GENETIC-STRUCTURE AND ALLOZYME-MICROHABITAT ASSOCIATIONS IN BROMUS-HORDEACEUS

Genetic variation at alcohol dehydrogenase and phosphoglucoisomerase loci in Bromus hordeaceus on the Baltic island of Oland shows substantial spatial structuring among sites several km apart but also among plots within sites on a scale less than ten M. Oland habitats occupied by B. hordeaceus consist of a fine-scale mosaic in which thin soils on well-drained calcareous bedrock are interspersed with depressions containing deeper soil and subject to seasonal water logging. Among sites, the frequency of the Adh-1b-S allele was significantly associated with soil depth and with the cover of mosses and of grasses. The frequency of the Pgi-1b-F allele was significantly associated with soil depth and the Pgi-1b-M allele was significantly associated with soil depth and with the cover of mosses, lichens and grasses. These observations from field populations combined with results from previous studies of enzyme activity and differential individual fitness under experimental conditions, support the suggestion that allelic variation at the Adh-1b locus in B. hordeaceus may be under selective control.