A population genetics approach to species delimitation in the genus Selliera (Goodeniaceae) : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University, Palmerston North, New Zealand
Currently there is only one internationally recognised species of Selliera, Selliera
radicans. In New Zealand, three species have been described based on morphology
and geographic location although there is disagreement about whether these
actually constitute different species. Selliera rotundifolia is distinguished from S.
radicans by rounder leaves and a preferred dune habitat compared to the estuary
habitat of S. radicans. Selliera microphylla is distinguished from S. radicans by a
smaller size and inland location. However, S. microphylla reverts to a size similar
to S. radicans when grown in the same environment, but a single chromosome
count for S. microphylla on the Central Volcanic Plateau is 2n=56. Both S.
rotundifolia and S. radicans have chromosome counts of 2n=16. Species
delimitation is important in biology, conservation, and evolutionary studies but
remains a difficult task. I applied a population genetics approach combined with
morphological analysis of leaves and existing karyotype data to determine the
species boundaries within Selliera.
Microsatellite markers are ideal for use in population genetics due to the higher
mutation rate, genotyping ease and their co-dominant nature. No microsatellite
markers previously existed for use in Selliera. In this study, next generation
sequencing was used to develop microsatellite markers for Selliera. From 8,101
independent sequence contigs, 107 microsatellite loci were detected and primer
pairs designed for these. Forty-three of these primer pairs were chosen to be
screened and nine of these were reliably amplifiable and polymorphic. These nine
markers were genotyped over 618 samples from Selliera comprising the three
Populations within all three described species showed high differentiation and S.
radicans was variable for population structure. Leaf morphological analyses
suggested there was a distinct difference between the three species. Microsatellite
data revealed two genetic clusters in S. microphylla which clustered into the North
Island and South Island populations. Two genetic clusters were also observed in S.
rotundifolia which each clustered with different S. radicans populations suggesting
round leaves may have had multiple origins. Hybridization was observed at one
sympatric site between S. radicans and S. rotundifolia and apparent reproductive
isolation for S. rotundifolia was observed at another site.
These results suggest that the South Island S. microphylla population may be an
inland variant of S. radicans which may continue to diverge if it remains isolated,
while the North Island populations should retain the S. microphylla name due to the
2n=56 chromosome count, geographic isolation and genetic distinction although
this needs further review. There is evidence of reproductive isolation for S.
rotundifolia at one of the sympatric sites suggesting this is a distinct species but it
appears round leaves may have had multiple origins so may not be suitable to
describe the species according to the lineage species concept. This study provides
insights into the population structure within and between the described species and
has identified interesting areas of future study.