Genetics of mine invasions by Deschampsia cespitosa (Poaceae)

Abstract

Deschampsia cespitosa is a self-incompatible, tussock-forming, perennial grass with a scattered distribution in Ontario, primarily along the shores of the Great Lakes. In recent decades, D. cespitosa has colonized metal-contaminated sites in the mining regions of Sudbury and Cobalt. Isozyme variation in populations from contaminated and uncontaminated sites were compared to investigate the genetic consequences of mine invasion. Central Ontario populations are diploid (2n = 26); however, the complexity of electrophoretic patterns suggested that D. cespitosa is a diploidized tetraploid with considerable gene duplication. Innovative approaches were therefore required for quantitative assessment of isozyme variability within and among populations. Eighteen populations of D. cespitosa were assayed for variation at nine enzyme systems, representing 19 putative isozyme loci. Populations included eight from various uncontaminated habitats, five from mine sites around Sudbury, and five from Cobalt. Lower levels of diversity were evident in both Sudbury and Cobalt populations relative to uncontaminated populations. The results corroborated the prediction that colonization of contaminated habitats reduces levels of genetic variability, particularly where populations are recently established. Strong selection on mine sites will also compound stochastic loss of genetic diversity associated with colonization. The distribution of isozyme variation among populations of D. cespitosa was also used to infer colonization history. Cobalt and Sudbury populations were clearly differentiated by unique alleles at a number of enzyme systems, providing evidence for the independent origin of metal-tolerant populations in the two mining regions. Estimates of outcrossing frequency revealed no significant difference between a mine and an uncontaminated population; both populations exhibited high levels of outcrossing. Key words: colonization, mine invasion, genetic variation, Deschampsia cespitosa.