Within and between population variation in inbreeding depression in the locally threatened perennial Scabiosa columbaria

Inbreeding depression plays a central role within the conservation genetics paradigm. Until now inbreeding depression is incorporated into models of population viability as a mean value (e.g. number of lethal equivalents) for all traits in a population. In this study of the locally threatened perennial plant species Scabiosa columbaria we investigated both the mean and the variance among families of inbreeding depression in eight life history traits for five natural populations varying in size from 300 to more than 120,000 individuals. Significant inbreeding depression was found in all populations and all traits. The mean inbreeding depression value per trait was never correlated to population size. Within each population, highly significant variation in inbreeding depression between families (VIFLID) was found. Per trait, families with inbreeding depression next to families with outbreeding depression were often found within the same population. Inbreeding depression at the family level was in many cases not correlated among traits and independent of correlations between traits themselves. VIFLID was negatively correlated with population size: in two traits these correlations were significant. The results underline that inbreeding depression is a complex, highly dynamic phenomenon. Models of viability should incorporate inbreeding depression distributions, with a trait specific mean and variance. Moreover, models of metapopulation dynamics should incorporate genotype quality as factor in colonization success.