Quantitative genetics of plant tolerance and resistance against natural enemies of two natural populations of Datura stramonium

Abstract

Plants can respond to damage from natural enemies through resistance and/or tolerance. Evolution of these traits among natural plant populations can be constrained by (1) the absence of genetic variation or (2) because ofthe presence of a trade-off between resistance and tolerance. This last hypothesis remains one of the main assumptions of evolutionary theory of plant-natural enemy interactions. Such a trade-off could represent a constraint for adaptive evolution because high levels of resistance or tolerance could be attained but not both. In this study, we examined the presence of genetic variation in tolerance and resistance, the existence of a negative genetic correlation between tolerance and resistance, and the extent of genetic differentiation in plant defensive strategies between two natural populations of Datura stramonium of Central Mexico. A reciprocal transplant experiment using paternal half-sib families was performed. The results of this experiment showed: (I) the presence of additive genetic variation for tolerance and resistance (h 2 N = 0.41-0.49) in both populations at their native site; (2) genetic differentiation in tolerance and resistance between populations; and (3) an environment-dependent genetic correlation between tolerance and resistance. The results support the hypothesis that a negative genetic correlation between tolerance and resistance can potentially constrain the simultaneous evolution of both traits within populations. Furthermore. genetic differentiation between populations supports the expectation that tolerance and resistance represent redundant alternatives against natural enemies. Thus, G x E interactions may represent an important causal factor promoting geographic variation in the outcome of the interaction between plants and their natural enemies.