Geographic differentiation and population history in Silene dioica and S. hifacensis: variation in chloroplast DNA and allozymes
Abstract: In this thesis I used allozymes and PCR-RFLP analysis of chloroplast DNA (cpDNA) to investigate geographic differentiation within the widespread Silene dioica (L.) Clairv. (Caryophyllaceae) and the narrowly-distributed S. hifacensis Rouy ex Willk., (a Spanish endemic). In an investigation of allozyme variation in Nordic S. dioica, multivariate analysis of variation at eight polymorphic loci revealed a division into overlapping groups of populations, one in the northwestern part and another in the southwestern part. Analysis of cpDNA variation revealed a similar but less diffuse NE-SW pattern of variation. These results suggest that the postglacial colonization of Fennoscandia by S. dioica involved immigration of populations from two main directions: from the east or northeast and the south. Distribution of three common cpDNA haplotypes in European populations of S. dioica suggested refugial areas for the species in the Mediterranean region and further to the east. A fourth common haplotype dominated in northern and eastern Fennoscandia and appears to have had an eastern origin. The occurrence of a suite of rarer haplotypes found in S and E Europe may represent lineages from one or several Mediterranean refugia that have spread and persisted within the montane belt to the S and E of the high Alps but which have failed to spread extensively to N and W Europe. Some haplotypes may have their origin in hybridization with the closely-related species, Silene latifolia. The allozyme and cpDNA analysis of S. hifacensis show that this species is characterized by low levels of allelic variation, a high ratio of between- to within-population variation and a mosaic pattern of between-population differentia-tion in both allozymes and cpDNA haplotypes. The results also indicate that the cpDNA haplotype in the majority of the Ibiza populations differs from those in the two investigated mainland populations. The distribution of genetic variation in S. hifacensis is discussed in terms of population history, dispersal and, speculatively, in terms of anthropogenic manipulation.
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