GENETIC-VARIATION AND OUTCROSSING RATE IN RELATION TO POPULATION-SIZE IN GENTIANA-PNEUMONANTHE L

The amount of genetic variation in the rare perennial herb Gentiana pneumonanthe L. was determined to explore its relation to population size. Differences in isozyme variation between maternal plants and their offspring were used to investigate the relationship between population size and outcrossing rate. In 25 populations in The Netherlands, differing in size from 1 to more than 50,000 flowering individuals, 16 allozyme loci were analyzed on leaves of maternal plants and offspring grown in a greenhouse Population sire was significantly positively, correlated with the proportion of polymorphic loci, but only marginally with heterozygosity and the mean effective number of alleles. Most of the studied populations were characterized by a complete absence of rare alleles, and F-statistics suggest relatively high levels of genetic differentiation among populations and thus a lour level of gene flow Leaf samples (maternal) were mostly, in Hardy-Weinberg equilibrium, while several offspring samples showed an excess of homozygotes, which suggests selection favoring heterozygotes. Because most small populations consist only of adult survivors from formerly larger populations, this may partly explain the absence of a clear relationship between genetic variation of the maternal plants and population size. A significant positive correlation was found between the level of cross fertilization and population size. From these results, we conclude that to some degree, small populations have a reduced level of genetic variation, while their present isolation in nature reserves has resulted in a very limited interpopulational gene flow level Atf,resent, a higher level of inbreeding in small populations contributes to a further loss of genetic variation and may also result in reduced off spring fitness.