VARIATION IN FITNESS-RELATED CHARACTERS AMONG SMALL AND LARGE POPULATIONS OF SALVIA-PRATENSIS

1 The threatened perennial Salvia pratensis is restricted to a few isolated populations in the Netherlands, which vary in size from 10 to 1500 flowering individuals. Small populations are known to have significantly lower allozyme diversity than the large populations, probably as a consequence of genetic erosion. We test the prediction that small populations of this species will have lower fitness than large populations. 2 Seed from two small and two large populations was grown in a common environment. There was significant variation among populations in mean seed weight, seed size, percentage germination, plant biomass and growth, and in number of flowers per individual, but none of these differences could be attributed to differences in population size or level of allozyme diversity. 3 Differences in seed set, seed size and seedling size were probably largely influenced by nongenetic maternal effects. Differences in plant biomass at harvest after 5 months were independent of initial differences in seedling size, indicating that characters later in plant life are probably largely independent of maternal effects. 4 The present results, together with the known lack of difference in population growth rate and inbreeding depression in large and small populations, suggest that the small populations are in an early phase of the genetic erosion process, where their allozyme diversity has decreased, but where the quantitative genetic variation underlying fitness traits has not (yet) been affected. 5 Environmental differences and population history may be no less important than allozyme diversity for predicting differences in fitness among populations. Genetic erosion may be a major cause of viability problems in the future.