The life span of samples of the Oregon-R strain of Drosophila melanogaster was observed, every fourth week, during a four-year period. Large variations, most probably non-random, were observed at both 25 and 21 degrees C. The possible causes of these variations have been searched for, yet no definite conclusion can be reached. The implications of these results for Drosaphila quantitative genetic research are stressed.

It has been suggested that senescence could have evolved by selection of genes with beneficial effects early in life and detrimental ones later in life (pleiotropy theory of the evolution of senescence). To test that theory, the egg production of 322 females of the Oregon strain of Drosophila melanogaster was recorded daily throughout their life. At the individual level, no relation could be detected between early components of fitness and longevity. For the time being it appears that there are no unequivocal reasons to accept the pleiotropy theory of the evolution of senescence.

Seven generations of selection for high and low spontaneous locomotor activity were made in the wild-laboratory strain Oregon of Drosophila melanogaster. Great care was taken to select for activity and not for reactivity. In opposition with the non totally unambiguous results obtained by another author, absolutely no response to selection could be obtained. Thus the Oregon strain of Drosophila melanogaster does not appear to possess any additive genetic variance for spontaneous locomotor activity. Yet before taking for granted that that conclusion is applicable to all strains of Drosophila melanogaster an experimental selection should be performed again using a freshly captured wild strain.

Spontaneous locomotor activity (SLA), fecundity, fertility and lifespan were measured in a wild laboratory strain of Drosophila melanogaster in order to ascertain whether there is a genetic correlation between these traits. In females there is no correlation either between SLA and fecundity or between SLA and lifespan. It is concluded that, although a high level of SLA probably constitutes a favorable behavioral component of fitness, this does not mean that more active females have a larger number of offspring and live longer than less active ones.

The spontaneous locomotor activity and life span of approximately 600 individuals of both sexes and of three widely different genotypes of Drosophila melanogaster have been measured. Neither at the individual nor at the populational level could a significant correlation between spontaneous locomotor activity and life span be found. The results are discussed in relation with Pearl's [The rate of living, London University Press, London 1928] rate of living theory. That theory has been tested in relation with environmental temperature, oxygen consumption and activity. It is shown that the theory has received no definite confirmation until now.

A survey of all the papers relating to life span in Drosophila melanogaster published in Experimental Gerontology from its origin in 1964 to 1981 shows that, contrary to a common belief, the mean life span of females exceeds that of males in only approximately 50% of the cases. It is shown that mean life span, as it is measured in most experiments, is a poor estimate of the potential life span of a Drosophila strain. However, the analysis of four extensive studies of Drosophila melanogaster life span strongly suggests that the potential (or maximal) life span is consistently higher for females than it is for males. That analysis also shows that, vis-à-vis the controlled or uncontrolled variations of the environment, the males have a broader norm of reaction or, in other words, a smaller homeostasis than the females. A model, mainly based on these two results, allows us to explain how the mean life span of males is so often higher than that of females.

A survey of all the papers relating to life span in Drosophila melanogaster published in Experimental Gerontology from its origin in 1964 to 1981 shows that, contrary to a common belief, the mean life span of females exceeds that of males in only approximately 50% of the cases. It is shown that mean life span, as it is measured in most experiments, is a poor estimate of the potential life span of a Drosophila strain. However, the analysis of four extensive studies of Drosophila melanogaster life span strongly suggests that the potential (or maximal) life span is consistently higher for females than it is for males. That analysis also shows that, vis-à-vis the controlled or uncontrolled variations of the environment, the males have a broader norm of reaction or, in other words, a smaller homeostasis than the females. A model, mainly based on these two results, allows us to explain how the mean life span of males is so often higher than that of females.

Eight generations of selection towards a higher longevity were made in a wild strain of Drosophila melanogaster. Two control lines were also observed. Absolutely no response to selection was obtained whilst a major increase in longevity occurred between F2 and F4 in the three lines under observation. It is shown that the major increase in longevity is due neither to genetic drift, nor to changes in classical environmental conditions. The absence of response to selection is demonstrated to be due neither to a too low selection differential, nor to the absence of genetic variability in the strain, nor to inaccuracy in the measurements, nor to recurrent reproduction at an old age. The impossibility to select towards a higher longevity and the total absence of relation between parental and offspring longevities demonstrate that the very large phenotypic variability displayed by longevity in wild strains of D. melanogaster does not depend on a precise set of specific genes or polygenes with additive action. The results are briefly discussed in relation with inbreeding depression and heterosis for longevity and with similar results obtained in experiments of selection for duration of development.

Reciprocal hybrids of two highly inbred strains of Drosophila melanogaster, Gabarros 4 and Abeele, were cultured, at a preimaginal population density of 30 eggs per standard vial at the temperatures of 16, 19, 22, 25, 28 and 31°C. Afterwards for every preimaginal temperature considered and for the whole life, the daily egg-production of females of known size and duration of development was counted, at 25°C. Life-span was also recorded.

THERE are two principal groups of theories of ageing—those which hold that random cell damage is chiefly responsible for the events characteristic of ageing, which culminate in death and those which hold that ageing and death are genetically controlled. It is too soon to decide between these points of view and in any case Bullough1 has shown that they are not mutually exclusive. So far experiments to test the random error theories of ageing, involving exposure of organisms to unnaturally large or even small amounts of agents such as X-rays and mutagenic agents (for reviews, see refs. 2 and 3), have been controversial and inconclusive.

La mesure toutes les 3, 6, 12 ou 24 h, sous deux photopériodicités distinctes, de la ponte journalière deDrosophila melanogaster a montré que la ponte présente un cycle journalier bien marqué et que celui-ci peut-être modifié par un changement de la photopériodicité.

Rate of oxygen consumption, daily, mean and total fecundity, fertility and adult life span of Drosophila melanogaster imagos were measured, at 25°C, from emergence up to death. Reciprocal hybrids, from the cross between two highly inbred lines, Gabarros 4 and Abeele, produced at preimaginal densities of 30 and 240 eggs per standard tube of 5·7 cm2 of surface, were used. The respiration measurements were carried out according to the technique of Gregg and Lints; all the measurements were realized on individual females; age, size and weight were taken into account.

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.

Rate of oxygen consumption, fecundity and fertility of Drosophila melanogaster imagos were measured at 25°C from emergence up to the death. The populations studied included a wild type Gabarros, mass reproduced for 10 years under laboratory conditi3ns, an inbred Gabarros line resulting from continuous brother-sister matings to the F115 generation, and hybrids produced by pairing Gabarros inbred F132♀ with Abeele inbred F162♂. The respiration measurements were carried out according to the technique of Gregg and Lints; all the measurements have been realized on individual females; age, size and weight have been taken into account.

Eggs of wild-type, inbred and hybrid strains of Drosophila show some differences related to genotype. These appear, however, to be confined to the first stages of development preceding the first movements of the larvae.

Abeele and Gabarros, two inbred lines originating from natural populations, and among which the size was stable at least up to generation 12 and generation 22 respectively, while the viability was decreasing, have been studied in generation 63 and 73 respectively. Different environments including temperature and egg-density conditions were used. The viability and size were diminished to a different extent in the two lines. Hybrids obtained by crossing the 87th and 82nd generation, respectively, of these two lines show a definite heterosis for size and a viability percentage smaller than the one of the parental inbred lines. No reciprocal differences, except in high density conditions, were observed. A second generation, obtained from the F reciprocals raised in different density environments show a breakdown of heterosis for size and a large increase in viability. Carry-over effects due to the different environments in which the reciprocal hybrids were grown were also observed in the second generation. The interference of cytoplasm for “transmission” of acquired characters seems almost certain. Questions are raised concerning the selection opportunity in inbred lines, the influence of parental inbreeding on the character of the hybrids, the opportuneness of the generalization of the homeostasis idea, and the “transmission of acquired characters”.