0.821和0.704。这250个样本被分为两个贝叶斯组：塞拉多两侧各一组。种群表现出不同程度的混合，在巴西中部的种群中混合程度最为明显。
在裂叶洋椿中，遗传多样性按地理结构分布：大西洋分布区和奇基塔诺分布区各自拥有一个谱系。谱系之间的可育性和不同程度的混合提供了有力证据，表明这些谱系是在地理隔离而非遗传隔离的情况下进化的。混合是近期起源的，这是由于种群扩张。裂叶洋椿与其他通常与季节性森林相关的系统发育上不相关的分类群共享这种遗传多样性的双重分布模式。
