Demography and genetic diversity in Tradescantia occidentalis (commelinaceae)
Genetic diversity has rarely been the focus of study in species at risk in Canada. Tradescantia occidentalis is one of 157 species listed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC 2005a). This species is nationally threatened due to the limited number of populations, their geographic isolation from each other and from the main distribution in the United States of America, and habitat loss. The National Recovery Team for Plants at Risk in the Prairie Provinces and the Alberta Western Spiderwort Recovery Team have called for research into the habitat requirements, demography, and genetic diversity of T. occidentalis in Canada. As a result, this study was designed to address the following objectives: 1) to conduct an inventory of the Canadian populations, 2) to investigate intra- and interpopulation genetic diversity in Tradescantia occidentalis, and 3) to provide recommendations for the conservation management of this species. Information on demography and plant communities in Tradescantia occidentalis habitats indicated that the numbers of individuals in the Saskatchewan and Manitoba populations were similar to previous surveys; however, the Alberta population was significantly larger in number than prior estimates, indicating population growth. Taxonomic lists were prepared for each province in habitats with and without T. occidentalis. Community types, as separated by RA analysis, differed by province and not by association with T. occidentalis. Euphorbia esula, an invasive species in Canada, was observed in the Saskatchewan and Manitoba populations but was absent in Alberta. Using amplified fragment length polymorphisms (AFLPs), genetic diversity was assessed at the intra- and interpopulation levels. Relatively low levels of intrapopulation variation were observed in Saskatchewan and Alberta, while higher levels were found in Manitoba. Gene flow via pollen or propagule transfer may account for higher genetic diversity among the closely situated Manitoba populations. The lack of correlation between dendrogram topology and geographic distribution suggests panmixia in all populations. Levels of intrapopulation diversity were low to moderate depending on primer combination used, indicating that populations are isolated within each province. Information on population demography and genetic diversity are important within a conservation context. The large number of individuals within each population and the perceived increase in some populations suggest that the existing populations of Tradescantia occidentalis are relatively stable. Although levels of genetic diversity are low in Saskatchewan and Alberta compared to Manitoba, it appears that all populations are adapted to their local environments based on their apparent size and stability. The most viable conservation strategy for this species is in situ protection. This should include controlling invasive plant species, monitoring grazing, and preventing further habitat fragmentation. Ex situ methods must also be explored. Transplantation of individuals from one population to the next may not be a successful conservation strategy due to the moderate level of population differentiation. Alternatively, it is recommended that a seed bank from each population be implemented in case of a drastic population decline.
population demography, endangered plant species, Tradescantia occidentalis, genetic diversity
Master of Science (M.Sc.)