| Summary: | This thesis examines population genetic structure and migration indices of an Antarctic endemic lichen Buellia frigida as well as algal selectivity of the lichens Buellia frigida, Umbilicaria aprina and Umbilicaria decussata in the Ross Sea Region of Antarctica. My aim was to determine where current populations may have originated (i.e. ancient or recent introductions to Antarctica) and if the level of algal selectivity potentially affects colonisation. Chapter 2 reviews historical climate change in Antarctica, particularly in the Ross Sea Region, and introduces the basic characteristics of lichens. It also outlines how molecular analyses of lichen can aid in determining the genetic structure of populations and add to the growing data set which highlights sites in the Ross Sea Region (e.g. Dry Valleys) as glacial refugia. To examine population differentiation between populations in this region it was necessary to develop polymorphic markers capable of delineating individuals. Chapter 3 focuses on the development of five microsatellite markers for this purpose. The initial data for these microsatellites suggested they were suitable for individual genotyping and characterization of B. frigida population structure being mycobiont specific with a high degree of polymorphism. A method of decreasing inhibiting factors present in lichen cells is also provided. In Chapter 4 regional genetic differentiation was revealed by an analysis using microsatellite markers developed in Chapter 3 over 11 populations in five regions of the Ross Sea Region. The identification of three populations with high allelic richness and sites of high dispersal indicated three regions as putative refugia (Terra Nova Bay, Dry Valleys and Beardmore Glacier). Terra Nova Bay has not previously been highlighted putatively as refugia. Limited mixing between adjacent geographical areas (such as the Dry Valleys and Ross Island) was identified, with migration likely to be influenced by wind currents. The photobionts of the lichens Buellia frigida, Umbilicaria aprina and Umbilicaria decussata were examined using ITS rDNA sequence analysis in chapter 5. This identified that over a latitudinal gradient of roughly 10˚, there was a single haplotype present in the majority (>95%) of samples. This haplotype was nearly identical to haplotypes from as far afield as Svalbard showing a consistency in photobiont selection over a very wide geographical range and may be micro-climate specific. Other haplotypes present were specific to single geographical areas, and mutation may play the major role in this. Collectively, these findings suggest that despite potentially high dispersal of propagules, populations of lichen species in the Ross Dependency show differentiation among locations and are potentially limited in their dispersal to different habitats. This may be the result of high selectivity for the photobiont. I conclude that lichen populations in the Ross Sea Region have originated from ancient, refugial populations rather than being populated via recent dispersal from northern continents. Dispersal within this region is likely to be restricted by ice-covered areas and relichenisation is potentially limited to particular photobiont strains which are suited to the micro-climatic conditions found in this region. In order to minimise the consequences of anthropological disturbance, we recommend the continued protection of areas (e.g. Dry Valleys) housing high lichen and photobiont diversity.
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