Evolution of the south-western Pacific genus Melicytus (Violaceae): evidence from DNA sequence data, cytology and sex expression
A. D. Mitchell A , P. B. Heenan B E , B. G. Murray C , B. P. J. Molloy B and P. J. de Lange DA University of Otago, Christchurch, PO Box 4345, Christchurch Mail Centre, Christchurch 8140, New Zealand.
B Allan Herbarium, Landcare Research, PO Box 40, Lincoln 7640, New Zealand.
C School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand.
D Research, Development and Information, Department of Conservation, Private Bag 68908, Newton, Auckland 1145, New Zealand.
E Corresponding author. Email: heenanp@landcareresearch.co.nz
Australian Systematic Botany 22(3) 143-157 https://doi.org/10.1071/SB08042
Submitted: 11 September 2008 Accepted: 12 March 2009 Published: 10 June 2009
Abstract
Phylogenetic analyses of nuclear DNA external transcribed spacer (ETS) and chloroplast DNA trnL–trnF markers were undertaken to reconstruct the evolutionary history of the South Pacific genus Melicytus. Bayesian analyses of the ETS sequence data produced a phylogenetic tree with several well supported groups, including clades comprising: (1) species from Australia, Tasmania and Lord Howe Island; (2) the Norfolk Island M. latifolius and New Zealand off-shore island M. novae-zelandiae subsp. novae-zelandiae; (3) the large-leaved M. ramiflorus complex; (4) M. fasciger and M. micranthus; and (5) M. obovatus and allies from the Cook Strait region. Phylogenetic analysis of trnL–trnF sequence data also retrieved some of these groups although, in general, was not as well resolved. The relationships of M. lanceolatus are equivocal, as in the ETS phylogeny it is sister to a clade comprising the large-leaved tree species M. fasciger and M. ramiflorus complex and the small-leaved M. micranthus, whereas in the trnL–trnF phylogeny it is sister to a clade of small-leaved shrub species such as M. alpinus and M. crassifolius. Several biogeographic patterns are evident, with dispersal to the west from New Zealand, to Australia, involving small-leaved shrub species. Dispersal to the north from New Zealand, to Norfolk Island and Fiji, involves large-leaved tree species. The sex expression is documented for all named species and undescribed entities, with these being either hermaphroditic or dioecious. When sex expression is mapped onto the phylogeny, the hermaphroditic system is inferred to have evolved from the dioecious system. New chromosome counts are presented for M. angustifolius (2n = 64) and M. dentatus (2n = 32), and earlier counts of 2n = 64 are confirmed for M. crassifolius and M. alpinus. An additional 17 counts are provided for two natural hybrids and several undescribed entities from Australia and New Zealand. The polyploid chromosome number of 2n = 64 occurs most frequently in small-leaved divariate plants with hermaphroditic flowers. When chromosome numbers are plotted onto the phylogeny it is inferred that high polyploids (e.g. 2n = 64) and small-leaved shrubs have evolved from large-leaved trees with functional diploid (e.g. 2n = 32) chromosome numbers.
Acknowledgements
We thank Adrian Paterson (CHEARS Marsden) for discussion in regard to the molecular clock methods; David Purcell for propagating and growing the cultivated plants; Alex Buchanan (HO) for field assistance in obtaining material of Melicytus angustifolius in Tasmania; Neville Walsh for helpful discussion; staff from Australian National Botanic Garden Canberra, Mt Tomah Botanic Garden, New Zealand Department of Conservation, and landholders in Australia and NZ for permission to collect plant material; Christine Bezar, Dr Rob Smissen and Dr Henry Connor for comments on the draft manuscript; Dr Jacqui Keenan for kindly sharing her laboratory space at the University of Otago, Christchurch; and herbarium staff at AK, CANB, CHR, MEL, WELT. Funds for this research were provided to ADM by the Marsden Fund and to PBH by the New Zealand Foundation for Research Science and Technology through the Defining New Zealand’s Land Biota OBI.
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