F.A. Lints

Influence of preimaginal environment on fecundity and ageing in Drosophila melanogaster hybrids—III. Developmental speed and life-span

Abstract Mean daily egg-production, total fecundity and imaginal life-span of Drosophila melanogaster hybrids, grown in various preimaginal environments, viz. six temperatures and eight population densities, were measured at 25°C. Duration of development and size at emergence were also recorded. Duration of development and size of hybrids grown at various temperatures are positively correlated. The correlation between those traits is negative for hybrids grown at various population densities. Very different in magnitude and even opposed, the variations of both those traits depend however on each other; this is testified by the identical behaviours of the variations in developmental speed as a function of both preimaginal temperature and population density. Developmental speed is defined as the ratio of the cube of size on duration of development. Total fecundity essentially depends on genotype, and only at extreme values upon the preimaginal environment. Mean daily egg-production, on the contrary, depends on size at emergence, whatever the conditions responsible for that size. Imaginal life-span, which, for a given genotype and in a given imaginal environment, may pass from the simple to more than the double, stricly depends on the developmental speed. Two hypotheses are put forward to explain those data. The first appeals to Medvedevs delayed maturity hypothesis of ageing and the second one links developmental speed to mitotic division rate.

Does the Female Life-span Exceed That of the Male - a Study in Drosophila-melanogaster

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.

An attempt to select for increased longevity in Drosophila melanogaster.

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.

The Lansing effect revisited—I. Life-span

In Drosophila melanogaster, a wild strain has been reproduced at both a young and an old age for ten generations. In each system of reproduction three replicates were made; the experiment was repeated twice. In both experiments the mean longevity of the successive generations drops regularly—although the rates are different according to the reproductive system—to around 40 per cent of the wild strain longevity, increases afterwards up to the original value and then remains probably stable. Our results parallel those of Lansing on three main points. Firstly: the age of the parents at reproduction affects the mean longevity of the offspring. Secondly: that effect is cumulative. Thirdly: that effect is due to neither genic nor environmental factors. Ours and Lansings results differ in three fundamental aspects. Firstly: constant reproduction at both a young and an old age decreases the mean longevity of the offspring. Secondly: as in Lansings experiments the effects are cumulative; the cumulation however does not culminate in the extinction of the lines but only goes up to a certain point where the evolutive trend of the life-span is reversed. Thirdly: that reversibility is not induced by a change in the age at which reproduction occurs but by a feed-back mechanism present in the strain itself. A mathematical model was elaborated which expresses the mean longevity of a given generation in function of general parameters—the parental and grand-parental mean longevities and the relative age at reproduction of the parental generation—and of parameters particular to the strains—optimal and minimal mean longevities. An explanation of the Lansing effects is given in terms of the effects in time and space of the cellular composition and configuration of a given generation on the following generations.

Influence of preimaginal environment on fecundity and ageing in Drosophila melanogaster hybrids I. Preimaginal population density

Abstract 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.

Life Span in Drosophila

Recent experimental evidence does not coincide with the predictions of the different theories of ageing in Drosophila . A review of the evidence and more specifically of the experime

Respiration in Drosophila. II. Respiration in relation to age by wild, inbred and hybrid Drosophila melanogaster imagos.

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. The mean respiration rates and the regressions of respiration rate with age (constant and regression coefficient) differ considerably in the wild, inbred and hybrid populations studied. The “efficiency” of a wild population appears to be higher than both the ones of inbred or hybrid populations, the hybrid “efficiency” being the lowest. When the data relating to the three populations studied are pooled together there exist no relation between the mean respiration rate and the other quantitative traits measured and particularly between the decreases in respiration rate and fecundity with age.

Unexplained variations in life span of the Oregon-R strain of Drosophila melanogaster over a four-year period

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.

Spontaneous locomotor activity and life span: a test of the rate of living theory in Drosophila melanogaster

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 Pearls [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 Longitudinal Study of the Effects of Age on Spontaneous Locomotor Activity in Drosophila melanogaster

The spontaneous locomotor activity of Drosophila melanogaster was observed longitudinally, in both sexes, at young and old age, during a photophase of 12 h. 75 observations of each fly (n = 200 at young age, n = 98 at old age) were made during each photophase. At a populational level and with increasing age the difference between the maximal and minimal percentages of flies active during the photophase diminishes seriously; moreover, the scattering of the observations increases with increasing age. At an individual level females are more active than males at both ages and the scores of activity of both males and females decrease with increasing age. The effects observed, both at the populational and at the individual level, are due solely to age; they are not due to a differential survival depending on or linked to the score of activity exhibited at young age.