Evolutionary Processes in Populations of Copper Tolerant Agrostis tenuis Sibth

Populations of Agrostis tenuis Sibth. were collected from disused copper mines and nearby ordinary pasture in North Wales and Ireland. These populations were sampled as tillers and as seed. Tests for copper tolerance on these populations showed that: a) All populations growing on copper mines have copper tolerance. b) Populations taken from uncontaminated sites removed by as little as 15 1/2 meters from contaminated sites with tolerant populations show absence of copper tolerance. The reverse situation is equally true. c) The character of copper tolerance has high heritability. d) There is evidence of gene flow into mine populations, and also for genetic segregation within such populations. By contrast there is very little evidence of gene flow into non-tolerant populations. This can be explained in terms of the spatial relationships of the populations concerned. e) There is strong evidence for the operaation of natural selection in favor of copper tolerance on copper contaminated soils, and against it on uncontaminated soils, maintaining the status quo. f) The differences found between seedling and adult data for the same population, point to the dangers and values of using plants grown from collections of spontaneous seed material in population studies.