Speciation in Howea palms occurred in sympatry, was preceded by ancestral admixture, and was associated with edaphic and phenological adaptation

Osborne, Owen G., Ciezarek, Adam, Wilson, Trevor, Crayn, Darren, Hutton, Ian, Baker, William J., Turnbull, Colin G.N., and Savolainen, Vincent (2019) Speciation in Howea palms occurred in sympatry, was preceded by ancestral admixture, and was associated with edaphic and phenological adaptation. Molecular Biology and Evolution, 36 (12). pp. 2682-2697.

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Abstract

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.

Item ID: 61303
Item Type: Article (Research - C1)
ISSN: 1537-1719
Keywords: introgression, speciation, sympatry
Copyright Information: Copyright The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.All rights reserved. For permissions, please e-mail: journals.permissions@oup.com
Funders: National Environment Research Council (NERC), Leverhulme Trust, European Research Council (ERC)
Date Deposited: 01 Jan 2020 07:35
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060311 Speciation and Extinction @ 70%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060310 Plant Systematics and Taxonomy @ 30%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960803 Documentation of Undescribed Flora and Fauna @ 20%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 80%
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