Abstract
In Belgium, at the north-western margin of its geographical range, Silene nutans is a rare species, which has evolved a silicicolous (Si) and a calcicolous (Ca) ecotype, with contrasting morphometric traits. Genetic diversity and population genetic structure were examined for seven allozyme loci in 16 Si and 18 Ca populations (a total of 567 individuals). High genetic variation was found at both the ecotypic and population level, and no significant correlation was found between population size and any measure of genetic variation. The maintenance of high levels of genetic diversity in small, marginal populations might be explained by the perennial, long-lived life form and the outcrossing breeding system of the species. Additionally, low FST-values suggested that efficient gene flow was occurring within both ecotypes. Genetic distance measures and cluster analysis using upgma on the distance matrix revealed that the populations were differentiated according to their ecotypic property in two distinct gene pools. It is argued that the congruence of allozymic and morphometric differentiation between edaphic races is unusual for an outcrossing species. This finding, together with previous observations of isolating mechanisms between ecotypes, strongly suggests that incipient speciation is occurring within Silene nutans at the margin of its geographical range.
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van Rossum, F., Vekemans, X., Meerts, P. et al. Allozyme variation in relation to ecotypic differentiation and population size in marginal populations of Silene nutans. Heredity 78, 552–560 (1997). https://doi.org/10.1038/hdy.1997.86
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DOI: https://doi.org/10.1038/hdy.1997.86
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