Genetic variation of inbreeding depression among floral and fitness traits in Silene nutans.

The magnitude and variation of inbreeding depression (ID) within populations is important for the evolution and maintenance of mixed mating systems. We studied ID and its genetic variation in a range of floral and fitness traits in a small and large population of the perennial herb Silene nutans, using controlled pollinations in a fully factorial North Carolina II design. Floral traits and early fitness traits, that is seed mass and germination rate, were not much affected by inbreeding (δ<0.2). In contrast, ‘late’ fitness traits and multiplicative fitness suffered severely from inbreeding (δ>0.4). Lack of genetic correlations indicated that ID in floral, early and late traits is genetically decoupled. There was a trend that the smaller population was less affected by ID than the large one, although the differences were not significant for most traits. Hence, evidence for purging of deleterious alleles remains inconclusive in this study. Genetic variation in ID among paternal families was statistically significant in most floral and all seed traits, but not in late fitness traits. However, some paternal families had δ<0.5, even in the multiplicative fitness measure that suffered most from ID (δ=0.74), suggesting that the mixed mating system of S. nutans might be evolutionary stable. [ABSTRACT FROM AUTHOR]