Arbuscular mycorrhizal fungi promote coexistence and niche divergence of sympatric palm species on a remote oceanic island

• Published in: The New phytologist 2018-02, Vol.217 (3), p.1254-1266
• Main Authors: Osborne, Owen G., De‐Kayne, Rishi, Bidartondo, Martin I., Hutton, Ian, Baker, William J., Turnbull, Colin G. N., Savolainen, Vincent
• Format: Article
• Language: English
• Subjects: Adaptation; Arbuscular mycorrhizas; Arecaceae - microbiology; Biodiversity; Biological evolution; Calcareous soils; Coexistence; Divergence; DNA Barcoding, Taxonomic; ecological speciation; Ecosystem; edaphic adaptation; Fitness; Fungi; Genes; Geography; Germination; Howeia belmoreana; Howeia forsteriana; Interactions; Interspecific; Islands; Microbiomes; mycorrhizae; Mycorrhizae - growth & development; Mycorrhizae - physiology; Natural selection; Niches; Oceanic islands; Oceans and Seas; Palmae; Principal Component Analysis; Reproductive fitness; Seedlings - physiology; Sibling species; Soil; Soil investigations; Soil Microbiology; Soil types; Speciation; Species; Species Specificity; Sterilization; symbiosis; Sympatric populations; sympatric speciation; Sympatry - physiology; Tradeoffs; Volcanic soils
• ISSN: 0028-646X; 1469-8137; 1469-8137
• DOI: 10.1111/nph.14850

Microbes can have profound effects on their hosts, driving natural selection, promoting speciation and determining species distributions. However, soil-dwelling microbes are rarely investigated as drivers of evolutionary change in plants. We used metabarcoding and experimental manipulation of soil microbiomes to investigate the impact of soil and root microbes in a well-known case of sympatric speciation, the Howea palms of Lord Howe Island (Australia). Whereas H. forsteriana can grow on both calcareous and volcanic soils, H. belmoreana is restricted to, but more successful on, volcanic soil, indicating a trade-off in adaptation to the two soil types. We suggest a novel explanation for this trade-off. Arbuscular mycorrhizal fungi (AMF) are significantly depleted in H. forsteriana on volcanic soil, relative to both H. belmoreana on volcanic soil and H. forsteriana on calcareous soil. This is mirrored by the results of survival experiments, where the sterilization of natural soil reduces Howea fitness in every soil–species combination except H. forsteriana on volcanic soil. Furthermore, AMF-associated genes exhibit evidence of divergent selection between Howea species. These results show a mechanism by which divergent adaptation can have knock-on effects on host–microbe interactions, thereby reducing interspecific competition and promoting the coexistence of plant sister species.