Genotypic variation in fecundity allocation in Arabidopsis thaliana

1. Genetic variability in the relationship between plant size and fecundity (fecundity allocation) was investigated in 10 inbred lines (genotypes) of Arabidopsis thaliana. For each genotype, a range of plant sizes was established by planting seeds at various densities. Plant size (above-ground biomass excluding seeds), fecundity (number of seeds produced), and percentage germination of seeds were recorded for 20 individuals representative of the range of plant sizes displayed for each genotype as a result of the density treatments. 2. There was a significant (P < 0.001) positive relationship between plant size and fecundity for all genotypes. Size--fecundity regressions were primarily linear within the range investigated and the slopes differed significantly between genotypes. The y intercepts were either significantly positive or not different from zero. Seed viability generally did not depend on the number of seeds produced. 3. Genotypes with relatively large maximum plant sizes had relatively low fecundities. This trade-off is consistent with r/K-selection theory; such genotypes are regarded as having a 'K-type strategy'. There is no basis for predicting, however, that such a 'strategy' will confer superior fitness in contexts of competition. 4. The rank-order of fecundity was not consistent for all plant sizes. Individual genotypes with greater-than-average fecundity when relatively large in size tended to have lower-than-average fecundity when smaller, whilst the converse was true for genotypes having lower-than-average fecundity when relatively large. 5. The results indicate that absolute allocation to fecundity at a given plant size, and the variation in fecundity allocation across different sizes, can vary significantly at the level of the genotype in this species. This may be an important component in defining differences in fitness between individuals in the context of competition.