Departamento de Genética, Instituto de Biociências, Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Distrito de Rubião Junior s/n, Botucatu, SP, Brazil.
Ann Bot. 2010 Oct;106(4):627-36. doi: 10.1093/aob/mcq151. Epub 2010 Aug 10.
Species delimitation can be problematic, and recently diverged taxa are sometimes viewed as the extremes of a species' continuum in response to environmental conditions. Using population genetic approaches, this study assessed the relationship between two Casearia sylvestris (Salicaceae) varieties, which occur sympatrically and allopatrically in the landscape of south-east Brazil, where intermediate types are also found.
In total, 376 individuals from nine populations in four different ecosystems were sampled, and nine microsatellite markers were used to assess the relative effects of the ecosystems and varieties on the distribution of genetic diversity among populations of this species.
As a by-product of this study, several PCR products with more than two alleles were observed. The possibility that extra bands represent non-specific amplification or PCR artefacts was discarded by sequencing a sample of these bands. We suggest that (partial) genome duplication in C. sylvestris most probably explains this phenomenon, which may be a key factor in the differentiation of the two taxa, as it was markedly more frequent in one of the varieties. AMOVA indicated that approx. 22 % of the total genetic diversity was found between the two varieties. Bayesian analysis identified varieties and ecosystems as evolutionary units, rather than the individual populations sampled.
The results are in agreement with field observations and support the recognition of two varieties, as well as documenting the occurrence of hybridization between them.
物种划分可能存在问题，最近分化的分类群有时被视为物种对环境条件响应的连续体的极端。本研究采用种群遗传方法，评估了巴西东南部景观中两种同域和异域分布的野扇花（杨柳科）变种之间的关系，该地区也存在中间类型。
共从四个不同生态系统的九个种群中采集了 376 个个体，使用九个微卫星标记来评估生态系统和变种对该物种种群间遗传多样性分布的相对影响。
作为本研究的副产品，观察到了几个具有两个以上等位基因的 PCR 产物。通过对这些条带的一部分进行测序，排除了额外条带代表非特异性扩增或 PCR 假象的可能性。我们认为，野扇花中的（部分）基因组复制很可能解释了这一现象，这可能是两种分类群分化的关键因素，因为在其中一种变种中更为频繁。AMOVA 表明，约 22%的总遗传多样性存在于两种变种之间。贝叶斯分析将变种和生态系统识别为进化单位，而不是采样的个体种群。
结果与野外观察一致，支持识别两个变种，并记录了它们之间杂交的发生。
