Molecular genetics and the conservation of plants : two case studies
The Convention on Biodiversity (CBD) signed at the 1992 Earth summit in Rio formally recognized biodiversity at the habitat, species, and genetic levels. For species and habitat biodiversity there is a well-established set of frameworks under which conservation programmes are constructed and delivered. From a genetic biodiversity perspective, however, there is no clear consensus on how best it should be measured, or how conservation programmes should be implemented. The major reasons for conserving intra-specific genetic biodiversity can be summed up under two inter-related themes, (1) Protecting a broad spectrum of genetic biodiversity, and (2) Maintaining evolutionary fitness and adaptive variation. This thesis takes a case-study approach and explores the issues surrounding these themes for conservation strategies in two angiosperm species: Saxifraga hirculus and Lathyrus japonicus. 1) Protecting a broad spectrum of genetic biodiversity: This section of the thesis considered the evidence for major intra-specific genetic races in Saxifraga hirculus and the spatial distribution of its genetic biodiversity. Variation in Saxifraga hirculus chloroplast DNA was assessed in order to gain information on the biogeography of the British populations in the context of the wider European gene pool, and also to compare this with populations from Alaska and Colorado. In a European context, British popUlations have a high level of chloroplast diversity (three haplotypes) and contain a highly divergent lineage that was previously unsuspected. Seven haplotypes were found in total from 17 popUlations in Europe with marked inter-population differentiation (FST = 0.92). Higher diversity and lower popUlation differentiation was detected in Alaska (33 haplotypes /12 populations; FST = 0.46). Since most popUlations in Europe had unique haplotypes it is not possible to track migration routes or pinpoint refugia for the European popUlations, but the much higher diversity in Alaska compared to Europe indicates that the Beringia region may have acted as a refugium for this species throughout the Pleistocene. This highlights the importance of Alaska for the conservation of intra-specific genetic biodiversity in this species. (2) Evolutionary fitness and adaptive variation: To assess the relationship between population size, genetic variation, morphological variation and fitness, genetic studies were undertaken on populations of Lathyrusjaponicus. Eleven populations of L. japonicus were examined for variation using nine microsatellite loci. The populations show genetic isolation by distance across the distribution of the species in Britain, although isolation by distance breaks down when only the range centre populations are considered. There was no relationship between population size or isolation and genetic variation, with some small and/or isolated populations having high diversity, and large and/or range centre populations having low diversity. There was, however, a significant difference in the inbreeding coefficient of adult versus seedling plants. The heterozygosity of adult plants sampled in the field was significantly higher than seedlings grown in cultivation, indicating a survival advantage for heterozygotes. Significant differences were found between populations for seed weight, number of seeds per pod, number of pods per cluster, and leaf shape of L. japonicus individuals in the field. For seedlings grown in common conditions significant differences were found in leaf shape, pigmentation, and dry weight after two season's growth. Morphological and genetic differentiation were well matched in this species, and gave similar signals. Seedlings from Carnoustie (Scotland) grew much more vigorously in cultivation in Edinburgh than seedlings sourced from English populations, indicating local adaptation. However no significant relationship was found between any fitness associated traits or morphological variation with genetic variation, in spite of the heterozygote advantage revealed by the genetic data. The results from both research themes are discussed highlighting the difficulties in equating patterns of genetic marker variation to traits likely to be of evolutionary and ecological relevance.