Format: ORAL

Vincent Savolainen1, Kyle Macleod1, Martin Bidartondo1, Colin Turnbull1, Roger Butlin2, Ian Sanders3, Ian Hutton4

1 Imperial College London, London, UK 2 University of Sheffield, Sheffield, UK 3 University of Lausanne, Lausanne, Switzerland 4 Lord Howe Island Museum, Lord Howe Island, Australia

Our understanding of how species originate (speciation) has changed considerably since Darwins 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, using one of the most compelling examples of speciation in the face of gene flow as our model system: The Howea palms of Lord Howe Island. 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 two sister species of palms (Howea), endemic to Lord Howe Island, a remote island in the Tasman sea, and their interactions with arbuscular mycorrhizal fungi. Howea palms represent the dominant vegetation on the island. The speciation scenario for Howea involves adaptation to different soils, volcanic rocks and calcareous deposits, and associated fitness trade-offs. We hypothesise that soil and soil microbes have affected local adaptation of the ancestral palm population, which in turn led to differences in flowering time, and ultimately promoted speciation. Differing levels of mycorrhizal colonisation and gene expression co-regulated in Howea and mycorrhizal associations may have led to the emergence of distinct forms of Howea populations occupying different soils. We will test these key hypotheses using metagenomics and RNA-seq combined with long-term field experiments on Lord Howe Island.