INFLUENCE OF PREIMAGINAL ENVIRONMENT OF FECUNDITY AND AGEING IN DROSOPHILA-MELANOGASTER HYBRIDS .I. PREIMAGINAL POPULATION DENSITY

Reciprocal hybrids of two highly inbred lines of Drosophila melanogaster, Gabarros 4 and Abeele, were cultured at 25°C at preimaginal densities of 3, 7, 15, 30, 60, 120, 240 and 480 eggs per standard culture. As previously shown by different authors, the size of the emerging adults diminishes with increasing density, while the duration of development, as measured by the eclosion time of the adults, is greater. From each series of experiments some female flies were tested for daily egg-production throughout their life. With increasing density the mean total fecundity remains constant up to density 240 (80 times the lowest density used); at density 480 it decreases significantly. With increasing density, however, the mean daily egg-production decreases steadily, the number of days of egg-laying increases, while the maximum number of eggs laid in a 24-hr period decreases sharply. When pre-imaginal density increases, the longevity of the emerging imagos, isolated by pairs, increases as well. This increase in imaginal lifespan is not a simple prolongation of the egg-laying period; indeed at high density the length of the final period without egg-production is larger by a factor of six or seven than at low density. With increasing density, the imaginal age at which the maximal egg-production occurs is considerably delayed. The data are discussed in relation to genetical studies where fecundity is measured as an important character related to fitness, to genetical and physiological studies on ageing, and, more generally, in relation to theories of ageing; it is suggested that the data support the delayed maturity hypothesis of Medvedev. © 1969.