Maternal Age and Developmental Variability

Abstract

1. Evidence is presented showing that in Drosophila egg-length variability and sterno-pleural chaeta number asymmetry, which are both measures of developmental stability, usually increase with age parabolically, so that both these characters decrease at first to a minimum between the 5th and 12th days of maternal age, then increase to a maximum, although the initial decrease in variability may not necessarily be significant. 2. Maximum hatchability probably occurs at the time of maximum developmental stability. 3. At the time of maximum developmental stability, growing the flies at the extreme temperature of 30°C. has least effect on sterno-pleural chaeta number asymmetry. At this time, therefore, the organism is best buffered against the stresses of the external environment. 4. It is concluded from these studies, and from studies in the mouse and from the literature, that there is an optimum maternal age when the offspring will, in general, be fittest as measured by maximum developmental stability, viability and reproductive ability. 5. It is argued that these results are of application to man, although factors such as variable parental expenditure in man could complicate the situation.