It has been hypothesized that the Araucaria Forest in southern Brazil underwent expansions in the past, driven either by human groups or by climate fluctuations of the Holocene and Pleistocene. Fossil pollen records of the Paraná pine Araucaria angustifolia, a dominant tree in that forest, provide some insights into when those may have occurred. Still, the timing of those expansions has never been estimated. To infer past range shifts and shed light on their main drivers, we employed next-generation DNA sequencing (ddRADseq), machine learning, and a comprehensive database of fossil pollen records into a study of historical demographic inference and paleo-distribution modeling of the Paraná pine. We found that A. angustifolia comprises two populations expanding at different times: one in the Mantiqueira mountain chain, the other in the southern Brazilian plateau. The southern population began to expand during the Last Glacial Period ~ 70 kya, long before human arrival in South America. Still, genetic analyses support that humans later impacted this population, resulting in lower genetic diversity, higher inbreeding, and high levels of gene flow over large distances with a weak pattern of isolation-by-distance. It is possible this resulted from human influence on seed dispersal and germination on the southern Brazilian plateau. The Mantiqueira population, in contrast, expanded only recently (~ 3 kya). This timing coincides with Holocene climatic changes and human settlements established further south, although, to date, there is little archeological evidence of human impact in the Mantiqueira. In addition, multitemporal species distribution models built from a combination of present-day and pollen records infer a range expansion of the Araucaria Forest during glacial times until the cold humid HS1 event (~ 16 kya), when the forest was most widespread, with no evidence of glacial refugia. The combination of genomic and spatial analyses suggests that both human and climatic controls played a role in the dynamics of the Araucaria Forest.

中文翻译：

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评估历史气候和早期人类群体对南美洲东部南洋杉森林的影响


据推测，巴西南部的南洋杉森林在过去经历过扩张，要么是受人类群体的推动，要么是受全新世和更新世气候波动的推动。巴拉那松南洋杉（该森林中的主要树种）的化石花粉记录为了解这些情况可能发生的时间提供了一些见解。尽管如此，这些扩张的时间从未被估计过。为了推断过去的范围变化并阐明其主要驱动因素，我们采用了下一代 DNA 测序 (ddRADseq)、机器学习和化石花粉记录综合数据库来研究巴拉那州的历史人口统计推断和古分布模型松树。我们发现狭叶珊瑚由两个在不同时间扩张的种群组成：一个在曼蒂凯拉山脉，另一个在巴西南部高原。南部人口在末次冰期期间开始增加约 70 基亚，远早于人类到达南美洲。尽管如此，遗传分析仍然支持人类后来影响了这个种群，导致遗传多样性较低、近亲繁殖程度较高、远距离基因流动水平较高，且距离隔离模式较弱。这可能是由于人类对巴西南部高原种子传播和发芽的影响造成的。相比之下，曼蒂凯拉人口最近才开始增加（约 3 基亚）。这一时间恰逢全新世气候变化和人类定居点在更南边建立，尽管迄今为止，几乎没有考古证据表明人类对曼蒂凯拉的影响。 此外，结合当今和花粉记录建立的多时相物种分布模型推断，南洋杉森林在冰期期间范围扩大，直到寒冷潮湿的 HS1 事件（约 16 kya），此时森林最广泛，没有冰川避难所的证据。基因组和空间分析的结合表明，人类和气候控制在南洋杉森林的动态中发挥了作用。