GENETIC DIVERSITY IN LEAVENWORTHIA POPULATIONS WITH DIFFERENT INBREEDING LEVELS

Levels of neutral genetic diversity within and between populations wer e compared between outcrossing (self-incompatible) and inbreeding popu lations in the annual plant genus Leavenworthia. Two taxonomically ind ependent comparisons are possible, since self-incompatibility has been lost twice in the group of species studied. Within inbred populations oft. uniflora and L. crassa, no DNA sequence variants were seen among the alleles sampled, but high diversity was seen in alleles from popu lations of the outcrosser L. stylosa, and in self-incompatible L. cras sa populations. Diversity between populations was seen in all species. Although total diversity values were lower in the sets of inbreeding populations, between-population values were as high, or higher, than t hose in the outcrossing taxa. Possible reasons for these diversity pat terns are discussed. As the effect of inbreeding appears to be a great er than twofold reduction in diversity, we argue that some process suc h as selection for advantageous mutations, or against deleterious muta tions, or bottlenecks occurring predominantly in the inbreeders, appea rs necessary to account for the findings. If selection for advantageou s mutations is responsible, it appears that it must be some form of lo cal adaptive selection, rather than substitution of alleles that are a dvantageous throughout the species. This is consistent with the findin g of high between-population diversity in the inbreeding taxa.