Habitat fragmentation and the structure of genetic diversity within disjunct isolates of Anthericum ramosum L. (Anthericaceae) in Scandinavia

Abstract

The lilioid herb, Anthericum ramosum, occurs in four geographically-isolated regions (Sjælland, Skåne, Öland and Gotland) in Denmark and southern Sweden. We investigated allozyme variation at nine polymorphic loci in A. ramosum from 16 sites (33 populations) in the four regions. There was no clear overall geographic pattern of differentiation between the regions, but the southernmost Gotland and the Öland populations had similar allele frequencies, suggesting that they have had a common history. The total genetic diversity (Htot) was 0.458 and the between-region, site- and population components of diversity accounted, respectively, for 13%, 10% and 2% of the total diversity. The species is restricted to grassland habitats. Such habitats have become increasingly rare in the Sjælland and Skåne regions, where A. ramosum now has a highly fragmented distribution. Within three of the regions (Sjælland, Skåne and Öland) there was a negative relationship between the extent of grassland habitat and the between-site components of genetic diversity. Öland, with its extensive grassland habitats and low levels of population disjunction, showed little allelic differentiation between sites and the lowest between-site component of diversity (3%), suggesting that there is (or has been) extensive gene flow between sites. The between-site components of diversity were higher within Skåne (7%) and Sjælland (12%). The high within-region GST(25%) for the fourth region, Gotland, cannot be explained in terms of recent habitat disjunction but is, instead, interpreted in terms of the restricted distribution of limestone bedrock on Gotland and the fact that the southern and northern Gotland populations appear to have had different origins.