Plant-fungal coevolution and speciation on a remote oceanic island

自从达尔文的开创性工作以来，我们对物种起源（物种形成）的理解发生了很大的变化。然而，有一个方面被忽略了，那就是微生物在推动物种形成中所起的作用。在此，我们提出了一种物种起源的新机制，即植物-菌根联合的共同进化分歧增加了局部适应并导致物种形成的完成。虽然众所周知，物种可以因山脊或海洋等地理障碍而分化，但种群也可以在没有地理隔离的情况下面对基因流动而分裂，例如通过对栖息地或资源的专业化。在这种情况下，植物与微生物的共生关系可能特别强大，可以同时促进局部适应和生殖隔离，从而导致物种形成。我们将重点研究塔斯曼海一个偏远岛屿Lord Howe岛特有的一对姐妹植物物种，以及它们与丛枝菌根真菌的相互作用。利用Lord Howe岛植物区系的系统发育、核生物学和生态学数据，Supervisor Savolainen先前证明，事实上，在某些情况下，基因流动的物种形成可能很频繁，可能占LHI特有植物物种的五分之一（PNAS108, 13188- 993, 2011）。这些例子，如Coprosma和Metrosideros，将为本博士研究。我们假设土壤和土壤微生物影响了祖先种群的局部适应，从而导致开花时间的差异，并最终促进了物种形成。不同水平的菌根定植和在植物寄主和菌根关联中共同调控的基因表达可能导致占据不同环境（土壤、海拔梯度等）的不同种群的出现。我们将使用宏基因组学和RNA-seq结合田间/温室实验来验证关键假设。提出的工作有可能带来对物种形成机制和共同进化如何促进物种分化的激烈反思。这项提议的工作将揭示一些在进化中最被忽视的假设，例如微生物如何驱动植物物种形成，以及微生物组和植物多样性之间的联系。鉴于植物-菌根共生的广泛性，它们在作物生产中的重要性，以及土壤和植物多样性在生态系统功能中的突出地位，我们的研究也将在应用生态学和农业领域产生深远的影响，而不仅仅是进化生物学。

Our understanding of how species originate (speciation) has changed considerably since Darwin's seminal work. One aspect, however, that has been ignored is the role that microbes can play in driving speciation. Here, we propose a new mechanism for the origin of species, whereby coevolutionary divergence in plant-mycorrhizal associations increases local adaptation and leads to the completion of speciation. While it is well known that species can diverge due to geographic barriers such as mountain ridges or oceans, populations can also split in the face of gene flow without geographic isolation, for example through specialisation to habitats or resources. In this context, symbiotic associations that plants have with microbes may be particularly powerful in simultaneously facilitating local adaptation and reproductive isolation leading to speciation.We will focus on pairs of sister species of plants endemic to Lord Howe Island, a remote island in the Tasman sea, and their interactions with arbuscular mycorrhizal fungi. Using phylogenetic, karyological, and ecological data for the flora of Lord Howe Island, Supervisor Savolainen previously demonstrated that speciation with gene flow may, in fact, be frequent in some instances and could account for one in five of the endemic plant species of LHI (PNAS108, 13188-93, 2011). These examples, such as Coprosma and Metrosideros, will be studied for this PhD. We hypothesise that soil and soil microbes have affected local adaptation of the ancestral populations, which in turn led to differences in flowering time, and ultimately promoted speciation. Differing levels of mycorrhizal colonisation and gene expression coregulated in plant host and mycorrhizal associations may have led to the emergence of distinct populations occupying different environments (soil, altitudinal gradient, etc). We will test key hypotheses using metagenomics and RNA-seq combined with field/greenhouse experiments. The proposed work has the potential to bring drastic rethinking about the mechanisms of speciation and how coevolution contributes to species divergence. The proposed work will unravel some of the most neglected hypotheses in evolution, such as how microbes can drive plant speciation, and hence the link between microbiome and plant diversity. Given the widespread nature of plant-mycorrhizal symbioses, their importance in crop production, and the prominence of soil and plant diversity in ecosystem functioning, our research will also havefar-reaching impact in applied ecology and agriculture, beyond evolutionary biology.