Isozyme variation in Silene pratensis: a response to different environments

Abstract

The isozymes of nine enzyme systems were screened and the frequencies of the flavone glycosylating genes were determined in an outdoor experiment with 70 populations of European S. pratensis and an indoor experiment with 30 populations of the same species. Cluster analysis (using Ward's cluster criterion) were performed on all data sets. In the outdoor experiment, cluster analysis of the flavonoid data gave the same pattern that we obtained in an ealier survey of a larger set of populations and showed clearly that there are eight chemical races in European S. pratensis. No comparable geographic distributiion could be found in the isozyme data set, although the dendrogram showed two very clearly separated groups. The two groups represented the two years in which the populations were grown. This result indicates that isozyme variation in European S. pratensis is largely determined by environmental factors. Observations on changes in isozyme patterns during ontogeny and on differences between indoor and outdoor grown plants of the same F2 crosses confirm this. Differences in isozyme patterns can be caused by very small differencs in environment as is shown by the results of the indoor experiment, in which a slight gradient in environmental conditions was present in the greenhouses. The cluster analysis of the isozyme data from the indoor experiment revealed three distinct groups of populations that could be related to location within the greenhouses. As in the outdoor experiment, the dendrogram for the flavonoids gave the same geographic pattern as found with the earlier survey.