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

Genetic variation at alcohol dehydrogenase and phosphoglucoisomerase l oci in Bromus hordeaceus on the Baltic island of Oland shows substanti al spatial structuring among sites several km apart but also among plo ts 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 w ell-drained calcareous bedrock are interspersed with depressions conta ining 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 a nd the Pgi-1b-M allele was significantly associated with soil depth an d with the cover of mosses, lichens and grasses. These observations fr om field populations combined with results from previous studies of en zyme activity and differential individual fitness under experimental c onditions, support the suggestion that allelic variation at the Adh-1b locus in B. hordeaceus may be under selective control.