Evolution of Dendrocolaptes platyrostris (Aves: Furnariidae) between the South American open vegetation corridor and the Atlantic forest

The open vegetation corridor of South America is a region dominated by savanna biomes. It contains forests, i.e. riverine forests, that may act as corridors for rainforest specialist between the open vegetation corridor and its neighboring biomes, the Amazonian and Atlantic forests. A prediction for this scenario is that populations of rainforest specialists in the open vegetation corridor and in the forested biomes show no significant genetic divergence. We addressed this hypothesis by studying plumage and genetic variation of the Planalto woodcreeper Dendrocolaptes platyrostris Spix (1824) (Aves: Furnariidae), a forest specialist that occurs in both the open habitat and in the Atlantic forest. Our questions are: (1) is there any evidence of genetic continuity between populations of the open habitat and the Atlantic forest? and (2) is plumage variation congruent with patterns of neutral genetic structure or with ecological factors related to habitat type? We used cytochrome b and mtDNA control region sequences to show that D. platyrostris is monophyletic and that presents substantial intraspecific differentiation. We found two areas of plumage stability: one associated to Cerrado and the other associated to southern Atlantic Forest. Multiple Mantel tests showed that most of the plumage variation followed transition of habitats but not phylogeographic gaps, suggesting that selection may be related to the evolution of the species plumage. Results were not compatible with the idea that forest specialist in the open vegetation corridor and in the Atlantic forest are linked at the population level because birds from each region were not part of the same genetic unit. Divergence in the presence of gene flow across the ecotone between both regions might explain our results. Also, our findings indicate that the southern Atlantic forest may have been significantly affected by Pleistocene climatic alteration, but that those events did not cause local extinction of most taxa, as occurred in other regions of the globe where forests were significantly affected by global glaciations. Finally, our results neither supported subspecies nor regions of stability of plumage as species.

南美洲开阔植被廊道（open vegetation corridor）是一片以稀树草原生物群系（savanna biomes）为主的区域。该区域内包含河岸林（riverine forests），此类河岸林可作为雨林特化物种在开阔植被廊道与相邻的亚马孙森林（Amazonian forest）、大西洋森林（Atlantic forest）之间的迁移廊道。针对该情景的预测认为，开阔植被廊道与森林生物群系内的雨林特化物种种群之间未呈现显著的遗传分化。本研究以高原砍林鸟（Planalto woodcreeper，*Dendrocolaptes platyrostris* Spix, 1824）（鸟纲（Aves）：灶鸟科（Furnariidae））为研究对象，该物种为森林特化物种，同时分布于开阔生境与大西洋森林中。本研究旨在解答两个问题：（1）开阔生境与大西洋森林的种群间是否存在遗传连续性？（2）羽色变异是否与中性遗传结构模式相符，抑或与生境类型相关的生态因子相关？本研究通过细胞色素b（cytochrome b）与线粒体DNA控制区（mtDNA control region）序列分析，证实高原砍林鸟为单系群（monophyletic），且存在显著的种内分化（intraspecific differentiation）。研究发现两处羽色稳定区域：一处与塞拉多稀树草原（Cerrado）相关，另一处与南大西洋森林相关。多重曼特尔检验（Mantel test）结果显示，多数羽色变异与生境过渡相关，而非与系统地理空缺（phylogeographic gaps）相关，这表明选择作用可能与该物种的羽色演化有关。本研究结果与“开阔植被廊道与大西洋森林内的森林特化物种种群间存在种群水平关联”这一观点不符，因为来自两个区域的个体并不属于同一遗传单元。两区域生态交错带（ecotone）内存在基因流情况下的分化现象，或可解释本研究的结果。此外，研究结果表明南大西洋森林曾受更新世（Pleistocene）气候剧变的显著影响，但此类事件并未像全球其他受全球冰川作用显著影响的森林区域那样，导致多数类群的局部灭绝。最后，本研究结果既不支持将羽色稳定区域划分为亚种（subspecies），也不支持将其作为独立物种。