Phenotypic Plasticity of Size--Fecundity Relationships in Arabidopsis Thaliana

Abstract

1 The patterns of above ground allocation of meristems and resources are primary components of plant life history strategies, and are reflected in fecundity allocation, i.e. the observed relationship between plant size and fecundity. Phenotypic plasticity in fecundity allocation was investigated in the annual Arabidopsis thaliana. Individuals of each of three genotypes were grown under light, nutrient and pot volume gradients. Plant size (above ground vegetative mass excluding seeds) and fecundity (number of seeds) were measured for each individual at complete senescence. 2 In all combinations of three genotypes and three environmental factors, fecundity increased significantly with increasing plant size (P < 0.001). This increase was expressed through linear, quadratic, cubic and exponential relationships. Analyses of covariance with transformed data indicated that size-fecundity relationships were variable both between factors for individual genotypes and between genotypes within environmental factors. Hence not only size and fecundity, but also the relationship between size and fecundity can display phenotypic plasticity in this species. 3 Under light limitation some plants remained vegetative throughout their life span and it was therefore possible to identify a minimum size necessary to initiate production of reproductive meristems. However, some individuals of the same genotypes under nutrient limitation flowered and set seed although they were below this size limit. Hence, the minimum size for reproduction may also show phenotypic plasticity in A. thaliana. The observed variability in minimum size for reproduction and in fecundity allocation was not due to variation in developmental stage since all plants were harvested after fully completing their development. 4 Phenotypic plasticity in fecundity allocation and minimum size for reproduction implies that plants of the same size, in different environments, may not have the same fecundity, even if they are the same genotype. This plasticity has important implications in the interpretation of fitness estimates and in comparisons of life histories in plants.