THE GENETIC ECOLOGY OF NESTLING GROWTH IN THE GREAT TIT - ENVIRONMENTAL-INFLUENCES ON THE EXPRESSION OF GENETIC VARIANCES DURING GROWTH

1. Growth of Great Tit nestlings was significantly influenced by envir onmental variation consisting of experimentally altered brood sizes an d natural temporal variation in food availability. 2. Two-day weight g ains differed increasingly with age between early (good conditions) an d late (poor conditions) broods. 3. Environmental conditions also affe cted final weight and tarsus length. 4. Nestling growth was studied by estimating genetic and environmental variance components for body wei ght and tarsus length at different ages. The variance component of nes tling weight due to the common environment during rearing predominated under poor conditions, but disappeared during growth under good condi tions. 5. The amount of genetic variation for weight during growth was higher under good conditions than under poor conditions, whereas the expression of variation based on the common environment was higher und er poor conditions.