Size-dependent sex allocation in Cynoglossum officinale for different genotypes under uniform favourable conditions

Field observations showed that small plants often have lower female investment than large plants. Field-collected data do not elucidate, however, whether this pattern is an inherent effect of size or if it is caused by poorer environmental quality of sites where small plants are growing and/or by genotypic differences between small and large plants. Therefore, the relationship between plant mass and flower and seed production was measured under favourable conditions using full-sibs and clones of Cynoglossum officinale. The aim of this study is to determine if the pattern of size-dependent gender was maintained if both small and large plants are grown under favourable conditions, and if this pattern is consistent among genotypes. Over all genotypes, smaller plants produced more flowers per unit plant mass compared to large plants. On the other hand, seed production per unit plant mass did not significantly differ between plants of different sizes. As a result, the number of seeds per flower increased with increasing plant mass, large plants produced 1.5 times more seeds per flower compared to small plants. Thus small plants emphasize the male side, whereas large plants emphasize the female side of production. We conclude that, even under favourable environmental conditions, all genotypes examined maintain size-dependent sex allocation(SDS). When analysed separately, we found no genetic variation in seed production among genotypes (full sibs and clones). In contrast, genotypes differed significantly in flower production. Neither the number of seeds per gram plant mass nor per flower differed significantly among genotypes. In our experiment no evidence was found for a negative genetic correlation between flower production per unit plant mass and seed production per unit plant mass.