Expression of genetic and environmental variation during ageing : 1. Estimation of variance components for number of adult offspring in Drosophila melanogaster.

To test for different gene activity during ageing, an experiment was set up to determine whether or not genetic variation and genetic correlations between fitness traits at different ages change in a systematic way through time. Additive genetic and environmental variance components as well as genetic correlations between different age periods were calculated for the fitness trait "number of adult offspring" in a population of Drosophila melanogaster. Genetic correlations between age periods were all positive and, hence, did not support the theory postulating that genes with beneficial effects on early fitness have pleiotropic unfavourable effects on late fitness. The environmental variation as well as the additive genetic variance showed a clear increase with age. The increase of environmental variation is probably a result of the individuals' increasing difficulties in coping with environmental stress due to physiological deterioration with age. Increased additive genetic variation may be explained by more and more genes being "turned on" with age. Alternatively, it could be caused by accumulation of deleterious mutations with different effects and may reflect the individuals' capacity of DNA repair.