Departamento de Genética, Ecologia e Evolução, Universidade Federal de Minas Gerais, CP, Belo Horizonte, Brazil.
Departamento de Botânica, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
Ann Bot. 2020 Jun 19;126(1):191-203. doi: 10.1093/aob/mcaa066.
Dimorphandra wilsonii Rizzini, a critically endangered and protected tree, has a restricted distribution in the ecotone between the Cerrado and the Atlantic Forest in south-eastern Brazil. In this area, it co-occurs with D. mollis Benth., a common tree from the Cerrado, and D. exaltata Schott., a rare tree from the Atlantic Forest. Previous studies of D. wilsonii indicated heterozygosity excess at the individual level. Field observation of some intermediate phenotypes between D. wilsonii and both congeners suggests hybridization of D. wilsonii with D. mollis and/or D. exaltata. Here, we tested the hypothesis that D. wilsonii may have originated from hybridization between D. exaltata and D. mollis. We also performed cytogenetic analysis to examine if the heterozygosity excess could be explained by polyploidy in D. wilsonii.
We evaluated the genetic diversity and population structure of D. wilsonii using 11 nuclear simple sequence repeats (SSRs) genotyped in 152 individuals sampled across the taxon's range. We performed comparative genetic analyses using overlapping SSR markers between D. wilsonii and previously published SSR data in D. mollis and D. exaltata to subsequently perform a series of allelic comparisons, multivariate and Bayesian analysis.
Our results suggest that D. wilsonii individuals are most likely to correspond to F1 hybrids between D. exaltata and D. mollis. Cytogenetic analysis indicated that D. wilsonii is diploid with the same chromosome number as D. mollis (2n = 2x = 28).
Our study raises questions about the taxonomic status and the evolutionary future of D. wilsonii. We suggest that the conservation and management strategy for D. wilsonii should be revised and that it should take into account both parental Dimorphandra species in the ecotone, with special emphasis on the threatened D. exaltata. Finally, this study highlights the value of genetic information for the design of conservation strategies.
Dimorphandra wilsonii Rizzini 是一种濒危保护树种，仅分布于巴西东南部热带稀树草原与大西洋森林的生态过渡带。在该地区，它与常见的热带稀树草原树种 D. mollis Benth. 和稀有的大西洋森林树种 D. exaltata Schott. 共存。先前对 D. wilsonii 的研究表明，个体水平存在杂合子过剩。对 D. wilsonii 与两个近缘种之间的一些中间表型的野外观察表明，D. wilsonii 与 D. mollis 和/或 D. exaltata 发生了杂交。在这里，我们检验了 D. wilsonii 可能是由 D. exaltata 和 D. mollis 杂交产生的假设。我们还进行了细胞遗传学分析，以检验 D. wilsonii 的杂合子过剩是否可以用多倍体解释。
我们使用 11 个核简单序列重复（SSR）标记对 152 个个体进行基因分型，评估了 D. wilsonii 的遗传多样性和种群结构。我们使用重叠的 SSR 标记对 D. wilsonii 与先前发表的 D. mollis 和 D. exaltata 的 SSR 数据进行了比较遗传分析，随后进行了一系列等位基因比较、多元分析和贝叶斯分析。
我们的结果表明，D. wilsonii 个体最有可能是 D. exaltata 和 D. mollis 杂交产生的 F1 杂种。细胞遗传学分析表明，D. wilsonii 是二倍体，与 D. mollis 的染色体数相同（2n = 2x = 28）。
我们的研究对 D. wilsonii 的分类地位和进化前景提出了质疑。我们建议修订 D. wilsonii 的保护和管理策略，同时考虑生态过渡带中的双亲种 Dimorphandra 物种，特别强调受威胁的 D. exaltata。最后，本研究强调了遗传信息在保护策略设计中的价值。
