title: Ecological speciation in sympatric palms: 2. Pre- and post-zygotic isolation.
abstract: We evaluated reproductive isolation in two species of palms (Howea) that have evolved sympatrically on Lord Howe Island (LHI, Australia). We estimated the strength of some pre- and post-zygotic mechanisms in maintaining current species boundaries. We found that flowering time displacement between species is consistent across in and ex situ common gardens and is thus partly genetically determined. On LHI, pre-zygotic isolation due solely to flowering displacement was 97% for Howea belmoreana and 80% for H. forsteriana; this asymmetry results from H. forsteriana flowering earlier than H. belmoreana and being protandrous. As expected, only a few hybrids (here confirmed by genotyping) at both juvenile and adult stages could be detected in two sites on LHI, in which the two species grow intermingled (the Far Flats) or adjacently (Transit Hill). Yet, the distribution of hybrids was different between sites. At Transit Hill, we found no hybrid adult trees, but 13.5% of younger palms examined there were of late hybrid classes. In contrast, we found four hybrid adult trees, mostly of late hybrid classes, and only one juvenile F1 hybrid in the Far Flats. This pattern indicates that selection acts against hybrids between the juvenile and adult stages. An in situ reciprocal seed transplant between volcanic and calcareous soils also shows that early fitness components (up to 36 months) were affected by species and soil. These results are indicative of divergent selection in reproductive isolation, although it does not solely explain the current distribution of the two species on LHI.
authors.affiliation: Department of Life Sciences, Imperial College London, Silwood Park Campus, Ascot, UK.
authors.forename: H
authors.initials: H
authors.lastname: Hipperson
authors.affiliation: Department of Life Sciences, Imperial College London, Silwood Park Campus, Ascot, UK.
authors.forename: L T
authors.initials: LT
authors.lastname: Dunning
authors.affiliation: Royal Botanic Gardens, Kew, Richmond, UK.
authors.forename: W J
authors.initials: WJ
authors.lastname: Baker
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield, UK.|Sven Lovén Centre for Marine Sciences, Tjärnö, University of Gothenburg, Stromstäd, Sweden.
authors.forename: R K
authors.initials: RK
authors.lastname: Butlin
authors.affiliation: Lord Howe Island Museum, Lord Howe Island, NSW, Australia.
authors.forename: I
authors.initials: I
authors.lastname: Hutton
authors.affiliation: Department of Life Sciences, Imperial College London, Silwood Park Campus, Ascot, UK.|Royal Botanic Gardens, Kew, Richmond, UK.
authors.forename: A S T
authors.identifier: 0000-0001-6589-754X
authors.initials: AS
authors.lastname: Papadopulos
authors.affiliation: Department of Life Sciences, Imperial College London, Silwood Park Campus, Ascot, UK.
authors.forename: C M
authors.initials: CM
authors.lastname: Smadja
authors.affiliation: Royal Botanic Gardens and Domain Trust, Sydney, NSW, Australia.
authors.forename: T C
authors.initials: TC
authors.lastname: Wilson
authors.forename: C
authors.initials: C
authors.lastname: Devaux
authors.affiliation: Department of Life Sciences, Imperial College London, Silwood Park Campus, Ascot, UK. v.savolainen@imperial.ac.uk.|Royal Botanic Gardens, Kew, Richmond, UK. v.savolainen@imperial.ac.uk.
authors.forename: V
authors.initials: V
authors.lastname: Savolainen
mesh_terms: D000818:Animals; D028023:Arecaceae; D001315:Australia; D005838:Genotype; D006824:Hybridization, Genetic; D060047:Reproductive Isolation; D061350:Sympatry
keywords: flowering; hybridization; phenology; post-zygotic; pre-zygotic