title: How sympatric is speciation in the Howea palms of Lord Howe Island?
abstract: The two species of the palm genus Howea (Arecaceae) from Lord Howe Island, a minute volcanic island in the Tasman Sea, are now regarded as one of the most compelling examples of sympatric speciation, although this view is still disputed by some authors. Population genetic and ecological data are necessary to provide a more coherent and comprehensive understanding of this emerging model system. Here, we analyse data on abundance, juvenile recruitment, pollination mode and genetic variation and structure in both species. We find that Howea forsteriana is less abundant than Howea belmoreana. The genetic data based on amplified fragment length polymorphisms markers indicate similar levels of variation in the two species, despite the estimated census population size of H. belmoreana being three times larger than that of H. forsteriana. Genetic structure within species is low although some weak isolation by distance is detectable. Gene flow between species appears to be extremely limited and restricted to early-generation hybrids - only three admixed individuals, classified as F2s or first generation backcrosses to a parental species, were found among sampled palms. We conclude that speciation in Howea was indeed sympatric, although under certain strict definitions it may be called parapatric.
authors.affiliation: Imperial College London, Silwood Park, Ascot, Berkshire, UK.
authors.forename: Wiesław
authors.initials: W
authors.lastname: Babik
authors.forename: Roger K
authors.initials: RK
authors.lastname: Butlin
authors.forename: William J
authors.initials: WJ
authors.lastname: Baker
authors.forename: Alexander S T
authors.initials: AS
authors.lastname: Papadopulos
authors.forename: Matthieu
authors.initials: M
authors.lastname: Boulesteix
authors.forename: Marie-Charlotte
authors.initials: MC
authors.lastname: Anstett
authors.forename: Christian
authors.initials: C
authors.lastname: Lexer
authors.forename: Ian
authors.initials: I
authors.lastname: Hutton
authors.forename: Vincent
authors.initials: V
authors.lastname: Savolainen
mesh_terms: D054458:Amplified Fragment Length Polymorphism Analysis; D028023:Arecaceae / Q000145:classification / Q000235:genetics*; D001315:Australia; D018744:DNA, Plant / Q000235:genetics; D051456:Gene Flow; D049810:Genetic Speciation; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D010802:Phylogeny; D054817:Pollination; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D018744:DNA, Plant