PHENOTYPIC PLASTICITY IN CREPIS-TECTORUM (ASTERACEAE) - GENETIC CORRELATIONS ACROSS LIGHT REGIMENS

Inbred F-3 and F-4 families from a cross between two contrasting ecotypes of Crepis tectorum were replicated in two regimes in a glasshouse to determine whether genetic tradeoffs within the reaction norm favour genetic differentiation over phenotypic plasticity in this species. There was no tradeoff in reproductive fitness (flower production) across light regimes but genetic cross-environment correlations approached unity for a wide range of characters subject to divergent selection across habitats, suggesting little genetic variation in plasticity and a limited opportunity for selection to favour broadly adapted genotypes capable of attaining the optimum phenotype in every environment. The presence of genotype-environment interaction without large changes in the ranking of genotypes over light regimes indicates a greater potential for evolutionary change in environmental sensitivity although developmental constraints may limit the ranee of phenotypes that can be expressed in a character. A selection analysis was conducted to determine how the average reaction norm would evolve in this system. Whereas the relationship between each trait and reproductive fitness was environment-specific, there was no change in the direction of selection between light regimes. Given the genetic correlation structure observed, one would expect some of the genetic response in one environment to carry over to the other environment.