The aim of this study was to research the ecology and genetics of Cirsium dissectum and to
discuss the implications of the results for its conservation. The ecology of C. dissectum
was described through a review of the literature. Site characteristics, plant communities
and reproductive biology were investigated by examining 22 populations throughout the
British Isles. Microsatellite genetic markers were used to investigate levels of genetic
diversity within and between these populations. Within populations, relationships between
genetic diversity, population size, fitness and habitat quality (concentrating on soil
nutrients and vegetation structure) were explored using multiple regression and structural
equation modelling. Differentiation between populations was examined by comparing
rnicrosatellite markers with morphological traits and this was supplemented by a crossing
experiment that investigated the effects of inbreeding and outbreeding.
This study showed that C. dissectum was a clonal species with a mixed mating
system. Previous research had suggested that clonal propagation was the dominant form of
reproduction but this study showed that sexual reproduction was important in this species,
as levels of genotypic diversity were high. There were interactions between population
size, genetic diversity, plant fitness and habitat quality. Smaller populations of C.
dissectum had lower genetic diversity and this subsequently reduced plant fitness. Higher
levels of bare soil and phosphorus were related to higher levels of genetic diversity; bare
soil may provide establishment gaps for seedlings and clonal offspring, while phosphorus
may encourage flowering and/or seedling survival.
Populations of C. dissectum showed high levels of genetic differentiation and
strong isolation by distance using microsatellite genetic markers. Both microsatellite
genetic markers and morphological traits revealed geographical structuring between
populations, but this was less pronounced using the morphological traits. Plants in Ireland
showed higher levels of morphological differentiation compared to Britain. C. dissectum
showed strong, early acting inbreeding depression when plants were selfed and a trend
towards outbreeding depression when genetically distant populations were crossed.
Populations of C. dissectum should be conserved throughout the geographical range
of the species in the British Isles. Sites should be managed so that habitat heterogeneity is
maintained, enabling C. dissectum rosettes to flower and to maintain bare soil for seedling
establishment. Habitat restoration should use seed collected from a number of local
populations of the same habitat.
Date of Award | 2007 |
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Original language | English |
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Awarding Institution | |
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The Ecology and Genetics of Cirsium dissectum (L.) Hill in the British Isles and Implications for its Conservation
de Vere, N. (Author). 2007
Student thesis: PhD