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

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Title: Speciation in Howea palms occurred in sympatry, was preceded by ancestral admixture, and was associated with edaphic and phenological adaptation
Authors: Osborne, OG
Ciezarek, A
Wilson, T
Crayn, D
Hutton, I
Baker, WJ
Turnbull, CGN
Savolainen, V
Item Type: Journal Article
Abstract: Howea palms are viewed as one of the most clear-cut cases of speciation in sympatry. The sister species H. 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 dataset 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 hybridised 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 hybridisation may have provided the genetic diversity that promoted their subsequent adaptive divergence and speciation, a process that may be common for rapid ecological speciation.
Issue Date: 18-Jul-2019
Date of Acceptance: 8-Jul-2019
URI: http://hdl.handle.net/10044/1/71220
ISSN: 1537-1719
Publisher: Oxford University Press (OUP)
Journal / Book Title: Molecular Biology and Evolution
Copyright Statement: This paper is embargoed until 12 months after publication.
Sponsor/Funder: Commission of the European Communities
Natural Environment Research Council (NERC)
The Leverhulme Trust
Funder's Grant Number: 233190
NE/M015742/1
RF-2016-373/2
Keywords: 0604 Genetics
0603 Evolutionary Biology
0601 Biochemistry and Cell Biology
Evolutionary Biology
Publication Status: Accepted
Embargo Date: 2020-07-18
Appears in Collections:Faculty of Natural Sciences



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