Parental effects in Pieris rapae in response to variation in food quality: adaptive plasticity across generations?

Abstract. 1. Herbivores using seasonal resources must cope with variation in the quality of their host plants. The effects of variation in protein concentration of artificial diet and glucosinolate concentration in canola, Brassica napus , on Pieris rapae parental and progeny growth were investigated. 2. The hypothesis that parents respond to variation in food quality by altering the phenotype of their progeny to enhance progeny fitness was tested. Consistent with previous studies, P. rapae was not affected strongly by variation in the protein concentration of artificial diet and had equal mass on completing development. 3. The mass of individual eggs of P. rapae progeny was correlated negatively with the amount of protein in the diet on which parents fed. Moreover, mothers reared in extreme conditions (high and low protein) produced progeny that grew best under those conditions. These potentially adaptive parental effects were detected early in progeny growth but not later in their development. 4. Early larval growth of P. rapae was affected negatively by increasing glucosinolates in B. napus plants, although no effects of glucosinolates were detected later in growth or on the progeny's phenotype. 5. Thus, evidence is presented that variation in food quality (protein concentration) has major consequences for the progeny of P. rapae . Given the multivoltine life history of P. rapae and the seasonal differences in food quality it encounters, such parental effects may be adaptive.