Abstract
Alpine environments are highly variable with different selective pressures compared to lower altitude habitats. The alpine zone in New Zealand was formed in isolation and displays a range of unusual floral characteristics compared to those seen overseas, such as the over dominance of small white flowers. New Zealand has 17 species of Euphrasia L. 1, all of which are hemiparasite and short-lived. The study species, Euphrasia dyeri Wettst, is endemic to New Zealand and has white flowers, but in contrast to the majority of New Zealand flora, E.dyeri also has purple flowers on the same plant. The aim of this thesis was to investigate the role of flower colour and its relationship to pollinator preferences, floral rewards, floral morphology, and breeding system. This thesis also investigated aspects of seed germination and genetic divergence between populations. Observations were made of pollinator visitation to purple and white flowers and flower colour change after pollination at two alpine locations in Otago, the Blue Mountains and the Pisa Range. Timing of pollen release and stigmatic receptivity was determined as well as nectar production and pollen type. Measurements of floral dimensions were made to compare white and purple flowers between five different alpine sites. Self-compatibility and autogamy were investigated via bagging and hand or cross pollination experiments. Seeds from these experiments were collected in order to trial cultivation in-vitro. Genetic divergence between populations was assessed using the internal transcribed spacer region of nuclear ribosomal DNA. This study found that flowers are protogynous with extended stigmatic receptivity, but stigmas are only receptive when flowers are white. Flower size increases as flowers age and flower colour changes from white to purple after pollination. The species is self-compatible and also capable of autogamous selfing because anther growth with flower aging brings the anthers in contact with the stigma. Seed is set from self-pollinated and cross-pollinated flowers. Pollinators consistently favour white flowers which also contain detectable amounts of nectar. Purple flowers did not contain nectar. Thus In E.dyeri flower colour appears to be a cue that pollinators use to identify if a flower has reward. Germination of seeds in the hemiparasitic genus Euphrasia is a two step process where the radicle grows then a connection to the host is formed, subsequently low germination rates are observed during in-vitro cultivation. Germination in this study was only successful when seeds were initially surface sterilized and sown with two hosts – ryegrass and lettuce. The evolutionary trees produced from sequences show that it is most likely that there are two different groups within E.dyeri species but these are not related to geographic or altitudinal groups, nor to morphological variation among populations. In light of these findings it is thought that a mixed breeding system with flower colour change as a cue to pollinators could be an adaptation to sporadic visitation by pollinators. Genetic analysis shows that E.dyeri branches into two separate groups. This knowledge about the breeding systems, germination and genetics in Euphrasia aids understanding of evolutionary pressures and speciation in the New Zealand alpine flora and may increase our ability to conserve species that are endangered or threatened elsewhere in the world.
1 All nomenclature follows the Landcare Research online database Ngā Tipu Aotearoa – New Zealand Plants unless it is stated otherwise (http://nzflora.landcareresearch.co.nz/).