Evolution of phenotypic variance: Non-mendelian parental influences on phenotypic and genotypic components of life-history traits in a generalist herbivore

Abstract

Non-Mendelian parental effects are a form of phenotypic plasticity that influences offspring development and modifies their phenotype. They could have major evolutionary impact by changing the process of selection and the correspondence between offspring genotypes and phenotypes. To examine the influence of parental effects on life-history traits in the obliquebanded leafroller, Choristoneura rosaceana (Harris), three successive generations were raised in a constant laboratory environment, the first and subsequent generations being produced by field-raised and laboratory-raised parents, respectively. Between-generation variation in phenotypic means, variances and among- and within-family variance components were used to assess the magnitude of the influence of parental effects on allelic expression. The differences between parent-offspring regressions derived using parents from the first and second generations were used to estimate the directionality of the influence of parental effects on the family means of the traits. It appears that parental effects influenced the mean and variance of life-history traits at population and family levels. For development time and within-family diapausing propensity, the families of parents developing in a specific environment (laboratory or field) were apparently affected by a similar parental effect. For larval growth rate and pupal weight, it appears that different parental effects transmitted by field parents influenced the family means. Consequently, parental effects transmitted by field parents did not change the correspondence between the offspring phenotypic and breeding values in the first two traits but modified this relationship in the later traits. Parental effects influenced simultaneously the range of phenotypes produced by a genotype and its mean phenotype. Therefore, they may represent a major developmental mechanism by which organisms adapt to unpredictable and predictable environments. © 1994 The Genetical Society of Great Britain.