The influence of life-history differences on the evolution of reaction norms

Abstract

We analyse a general model for the evolution of reaction norms in a heterogeneous environment. In the life-cycle, zygotes disperse. Development to the adult phenotype is in one environment and selection in another environment after adult migration. Lack of adult migration always leads to the optimum reaction norm. Adult migration after development and unpredictability of selection are necessary for the evolved reaction norm to deviate from the optimum reaction norm. Zygote dispersal and adult migration, therefore, play very different roles in the evolution of reaction norms. The life-cycle includes three stages in which density-dependent number regulation can take place: in the environment of development and in the environment of selection before and after selection. Differences in productivity between patches - a source-sink structure - cause major deviations in phenotypic evolution. Weak optimizing selection leads to a compromise reaction norm heavily influenced by productivity differences. Strong optimizing selection leads to the phenotypic optima for the character states and might lead to a polymorphic reaction norm; the condition is that density-dependent number regulation is present after selection. Zygote dispersal around the parental patch causes density-dependent number regulation in the environment of development to influence the evolved reaction, as it is now effectively after selection. The influence of density-dependent number regulation, therefore, depends strongly upon the exact life-cycle.