Relationship between physical activity and life span in the adult housefly, Musca domestica

The objective of this investigation was to explore the relationship between physical activity and life span in adult houseflies and to determine if the normal variations in the life span observed within a population correspond to the levels of physical activity of the individual flies. The levels of physical activity of male flies were experimentally manipulated by surgical removal of wings by varying the size of the housing containers. Walking and flying activities of the houseflies were measured, simultaneously, by a radar-Doppler device. Life spans were significantly prolonged following dealation and in response to conditions which decreased the level of physical activity. The median and the maximum life span of flies singly confined in small bottles, where they could walk but were unable to fly, was about 2.5 times longer than those housed in cages where flying was possible. The life spans were longer and levels of physical activity were lower in flies kept under conditions of solitary confinement as compared to those living in a group. Levels of physical activity of individual flies did, in general, correspond to the life span of the flies. Results of this study support the view that life span in the housefly is strongly influenced by the rate of metabolic expenditure.     

Effect of temperature and different sex ratios on physical activity and life span in the adult housefly, musca domestica

The objective of this investigation was to further examine the relationship between physical activity and life span in the adult housefly. Levels of physical activity were experimentally varied by alterations in the ambient temperature and sex ratios of the populations. In agreement with previous studies, life span of the flies was significantly longer at 18°C than at 28%C. Female flies lived longer than males. Male flies in a population with a high male to female ratio lived a shorter period than their counterparts without any females. These variations in life span seem to be related to differences in the level of physical activity of the flies. The walking and flying activities of the various groups were measured separately by a radar-Doppler system. Walking activity increases about 15-fold, whereas flying activity increased more than 10 times between 15 and 24.5°C; thereafter there was a slight decline in both up to 28°C.Populations with female flies only exhibited lower levels of physical activity as compared to populations of males only. Populations with a high male to female ratio had the highest levels of walking and flying activities. The life spans of the flies were thus inversely related to the level of physical activity. Results of this study support the concept that the rate of metabolic expenditure has a strong influence on life span. The nature of the underlying mechanisms is, however, as yet obscure.     

Effect of experimentally-prolonged life span on flight performance of houseflies

Reduction of metabolic rate by the elimination of flying activity extends the life span of male houseflies about two-fold as compared to those permitted to engage in flying activity. Flying performance of flies is known to undergo an age-associated decline. The objective of this study was to determine if such an age-related decline in flight performance is delayed by the reduction of metabolic rate. Flight performance was measured, by cross-sectional sampling at different ages, by the “stationary flight” methods, as the total time spent in flight and the number and duration of individual flights and rest stops during a one hour observation period. Flies kept under conditions of low physical activity exhibited a superior flight performance at all ages as compared to those kept under high activity conditions. The decline in flight performance observed in old flies was delayed in the longer-lived low activity flies as compared to the shorter-lived high activity flies. Results support the concept that the rate of aging in houseflies is modified by variations in the level of physical activity.     

Oxygen consumption and life span in the adult male housefly,Musca domestica

The object of this study was to re-examine the quantitative relationship between metabolic rate and life span postulated by the rate of living hypothesis. The metabolic rate of the adult male flies was experimentally altered by varying the level of physical activity and ambient temperature. Lowering of physical activity and ambient temperature increased the life span of the flies. Metabolic rates of flies in all groups declined during older age, however, the relative decrease was greater in the high activity flies as compared to the low activity flies. The total amount of oxygen consumption, till average life span, was nearly equal in the low and high activity flies maintained at the same temperature, but this amount was 12–15% greater in flies maintained at 18°C than at 25°C. The results support the postulates of the rate of living hypothesis. The possible reasons for the differences in the metabolic potentials at different temperatures are discussed.     

Relationship between gamma-irradiation, life span, metabolic rate and accumulation of fluorescent age pigment in the adult male housefly, Musca domestica

The patterns of fluorescent age pigment (FAP) accumulation in response to gamma-irradiation were examined in adult male houseflies under conditions of relatively high and low levels of physical activity. Flies were exposed to 0, 20, 40, and 66 kR and their level of physical activity was altered by permitting or restricting flight activity. Under conditions of high activity the mean life span of flies exposed to 20 kR and 40 kR was greater than in the controls. The mean life span of high activity flies exposed to 66 kR and all groups of low activity irradiated flies was less than the control life span. The force of mortality as indicated by Gompertz slope was greater in high activity controls than in unirradiated flies maintained under low activity conditions. Gompertz slope was similar in corresponding high and low activity groups exposed to radiation. Radiation decreased the rate of FAP accumulation in high activity groups, but increased the rate of FAP accumulation under low activity conditions. The low activity control and low activity flies exposed to 20 kR had a lower FAP accumulation than the corresponding high activity groups at 14 days of age. At this age, low activity groups of flies exposed to 40 kR and 66 kR had concentrations of FAP that were similar to the corresponding high activity groups. These results indicate that radiation exposure decreased longevity by causing damage rather than by increasing the rate of aging.     

Properties of a strain of free-living nematode, Rhabditidae sp.: life cycle and age-related mortality

Some properties, especially the life cycle and the temperature-dependency of age-related mortality, of a newly isolated free-living nematode have been investigated. The nematode was identified as a member of the family Rhabditidae, but the genus has not yet been identified. The nematode is bisexual and the male to female ratio was found to be 1 : 15. In all experiments animals were cultured with Escherichia coli cells as a food source. At 20°C, eggs hatched to larvae after about 24 hours and the eggs of the next generation appeared in a population about 5 days after being laid. The longevity of the nematode was greatly influenced by the temperature. The average life span observed for virgin females at 20°C was about 95 days and that at 35°C was 30 days. The life span of the females which had laid eggs was shorter than that of virgin females. Virgin males were also found to have a shorter average life span than virgin females. One female lays about 100 eggs during its life span. It was shown that one third of 100 days old virgin females could mate with males and produce about 100 eggs per female with almost complete hatchability. These results indicate that this particular nematode is a useful animal for the study of aging, like other free-living nematodes currently being used in aging research.     

Aging can be genetically dissected into component processes using long-lived lines of Caenorhabditis elegans.

The aging process has been dissected by analysis of genetic variants of the nematode Caenorhabditis elegans. Long-lived recombinant inbred lines were generated; some of these lines have mean and maximum life spans up to 70% longer than wild type. Longer life results from a slowing of the characteristic exponential increase in mortality rate that is typical of aging populations in all species. The length of developmental periods and the length of the reproductive period are unrelated to increased life span. Lengthened life is due entirely to an increase in postreproductive life span. Development, reproduction, and life span are each under independent genetic control. General motor activity decays linearly with chronological age in all genotypes. The decay in general motor activity is correlated with and a predictor of life span, suggesting that both share at least one common rate-determining component.     

Effects of experimentally altered life spans on the accumulation of fluorescent age pigment in the housefly, Musca domestica

The effects of experimentally alteredlife spans on the rate of fluorescent age pigment (FAP) accumulation were studied in the adult male houseflies. Two-fold differences in the median and the maximum life spans of the flies were achieved by varying the flight activity. The rate of FAP accumulation was significantly faster in the short-lived high activity flies than in the long-lived low activity flies. The maximum concentration of FAP reached was similar in both groups. The results strongly support the view that FAP accumulation is associated with physiological rather than chronological age of the houseflies. It is suggested that FAP be used as a cellular marker for physiological age.     

Favorable effects of the antioxidants sodium and magnesium thiazolidine carboxylate on the vitality and life span of Drosophila and mice.

We have investigated the effects of two antioxidants, sodium and magnesium L-thiazolidine-4-carboxylate (NaTC, MgTC), on vitality and life span of female mice and male Drosophila melanogaster (fruit flies). NaTC or MgTC was added to the food medium of populations of flies (about 170 flies each) at a 0·2% concentration from the 26th day of their adult life, whereas MgTC was given to 39 mice at the concentration of 0·07% in their standard chow, starting at the age of 23 months. The antioxidant treatment resulted in mean life span increases of 8 and 14% in flies treated with NaTC and MgTC, respectively. Apparently, the maximum life span was similarly increased as reflected in the ages of the longest lived individuals, although much larger populations should be studied for statistical evaluation. It seems that mouse aging was also influenced by antioxidant treatment, although to a lesser degree than Drosophila aging. This is suggested by our observation that mice given MgTC had a median life span about 7% longer than the control animals. Vitality of middle aged flies (assessed by measuring their mating capacity) receiving MgTC was increased considerably in comparison with the controls. The mean body weights of groups of treated flies and mice were not different from those of the controls and the food intake was about the same for control and treated mice. Therefore, the favorable effects of the antioxidants MgTC and NaTC on mortality kinetics of flies and mice and on the vitality of flies cannot be explained as the outcome of caloric restriction. In our opinion, the favorable results which are consistently associated with the use of NaTC, MgTC or other sulphur-containing substances are related to their free radical scavenger action. In accordance with this concept, the above substances may be effective in reducing the rate of the aging process.     

Temperature-dependent trade-offs between longevity and fertility in the Drosophila mutant, methuselah

Single gene, hypomorphic mutations which extend the life spans of cold-blooded animals, such as the methuselah (mth) mutation in the fruit fly, Drosophila melanogaster, may have additional, deleterious effects on overall fitness. The hypotheses tested here were: (i) that the extension of life span by mth might be temperature-dependent, and (ii) that it might be associated with depression of reproductive output, physical activity, or the rate of metabolism. The effect of mth on life span was smaller in magnitude than reported previously, and it was both sex-specific and temperature-dependent. Female longevity was increased only at 29 degrees C, whereas for male flies the extension of mean life span diminished progressively from 15-25% 25-29 degrees C to 2% at 18 degrees C, and the survival time at 4 degrees C was decreased by 22-39%. Conversely, the lifetime reproductive output of mth mutants was decreased at 29 degrees C, but increased at 18-22 degrees C. The walking speed of mth flies was significantly elevated, but mth had no effect on the rate of oxygen consumption at 25 degrees C. Collectively, the results demonstrate that where the life span is extended, there is an offsetting effect on reproductive output, suggesting that mth induces trade-off effects and is not a direct, mechanistic regulator of the aging process.     

Proteomic profiles reveal age-related changes in coelomic fluid of sea urchin species with different life spans

Sea urchins have a different life history from humans and traditional model organisms used to study the process of aging. Sea urchins grow indeterminately, reproduce throughout their life span and some species have been shown to exhibit negligible senescence with no increase in mortality rate at advanced ages. Despite these properties, different species of sea urchins are reported to have very different natural life spans providing a unique model to investigate cellular mechanisms underlying life span determination and negligible senescence. To gain insight into the biological changes that accompany aging in these animals, proteomic profiles were examined in coelomic fluid from young and old sea urchins of three species with different life spans: short-lived Lytechinus variegatus, long-lived Strongylocentrotus franciscanus and Strongylocentrotus purpuratus which has an intermediate life span. The proteomic profiles of cell-free coelomic fluid were complex with many proteins exhibiting different forms and extensive post-translational modifications. Approximately 20% of the protein spots on 2-D gels showed more than two-fold change with age in each of the species. Changes that are consistent with age in all three species may prove to be useful biomarkers for age-determination for these commercially fished marine invertebrates and also may provide clues to mechanisms of negligible senescence. Among the proteins that change with age, the ectodomain of low-density lipoprotein receptor-related protein 4 (LRP4) was significantly increased in the coelomic fluid of all three sea urchin species suggesting that the Wnt signaling pathway should be further investigated for its role in negligible senescence.     

Characterization of a life-extending mutation in age-2, a new aging gene in Caenorhabditis elegans

We have generated a life-extending mutation, yw23, in Caenorhabditis elegans. The mutation is in what appears to be a new aging gene, which we have designated age-2. When homozygous, yw23 produces an increase of mean and maximum life span of about 20% over that of the wild-type strain, N2. Strain HG23 [age-2(yw23)] was obtained by screening for longer life spans among 430 lines of nematodes two generations after exposure to the mutagen ethylmethanesulfonate. Strain HG231 [age-2(yw23)] was obtained after a single out-crossing of HG23 to N2. When compared with N2, HG231 exhibits normal motility, slightly higher swimming rates, reduced fertility (especially at higher temperatures), somewhat longer development times, and a slightly larger size at the time of first egg laying. A Gompertz analysis suggests that HG231 extends life span by reducing the initial mortality rate. In genetic crosses, yw23 complements other known aging mutants in C. elegans genes-age-1, daf-2, spe-26, clk-1, clk-2, clk-3, and gro-1. A double-mutant strain, HG284, combining mutations in age-1 and age-2, lives longer than animals with individual mutations in either age-1 or age-2, and exhibits a longer life span at 25 degrees C than at 20 degrees C.     

Flight activity, mortality rates, and lipoxidative damage in Drosophila

In this study, the effect of flight activity on mortality rates and lipoxidative damage in Drosophila was determined to identify mechanisms through which oxidative damage affects life span. The results showed that flies allowed flying throughout life had higher mortality rates and decreased median and maximum life spans compared to controls. The mortality rate of the flight activity group could be lowered, but not completely reversed by switching to control conditions; and the accrued oxidative damage could not be eliminated. The levels of reactive oxygen species produced by mitochondria isolated from high activity and control flies did not differ significantly. However, the high activity flies had altered membrane fatty acid compositions, which made them prone to increased lipid peroxidation. The effect of flight activity on insect life span differs considerably from the beneficial effects of exercise in mammals; these differences may be caused by physiological differences between the two taxa.     

Life cycle of the nematode Contracaecum rudolphii Hartwig, 1964 (sensu lato) from northern Poland under laboratory conditions

Summary The study was aimed at following, under laboratory conditions, embryogenesis of the nematode Contracaecum rudolphii, and at identifying its intermediate hosts in northeastern Poland. Nematode eggs, isolated from the terminal part of the female uterus, were placed in 0.9 and 3% NaCl solutions, 1% formalin, and in tap water. Each solution batch was divided into 3 parts kept at 4, 15, and 23°C. Regardless of the temperature they were exposed to, the eggs placed in 1% formalin showed numerous deformations; as few as 5% of those eggs produced larvae. Embryogenesis was at its fastest in the eggs kept at 23°C. While still within the eggs, the larvae underwent two moults. The eggs hatched to produce the stage 3 larvae, which emerged surrounded by the cuticle of the preceding larval stage. Experimental infestations of zooplankton collected from Lake Kortowskie showed that only cyclopoid copepods could serve as the intermediate hosts. No differences in the infestation intensity were found between the guppies infested by the invasive larvae and those fed the infested cyclopoids.     

Does an extension of the developmental period in Drosophila cause the prolongation of adult life?

It is accepted by some authors that by stretching the developmental program, by lowering the developmental temperature in a physiological range, adult longevity can be prolonged. In order to test this hypothesis in Drosophila melanogaster two groups of flies were acclimated at 20 and 28°C by self mating for 10 generations. The life tables for both sexes of the two temperature groups of flies were constructed at both temperatures. Flies raised at 28°C had a very similar life span at 28°C in comparison to those raised at 20°C. Again the flies developed at 20°C and tested at 20°C did not live for a shorter period than those raised at 28°C and tested at 20°C. When the life spans of the two temperature groups of flies were measured at 25°C, again no significant differences were observed between the averages of the flies collected from the 20°C and 28°C cultures. It is concluded that the life span of both male and female flies is independent of developmental temperature. The pertinent data on the subject is compared with ours and the subject evaluated.     

Ubiquitous overexpression of CuZn superoxide dismutase does not extend life span in mice

Oxidative damage has been implicated in the aging process and in a number of degenerative diseases. To investigate the role of oxygen radicals in the aging process in mammals, the life spans of transgenic mice on a CD-1 background expressing increased levels of CuZn superoxide dismutase (CuZnSOD), the enzyme that metabolizes superoxide radicals, were determined. Homozygous transgenic mice with a two- to five-fold elevation of CuZnSOD in various tissues showed a slight reduction of life span, whereas hemizygous mice with a 15- to 3-fold increase of CuZnSOD showed no difference in life span from that of the nontransgenic littermate controls. The results suggest that constitutive and ubiquitous overexpression of CuZnSOD alone is not sufficient to extend the life spans of transgenic mice.     

Effects of mating status, sex ratio, and population density on longevity and offspring production of Cryptolestes ferrugineus (stephens) (Coleoptera: Cucujidae)

The life span and reproductive rate of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), were determined at different adult densities and sex ratios at 30 ± 1°C, 75 ± 5% relative humidity (RH), and with feed consisting of ground wheat plus wheat germ (4:1, w/w). The mean life spans of adult beetles were 32 weeks for adults individually isolated in separate vials, 22 to 25 weeks for adults of different strains kept one male and one female per vial, 24 weeks for a group of 30 virgin females together in one vial, 13 weeks for a group of 30 virgin males together in one vial, 14 weeks for groups with 10 males and 20 females per vial, 13 weeks for groups with 15 males and 15 females per vial, and 12 weeks for groups with 20 males and 10 females per vial. When kept one adult per vial, males and females had similar life spans; when kept one male and one female per vial, males lived longer; when kept in groups of 30 per vial females lived longer, except in the group which had a sex ratio of two males to one female; in this group life spans of males and females were the same. Females in separate vials with one male produced mean numbers of offspring ranging from 389 for an inbred homozygous malathion-resistant strain to 514 for an outbred strain (genetically variable: GV). GV train females in vials which had 10 males and 20 females produced a mean of 97 offspring, GV strain females in vials which had 15 males and 15 females produced a mean of 146 offspring, and GV strain females in vials which had 20 males and 10 females produced a mean of 216 offspring.

The results of this study and similar studies on other insect species suggest that the life span of this insect is inversely related to the rate at which it expends energy and to injury incurred during copulation, and that oviposition rate decreases as the density of larvae and female adults increases.     

Long-lived lines of Caenorhabditis elegans can be used to establish predictive biomarkers of aging

Long-lived recombinant inbred lines, some of which have mean and maximum life spans up to 70% longer than wild type, were used in these analyses. Longer life results from a slower exponential rate of increase in mortality. General motor activity decreases with chronological age in all genotypes; this decay in general motor activity is a biomarker of aging in that it is a predictor of maximum life span. The aging process has also been dissected into component processes. The length of development and the length of reproduction are unrelated to increased life span; lengthened life is due entirely to an increase in post-reproductive life span. Development, reproduction, and life span are each under independent genetic control. General motor activity and life span share at least one common rate-determining genetic component.     

Lipofuscin accumulation: effects of individual variation and selective mortality on population averages.

A method for evaluating the effects of individual variation and selective mortality on population life span patterns of age-specific biological parameters is tested using mortality and lipofuscin accumulation data from housefly populations. It is shown that unusual features of the experimental population life span pattern of lipofuscin accumulation in houseflies, namely, a leveling off and possible decrease in population averages at older ages, may be a result of individual variation in the housefly population which leads to selective mortality of houseflies. This result leads to the expectation that many of the unexplained features observed in the population life span patterns of age-specific biological parameters may be due to individual variation which exists in all populations and the resultant selective mortality.     

Effects of caloric restriction are species-specific

This article addresses two questions: (1) ‘can caloric restriction (CR) extend the life spans of all species of experimental animals’, and (2) ‘is CR likely to slow the human aging process and/or extend the human life span?’ The answer to the first question is clearly ‘no’, because CR decreases the life span of the housefly, Musca domestica, and fails to extend the life span of at least one mouse strain. The answer to the second question is unknown, because human CR has not yet been shown either to increase or curtail the human life span. However, recent efforts to develop insect models of CR have been unsuccessful and/or relatively uninformative, so any insights regarding the relationship between CR and human aging are more likely to arise from studies of established, mammalian models of CR.