An investigation into the evolutionary relationships of the North Island alpine ranunculus : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University, Palmerston North, New Zealand /
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Date
2006
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Massey University
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Abstract
Ranunculus nivicola is a member of the alpine Ranunculus (Section Pseudadonis), a group of 18 species that occupy distinct ecological habitats within mountainous environments of New Zealand and Australia. There are currently three species of alpine Ranunculus found in the North Island of New Zealand. Of those three species R nivicola is the only species endemic to the North Island. With a ploidy of 2n = 96, R. nivicola is the exception to the hexaploid state (2n = 48) of all other members of the alpine Ranunculus. It has been hypothesised that the elevated chromosome number in R. nivicola could be explained by a hybridisation event between the other two North Island species, R. insignis and R. verticillatus, with subsequent polyploidisation. The aim of the present study was to investigate the evolutionary history and habitat differences of the North Island species of Ranunculus through phylogenetic analyses of sequence data and the use of LENZ (Land Environments of New Zealand) data layers with geographic information systems. Nuclear ITS (ITS), chloroplast JSA
and trnL - trnF sequences were determined and analysed using median networks and maximum likelihood tree building. Positional data (from GPS grid points and herbarium records) for populations of each of the three species was used to query the LENZ database and extract information on environmental envelopes. The phylogenetic analyses indicate that R. verticillatus and R. insignis have different population histories, with range expansion occurring at different periods from the South to the North Island. Multiple events of dispersal between the South and the North Island could be inferred for R. verticillalus. However, only a single event of range expansion has occurred for R. insignis. A paucity of sequence variation among widely sampled accessions of R. nivicola may point to a recent (late Pleistocene-Holocene) origin for this allopolyploid. Interestingly, while R. nivicola nuclear ITS sequence is very similar to an extant genotype of R. verticillatus, its chloroplast sequence is intermediate between haplotypes shared by R. insignis and R. enjsii. There is no evidence for recurrent allopolyploid formation. Analyses of environmental data revealed that there were significant differences between the three species. R. insignis occupied the widest range of environments, with the environmental envelopes of R. verticillatus and R. nivicola occurring as subsets of the R. insignis envelope. It was also found that R. insignis could potentially occur in areas currently occupied exclusively by R. nivicola.
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Keywords
Phylogeny, Molecular aspects, New Zealand -- North Island, Ranunculus