A crucial assumption of evolutionary theories of aging is that age-specific differences of life history traits may have genetic causes. The present study focuses on the existence of such differences between eight freshly caught populations of Drosophila melanogaster. A highly significant differentiation of the populations is observed, yet it accounts for a relatively small part of the variance. It is also shown that large discrepancies may be found between the estimations of fitness based, on the one hand, on data for egg production and, on the other hand, on fertility data. This stresses the need for accurate measurements of fitness for the assessment of evolutionary theories. Finally, the results suggest that neither of the current evolutionary theories of aging is generally valid. Indeed, the age-specific differences that are found between the populations match either the antagonistic pleiotropy mechanism, or the concordant pleiotropy mechanism, or none of them.

The spontaneous locomotor activity of young, middle-aged and old Drosophila melanogaster of both sexes has been videorecorded during three parabolic flights separated by one-day intervals. Fast shifts between 0 g, 1 g and 1.8 g phases are obtained during parabolic flights. Results showed that the activity scores were higher at 0 g during the first flight, but that this effect of microgravity was erased during the two next flights. It may be concluded that flies showed a transient form of reactivity to a new environment, i.e. to repeated rapid variations of gravity levels.

From the data of an experiment of selection for increased longevity, a realized heritability of longevity was calculated. The low value of this heritability (3.4%) was very close to values observed in other experiments concerning Drosophila melanogaster wild strains. The error variance of the heritability estimator was calculated through the use of orthogonal contrasts. In this way, it was possible to calculate the confidence interval of the realized heritability. The amplitude of this interval was wide although the size of the sample was large. This shows the difficulty of estimating with precision the heritability of longevity from data obtained in selection experiments.

Life history traits--hatchability, longevity, and egg production--of five wild-caught populations of Drosophila melanogaster were measured after these populations had been reared in constant laboratory conditions during a 4-year period. The results were analyzed together with those that had been obtained with the same populations just after capture. They are probably the first convincing results that reveal the existence of genetic variability for some life history traits measured in the laboratory. Besides, no significant phenotypic correlations, either positive or negative, between early and late components of fitness were found. Finally, the five populations showed different patterns of genetic correlation between early and late fitness traits. One of the populations showed a negative correlation, another showed a positive correlation, while the remaining three populations showed no correlation at all. This was equally observed at the within- and between-population levels. That result suggests that both the antagonistic pleiotropy hypothesis proposed by Williams and the concordant pleiotropy hypothesis suggested by Lints are not of general validity.

The life-span of Drosophila melanogaster males kept for their entire life in atmospheres of differing O2 concentration (21%, 30%, 40%) was measured. The life-span decreased linearly with the increase in O2 proportion. In order to test the rate of living and the threshold theories of ageing, Drosophila melanogaster males were kept for 15 days in a given atmosphere and from day 16 on in another one. The life-spans observed in these alternate conditions were very close to the values predicted by the rate of living theory and are thus not compatible with the threshold theory.

Life history traits--hatchability, developmental time, longevity, and egg production--of five freshly caught European populations of Drosophila melanogaster were measured under homogeneous laboratory conditions. No significant phenotypic correlations between early and late fitness could be found for the five populations at the within-population level. At the between-population level, no consistent indication of any significant genetic correlation, either positive or negative, was detected for the same traits. These results are not in agreement either with the predictions of the antagonistic pleiotropy hypothesis proposed by Williams, nor with the opposite hypothesis suggested by Lints. The results suggest that natural populations of Drosophila melanogaster are genetically different for at least some life history traits measured in the laboratory as soon as possible after capture.

Longevity of mated and virgin Drosophila melanogaster flies was observed at various gravity levels (1–7.38 g). A slight longevity decrease was observed in the 1–5.14 g range for virgin males, and a larger one in the 5.14–7.38 g range. The effect of gravity was larger for females in the 1–5.14 g range, and at the highest gravity level, bot hsexes had roughly the same longevity, which however remained high (around 40 days). The longevity of mated flies was lower than that of virgins at 1 g, and only a slight longevity decrease was observed in the 1–7.38 g range in females, this decrease being larger for males. Hypergravity appears to have no dramatic effects on life span and to be of lower importance than the simple effect of mating. This study confirms previous results obtained in the 1–5.02 g range with virgin flies (Le Bourg and Lints, 1989).

The study of the genetic determination of longevity in Drosophila melanogaster has made use of the technique of late-age reproduction. At low larval density, that indirect selection showed no effect. At high larval density, however, increased mean life-span in lines reproduced at late age was observed. When these last data are examined as a function of the number of days after the beginning of the experiment, instead of as a function of generations, the difference in life-span between early and late lines at high larval density disappears. The erratic evolutions of mean longevities in all the experiments here described may be attributed to unexplained variations in life-span previously observed in a 4-year experiment. Considering the time lag between the measurement of a given generation in early and late lines, the experiments of reproduction at late age cannot demonstrate the genetic determinism of longevity.

The paths of young, middle-aged and old Drosophila melanogaster flies, kept at various gravity levels (1-5 g) throughout life, have been recorded in a cross-sectional study. Aging flies exhibit more sinuous paths and do not move as far away from their release point as younger ones. These age-related changes in the patterns of movement are expressed at younger ages in flies submitted to hypergravity. As for the climbing activity experiment, the patterns of movement do not clearly vary with the gravity level at young age. Results are discussed in relation to the hypothesis of increased aging rate in hypergravity.

The spontaneous locomotor activity (SLA) of Drosophila melanogaster flies kept at various gravity levels (1-5 g) was recorded in both longitudinal and cross-sectional experiments. No gravity level effect could be detected in the longitudinal one, probably because these flies were allowed (for technical reasons) to rest at 1 g for 15% of their life. By contrast, flies kept at 5 g in the cross-sectional experiment had lower SLA scores at middle and old age than both 1 and 3 g-kept flies. The results of this series of experiments on hypergravity (HG) effects on three forms of locomotor activity (climbing activity, patterns of movement and SLA) allow to conclude that aging is accelerated in HG, even if no longevity decrease could be detected in the 1-4 g range.

Drosophila melanogaster flies climb up the sides of their vial after having been submitted to a mechanical stimulation; that ability is impaired at older ages. The climbing activity (CLI) of flies kept at various gravity levels (1, 3 and 5 g) has been measured throughout life, in cross-sectional studies. Hypergravity had no effect on CLI at young age, but older flies kept in hypergravity displayed lower scores than flies kept at 1 g. Results are discussed in relation with the hypothesis of increased aging rate in hypergravity.

The proboscis extension response threshold to sucrose has been measured in young, middle-aged and old male Drosophila melanogaster flies living at a gravity level of 1, 3.02 or 5.02 g until the experiment. The threshold increased with age and no effect of gravity level was observed at any age. These data are at variance with those of previously studied behavioral traits which showed that flies living in hypergravity seemed to age faster than 1-g ones.

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.

Free radicals produced during normal metabolism cause damage to macromolecules. The free radical theory of aging proposes that the organism is unable to repair all of them and that, with time, unrepaired damages accumulate and put the organism at risk: in other words, free radicals provoke aging and death. This article reviews both the results of adding antioxidants to food on longevity in Drosophila melanogaster, as well as the studies on antioxidant enzymes (inactivation in vivo, null mutants, overexpression). It is concluded that antioxidant enzymes are probably poorly connected to the normal aging process, but they allow the organism to cope with stressful conditions.

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.

The concept of an inverse relationship between life span of adult Drosophila and their developmental temperature is probably the result of an unwarranted generalization. Rather, in a wild-type laboratory strain the present study revealed a plateau phase in this relationship between 16 and 29 degrees C in which life span of both male and female flies was roughly independent of developmental temperature. Below and above this range, life span dropped drastically, development being impossible below 12 and above 32.5 degrees C. Simultaneous study of growth characteristics showed that the plateau phase corresponded to a 'physiological' range of developmental temperature, development being apparently disturbed outside that range. Within that physiological range, the growth rate of the flies varied varied 2-fold, while life span remained constant corroborating our previous conclusion that growth rate per se does not determine life span.

The patterns of variation of wing cell size and number were studied under developmental conditions leading to a biphasic relationship between life span and growth rate while duration of development remained constant (development on an agar-only medium with a varying added yeast amount, constant temperature (25°C) and constant larval density). Across the yeast range, a 125% increase of body weight was accompanied by a roughly 30% increase in the wing linear dimensions, wing cell size and wing cell number while estimated duration of cell division and its reciprocal mitotic division rate remained constant. Furthermore, cell size (but not cell number) varied with growth rate in a similar biphasic pattern to that observed for life span. Finally, from a simultaneous examination of the covariation patterns of life span, growth rate, cell size and cell number with decreasing yeast amount, it became apparent that there was a “critical“ yeast amount, approximately 125 mg/120 eggs, below which: (a) cell number abruptly started to decrease linearly from a roughly constant value; (b) the rate of the slow decrease of cell size now tripled and that of growth rate increased even more; and (c) life span which, in the upper yeast range, increased slowly with decreasing yeast, apparently reached a maximum at the critical yeast level and decreased three times faster below that level. These data taken together suggest that: (i) the decrease of all parameters (including life span) below the critical yeast results from a presumably suboptimal or disturbed development because of and in proportion to the lack of nutrients and (ii) the increase of life span with decreasing yeast amount above the critical yeast level has not been definitely explained but some possibilities are suggested such as changes in subcellular organelle numbers, size and/or functional properties, or other changes due to a phenomenon equivalent to food restriction in rats, probably without changes in overall metabolic rate of the flies.

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.

Sixty-eight years ago Northrop observed a constant life span in Drosophila after a progressive increase of the duration of development of the flies achieved by using a yeastless nutrient medium to which he added yeast with a progressively increasing delay. This evidence against the more recent concept of an increased life span following an experimentally decreased developmental rate has generally been ignored due, presumably, to the imprecise methodology employed by Northrop at a time that Drosophila research was just commencing. We describe here a study that aimed at re-examining and extending Northrop's work by developing the flies either a yeastless or a lightly yeasted medium. While in a yeastless medium development of flies was virtually arrested until yeast was added, in the yeasted medium a slow growth of the larvae was possible before yeast was added. With another method, larval growth rate was reduced over the entire developmental period by adding a relatively low amount of yeast in four portions and with various delays between portions (the first portion being added without delay). Our study confirmed the “Northrop-effect”, i.e. the absence of an effect on life span from increased duration of development by a virtual arrest of growth of the larvae for a number of days. Further, it showed that manipulation of growth rate by portioning the yeast amount did not unequivocally support the concept that a lower growth rate leads to an increased life span.