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Pleistocene divergence of two disjunct conifers in the eastern Australian temperate zone

Worth, JRP, Sakaguchi, S, Harrison, PA ORCID: 0000-0002-3502-0242, Bruniche-Olsen, A, Janes, JK, Crisp, MD and Bowman, DMJS ORCID: 0000-0003-2215-7685 2018 , 'Pleistocene divergence of two disjunct conifers in the eastern Australian temperate zone' , Biological Journal of the Linnean Society, vol. 125, no. 3 , pp. 459-474 , doi: 10.1093/biolinnean/bly127.

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Abstract

The eastern Australian temperate biota harbours many plants with fragmented geographic ranges distributed over 1000s of kilometres, yet the spatial genetic structure of their populations remains largely unstudied. In this study, we investigated genetic variation of the nuclear internal transcribed spacer (ITS) and chloroplast DNA sequences to disentangle the phylogeography of two widely distributed but highly fragmented eastern Australian fire-sensitive temperate conifers: Callitris oblonga (12 populations and 121 individuals) and C. rhomboidea (22 populations and 263 individuals). The three highly disjunct populations of C. oblonga all had unique chloroplast and ITS haplotypes consistent with the classification of these three populations as distinct subspecies. Molecular dating indicates that divergences of these populations occurred pre- to mid- Pleistocene (2.66 to 1.08 mya). Callitris rhomboidea showed greater diversity of chloroplast haplotypes which was strongly phylogeographically structured (Gst = 0.972), with haplotypes unique to specific geographic regions. ITS haplotype diversity was far higher than in C. oblonga with 38 haplotypes displaying high geographic structuring (Gst = 0.387) with many population-specific haplotypes. A phylogeographic break was identified between populations north and south of eastern Victoria dated at 0.43–0.47 mya. In both species, the strong genetic structuring of both chloroplast and ITS haplotypes provides evidence that their widespread ranges have resulted from long term persistence in low fire frequency refugia combined with poor dispersal. Any loss of populations due to increasing fire frequency or habitat loss is likely to result in a reduction of genetic diversity.

Item Type: Article
Authors/Creators:Worth, JRP and Sakaguchi, S and Harrison, PA and Bruniche-Olsen, A and Janes, JK and Crisp, MD and Bowman, DMJS
Keywords: chloroplast DNA, disjunct distribution, internal transcribed spacer, molecular dating, species districution modelling, temperate conifer
Journal or Publication Title: Biological Journal of the Linnean Society
Publisher: Blackwell Publishing Ltd
ISSN: 0024-4066
DOI / ID Number: 10.1093/biolinnean/bly127
Copyright Information:

© 2018 The Linnean Society of London

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