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Speciation in Howea Palms Occurred in Sympatry, Was Preceded by Ancestral Admixture, and Was Associated with Edaphic and Phenological Adaptation.
Molecular Biology and Evolution ( IF 10.7 ) Pub Date : 2019-12-01 , DOI: 10.1093/molbev/msz166
Owen G Osborne 1, 2 , Adam Ciezarek 1 , Trevor Wilson 3 , Darren Crayn 4 , Ian Hutton 5 , William J Baker 6 , Colin G N Turnbull 7 , Vincent Savolainen 1, 6
Affiliation  

Howea palms are viewed as one of the most clear-cut cases of speciation in sympatry. The sister species Howea belmoreana and H. forsteriana are endemic to the oceanic Lord Howe Island, Australia, where they have overlapping distributions and are reproductively isolated mainly by flowering time differences. However, the potential role of introgression from Australian mainland relatives had not previously been investigated, a process that has recently put other examples of sympatric speciation into question. Furthermore, the drivers of flowering time-based reproductive isolation remain unclear. We sequenced an RNA-seq data set that comprehensively sampled Howea and their closest mainland relatives (Linospadix, Laccospadix), and collected detailed soil chemistry data on Lord Howe Island to evaluate whether secondary gene flow had taken place and to examine the role of soil preference in speciation. D-statistics analyses strongly support a scenario whereby ancestral Howea hybridized frequently with its mainland relatives, but this only occurred prior to speciation. Expression analysis, population genetic and phylogenetic tests of selection, identified several flowering time genes with evidence of adaptive divergence between the Howea species. We found expression plasticity in flowering time genes in response to soil chemistry as well as adaptive expression and sequence divergence in genes pleiotropically linked to soil adaptation and flowering time. Ancestral hybridization may have provided the genetic diversity that promoted their subsequent adaptive divergence and speciation, a process that may be common for rapid ecological speciation.

中文翻译:

Howea棕榈的形态发生在交感中,先于祖先混合物,并与Edaphic和物候适应有关。

Howea棕榈被认为是交联中最清晰的物种形成案例之一。姊妹物种Howea belmoreana和H. forsteriana是澳大利亚海洋豪勋爵岛的特有种,它们的分布重叠并且主要通过开花时间的差异生殖繁殖。但是,以前没有研究过澳大利亚大陆亲戚渗入的潜在作用,这一过程最近使同胞物种形成的其他例子受到质疑。此外,基于开花时间的生殖隔离的驱动因素仍然不清楚。我们对RNA-seq数据集进行了测序,该数据集全面采样了Howea及其近亲(Linospadix,Laccospadix),并在豪勋爵岛上收集了详细的土壤化学数据,以评估是否发生了次生基因流动,并研究了土壤偏好在物种形成中的作用。D统计分析强烈支持祖先豪亚经常与其大陆亲属杂交的情况,但这仅发生在物种形成之前。通过表达分析,选择的种群遗传和系统发育测试,确定了数个开花时间基因,这些基因证明了Howea种之间的适应性差异。我们发现响应土壤化学的开花时间基因中的表达可塑性,以及与土壤适应性和开花时间多效性相关的基因的适应性表达和序列差异。
更新日期:2019-07-18
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