The “Amazon tipping point” is a global change scenario resulting in replacement of upland terra‐firme forests by large‐scale “savannization” of mostly southern and eastern Amazon. Reduced rainfall accompanying the Last Glacial Maximum (LGM) has been proposed to have acted as such a tipping point in the past, with the prediction that terra‐firme inhabiting species should have experienced reductions in population size as drier habitats expanded. Here, we use whole‐genomes of an Amazonian endemic organism (Scale‐backed antbirds – Willisornis spp.) sampled from nine populations across the region to test this historical demography scenario. Populations from southeastern Amazonia and close to the Amazon–Cerrado ecotone exhibited a wide range of demographic patterns, while most of those from northern and western Amazonia experienced uniform expansions between 400 kya and 80–60 kya, with gradual declines toward 20 kya. Southeastern populations of Willisornis were the last to diversify and showed smaller heterozygosity and higher runs of homozygosity values than western and northern populations. These patterns support historical population declines throughout the Amazon that affected more strongly lineages in the southern and eastern areas, where historical “tipping point” conditions existed due to the widespread replacement of humid forest by drier and open vegetation during the LGM.

中文翻译：

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全基因组显示了第四纪晚期亚马逊特有雀形目鸟类种群规模变化和基因组多样性的对比趋势

“亚马逊临界点”是导致高地被取代的全球变化情景陆地亚马逊南部和东部地区的森林被大规模“稀树草原化”。过去，末次盛冰期（LGM）伴随的降雨量减少被认为是一个临界点，并预测：陆地随着干燥栖息地的扩大，居住物种的种群数量应该会减少。在这里，我们使用亚马逊特有生物的全基因组（鳞背蚁鸟 -威利索鸟spp.）从该地区的九个人口中抽样来测试这一历史人口统计情景。来自亚马逊东南部和亚马逊附近的种群–塞拉多生态交错带表现出广泛的人口模式，而大多数来自亚马逊流域北部和西部的人口在 400 基亚到 80-60 基亚之间均匀扩张，并逐渐下降至 20 基亚。东南部人口威利索鸟是最后多样化的群体，与西部和北部群体相比，杂合性更小，纯合性值更高。这些模式支持整个亚马逊地区历史上的人口下降，对南部和东部地区的谱系影响更大，这些地区存在历史“临界点”条件，因为在末次盛宴期间，潮湿的森林被干燥和开放的植被广泛取代。