Change in genetic architecture resulting from the evolution of insecticide resistance: A theoretical and empirical analysis

Under selection for insecticide resistance, the spread of a major resistance allele that has strong pleiotropic effects on life history characters will affect the genetic architecture of fitness. A model is developed showing that the spread of such an allele induces a change in the mean and in the additive genetic variance (heritability) of the life history characters, and in the genetic covariance (correlation) between these characters. The model was tested using a quantitative genetic study that compared, in a lepidopteran species (Choristoneura rosaceana), the genetic architecture of diapause propensity and larval weight within and among insecticide-free and insecticide-treated populations from the same geographical area. Significant genetic correlations between resistance to the insecticides and the life history traits were found within the populations, suggesting that the resistance allele(s) has pleiotropic effects on the life history characters. As resistance develops from an initial value of zero, the model predicts a positive relationship between the degree of resistance within the populations and, (1) the magnitude of the fitness costs, (2) the heritability of the life history traits, and (3) the absolute value of-the genetic correlations between pairs of life history traits. All these predictions were confirmed. Moreover, the evolution of resistance apparently affected the environmental variance in larval weight. Hence, the novel evolution of insecticide resistance appears to result in major changes in the genetic architecture of fitness, which may limit to some extent the colonization of insecticide-treated habitats.