Evolutionary significance of genotypic variation in developmental reaction norms for a perennial grass under competitive stress
- Cite this article as:
- Cheplick, G. Evolutionary Ecology (2003) 17: 175. doi:10.1023/A:1023057024776
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The developmental reaction norm (DRN) represents the set of ontogenetic trajectories that can be produced by a genotype exposed to different environmental conditions. Genetic variation in the DRN for growth traits and in the patterns of biomass allocation is critical to phenotypic evolution in heterogeneous environments. The DRN and patterns of biomass allocation were investigated in 11 clones of the caespitose, corm-forming, perennial grass Phleum pratense in relation to competitive stress imparted by Lolium perenne in a 16 week glasshouse experiment. A separate experiment assessed the ability of basal buds flanking a corm to sprout and the relationship of corm mass to sprout mass for the same clones. Corm fresh mass varied among clones and was significantly correlated with the dry mass of the tillers that sprouted from basal buds. In the competition experiment, clones in competitive environments varied significantly from those in non-competetive environments in terms of their DRNs for number of tillers and shoot dry mass. Thus, selection of DRNs would favour different genotypes in the two environments and at different times. Significant negative genetic correlations were detected for tiller number and mean tiller mass in the noncompetitive, but not the competitive, environment. Biomass allocation to stem bases was significantly greater for clones under competitive stress. Allocation to storage tissues such as corms may be adaptive if it enhances persistence in the competitive field environments typically occupied by caespitose grasses. Root and shoot allocation showed a significant clone by competition interaction. For P. pratense, genotypic variation in growth trajectories plays an important role in determining variation in individual performance, a condition necessary for the continued evolution of the DRN.