GENETIC-VARIATION IN RURAL AND URBAN POPULATIONS OF EPIPACTIS-HELLEBORINE (L) CRANTZ (ORCHIDACEAE) IN BRITAIN

Genetic variation in Epipactis helleborine in the British Isles was as sessed using starch gel electrophoresis of isozymes; 273 individuals w ere sampled from 13 populations and examined for genetic variation usi ng eight enzyme systems encoded for by 13 loci. Overall, 46% of the lo ci examined were polymorphic, with an average of 1.69 alleles per locu s. Within populations, a mean of 33% of the loci were polymorphic, wit h a mean number of 1.46 alleles per locus. Levels of genetic variation were compared between urban and well established rural populations to assess the genetic consequences of colonization of the urban sites. T he average levels of genetic variation detected in urban populations w ere lower than that found in rural populations. although there was a m uch greater range of variation among the urban populations. Large urba n populations actually have patterns of variation similar to rural pop ulations and show evidence of multiple founders. This indicates that t he high dispersibility of Epipactis seeds can in some cases overcome t he predicted loss of genetic variation associated with founder effects during colonization. Small urban populations, however, show significa ntly lower levels of genetic variation compared with these large urban populations and the rural populations, and it seems likely that this is attributable to single founding events and/or genetic drift. (C) 19 97 The Linnean Society of London.