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Correlation between life expectancy, flightlessness and actomyosin adenosine triphosphatase activity in the housefly, Musca domestica
183
Arch. Gerontol. Geriatr., 5 (1986) 183-188
Elsevier AGG 00148
Correlation between life expectancy, flightlessness and actomyosin adenosine triphosphatase activity in the housefly, Musca domestica P.L.
Toy and R.S. Sohal
*
Department of Biology, Southern Methodist University, Dallas, TX 752 75, USA
(Received 23 April 1986; accepted 20 June 1986)
Summary The objective of this investigation was to determine if actomyosin ATPase activity in flight muscles is correlated with life expectancy of houseflies. All houseflies lose flying ability before death which permits the identification of shorter-lived flightless 'crawlers' from their longer-lived cohorts, the 'fliers'. Life expectancy of crawlers is about one-third shorter than that of the fliers. Flying performance of houseflies, as measured by the total duration of flying activity during 1 h periods, average duration of flights and the number of rest stops, was highest at 4 days of age and declined thereafter. Actomyosin ATPase activity was higher in the fliers than in the crawlers of the same age. Abolition of flight, by surgical removal of wings at 1 day of age, had no effect on the enzyme activity. Results are interpreted to suggest that actomyosin ATPase activity is correlated with physiological rather than chronological age of flies. life expectancy; aging; actomyosin ATPase; housefly; insect aging Introduction O n e of the most obvious a n d u b i q u i t o u s m a n i f e s t a t i o n s of senescence in a n i m a l s of virtually all p h y l o g e n e t i c groups is the decline in l o c o m o t o r ability. In insects, the flight p e r f o r m a n c e , as i n d i c a t e d b y the total length of c o n t i n u o u s flight, total d i s t a n c e flown a n d the speed of flying have been shown to decrease in old o r g a n i s m s (for review, see Sohal, 1976, 1985). F o r example, in the housefly, which is a very active flyer, flight a b i l i t y declines g r a d u a l l y with age ( R o c k s t e i n a n d B h a t n a gar, 1966) until total flightlessness occurs p r i o r to d e a t h ( R a g l a n d a n d Sohal, 1973). Thus, flight ability, or lack of it, can b e used as an i n d i c a t o r of overall ' vitality' and, m o r e significantly, of i m p e n d i n g d e a t h of the housefly. In an aging p o p u l a t i o n , flies with a shorter life e x p e c t a n c y t h a n their cohorts can be identified on the basis of loss of flying a b i l i t y (Sohal a n d Buchan, 1981). In o t h e r words, flightlessness can be used to i d e n t i f y the short- a n d long-lived subsets of a c o h o r t p o p u l a t i o n .
* To whom correspondence should be addressed, 0167-4943/86/$03.50 © 1986 Elsevier Science Publishers B.V. (Biomedical Division)
184 Activity of actomyosin adenosine triphosphatase (ATPase) has been shown to decrease with age in insects as well as in mammals (Rockstein and Chesky, 1973; Chesky, 1974, 1975, 1978). Actomyosin is considered to play a vital role in muscular activity because it not only comprises the contractile element of the muscle but also contains the calcium-activated ATPase enzyme which hydrolyzes ATP during contraction. Indeed, actomyosin ATPase activity has been reported to correspond to the flight performance of the housefly; enzymatic activity was found to peak shortly after emergence of adult flies and to decline gradually thereafter (Rockstein and Chesky, 1973). In this paper, we report that the age-related decline in actomyosin ATPase activity in the flight muscles of the housefly is associated with aging-related flight failure and life expectancy. ATPase activity may be an indicator of physiological rate of aging.
Materials and Methods
Rearing of houseflies Eggs obtained from 8-10-days-old flies (Cambridge University strain) were placed on moist CSMA medium (Chemical Specialities Manufacturers' Association), obtained from Ralston Purina Co., Richmond, IN, USA. After emergence, flies were fed on a mixture of sucrose, dried milk and egg powder (6 : 6 : 1 ratio by volume, respectively) and water. Throughout life, the ambient temperature was maintained at 25°C and relative humidity at 45%. To study the effects of flightlessness, wings of some flies were surgically removed within the first day after emergence from pupae.
Comparison of flight performance Flight performance of flies was measured at different ages by the procedure outlined by Rockstein and Bhatnagar (1966). An inverted J-shaped thin copper wire was attached to the dorsal mid-thoracic region of the fly using Super Glue ®. The hook end of the wire was inserted in a slender hole drilled in a metal bar supported by two end blocks. A certain percentage of flies thus suspended undertake flight without any stimulus from the experimentalist.
Measurement of actomyosin A TPase activity Actomyosin ATPase activity was measured by the procedure developed by Rockstein and Chesky (1973) for the housefly. In each experiment, a 10% homogenate of thoraces from 25 flies was prepared in cold in a solution consisting of 0.6 M KC1, 0.03 M NaHCO 3 and 0.03 M Na2CO 3. The homogenate was stirred in a cold room for 2 h, and centrifuged at 2000 × g for 15 min at 0-4°C. The supernatant was filtered through surgical gauze under suction to remove exoskeletal fragments and diluted 8-fold by 0.02 M Tris-histidine buffer, pH 6.5, stored
185 overnight in cold to allow full precipitation, and centrifuged at 18000 × g for 20 min at 20°C. The pellet was resuspended in 4 ml of borate buffer, p H 8.5. An aliquot of 0.2 ml of this actomyosin solution was first incubated for 2 - 3 min at 37°C with 1.8 ml of a solution consisting of 1.5 m M MgC12 dissolved in 0.1 m M sodium barbitol, p H 8.8, followed by the addition of 0.1 ml of 30 m M ATP-glutathione solution. After 1 min, A T P hydrolysis was stopped by the addition of 1 ml of cold 20% trichloroacetic acid. The mixture was filtered through W h a t m a n 42 filter paper and the solution was analyzed for inorganic PO 4, liberated from ATP hydrolysis, by the method of Rockstein and Herron (1951).
Resets
Life spans of flies Mortality patterns of aging houseflies have been reported previously from this laboratory (Ragland and Sohal, 1973; Sohal and Buchan, 1981; Sohal et al., in press) and will be mentioned here briefly simply to clarify the reported results. Crawlers isolated from 14-days-old populations had a subsequent life expectancy of 7.7 +__4.2 days, whereas, their flying cohorts had a subsequent life expectancy of 18.0 + 4.2 days. Thus, the average life span of crawlers was 21.7 days and of fliers 32.0 days.
Effect of age on flight performance As shown in Table I, there are several indications that the flight performance of adult houseflies undergoes decline with age. When measured during 'fixed' flight, the total duration of flying during a one-hr period was found to be relatively low in
TABLE I Comparison of flight performance of male houseflies of different ages a Age (days)
n
% Flies undertaking flight b
Av. total flight durationc (rain)
Av. length of flight d (min)
Av. number of rest periods e
2 4 7 14 21
58 50 "59 52 62
65 88 77 51 71
18.7±3.8 36.8±3.6 31.2±4.0 32.9±5.1 18.9±3.0
9.3~2.0 16.5~2.2 12.6~2.0 7.7!1.3 5.7~0.8
2.3±0.3 1.9±0.3 2.2±0.4 3.8±0.7 3.5±0.4
Values are ± SEM. b Experimental flies that began to fly when suspended in the air, hence flight performance data concerns only these flies. c Total time spent in flying during a 60 rain observation period. d Length of individual flights. e Rest periods between successive flights. a
186 the 2-days-old flies, but doubled at 4 days of age and remained relatively high until 14 days of age, followed by a considerable decline by 21-days old flies. Similarly, the average length of continuous flight was highest at 4 days of age, but gradually declined thereafter. The average number of rest periods between flights decreased from 2 to 4 days of age, but steadily increased afterwards. Taken together, results indicate that the flight performance of houseflies, as measured by stamina, was highest at 4 days of age and declined thereafter.
Actomyosin A TPase activity A comparison of actomyosin ATPase activity in the flight muscle of the houseflies, presented in Table II, indicated that at 20 days of age crawlers had a lower level of enzyme activity as compared to the fliers. The lower level of enzyme activity in crawlers does not seem to be due to lack of engagement in flying activity or disuse of flight muscles, since flies whose wings had been surgically removed at 1 day of age exhibited no significant differences in enzyme activity from those that had intact wings. However, experimentally de-winged flies had higher level of enzyme activity than the crawlers; the latter had lost flying ability due to aging.
Discussion Results of this study clearly indicate that the flight performance of houseflies declines with age. Rockstein and Bhatnagar (1966) reported that the duration of flight until exhaustion decreases steadily from 1 to 9 days of age from 420 min to 63 min. Although it is unclear in their paper whether all flies fly under experimental conditions, in this study 12-49% of the flies in different groups did not engage in flight activity under the conditions employed (see Table II). Except for the 21-daysold flies, the ratio of flies undertaking flight corresponded to their flight performance, i.e., both the percentage of flies willing to fly and the duration of flight was highest in 4-days-old flies.
TABLE II Actomyosin ATPase activity in 21-day old flies of different groups a,b,c Group
Actomyosin ATPase activity (nmol PO4/min/mg protein)
Fliers Crawlers b Experimentallyde-winged c
54.9_+1.9 44.5 _+1.7 51.2 _+2.2
a
Values are _+SD. a Fliers are those flies which were able to fly at 21 days of age, b Crawlers are flies that had lost their ability to fly but belonged to the same cohort as the fliers. c Wings of these flies were experimentallyremoved at 1 day of age.
187 Previous studies by Rockstein' group have shown that actomyosin ATPase activity of flight muscles of the housefly decreases with age (Rockstein and Cheskey, 1973). The present study indicates that the enzyme activity is relatively lower in flies with shorter life expectancy. Although the age-related pattern of enzyme activity could not, necessarily, be compared between crawlers and fliers because of the virtual absence of flightless flies in the first half of life, it is reasonable to suggest that actomyosin ATPase activity is related to physiological rather than chronological age of flies. The fact that enzyme activity is independent of flight activity further supports the view that the age-related decline in actomyosin ATPase activity is an expression of intrinsic senescent processes. In the light of the fact that the locomotor function as well as actomyosin ATPase activity also declines with age in mammals (Chesky, 1978), it may be worthwhile to explore further whether this enzyme can be used as a marker of physiological age. Results of this study are consistent with our previous finding which suggests that the loss of flight ability can be used as an indicator of physiological aging in the housefly. It was previously found that the concentration of Schiff-base-like soluble fluorescent material (presumably derived from lipofuscin), which is known to increase with chronological age, is higher in crawlers than in fliers of the same age (Sohal and Buchan, 1981). It has also been previously shown in the housefly that the antioxidant defenses decline, whereas oxygen-free radical by-products increase during the later half of life (Sohal et al., 1984; Sohal and Allen, 1985). Levels of antioxidant defenses, such as superoxide dismutase and catalase activity and glutathione concentration, are lower in crawlers than in fliers. On the other hand, the concentration of the products of free radical reactions, e.g., inorganic peroxides and thiobarbituric acid-reactants, is higher in crawlers than in fliers. Together, the shorter life expectancy and the greater severity of age-related changes in crawlers, suggest that the present model, i.e., comparison of crawlers and fliers, can be used to distinguish age-related changes that are specifically associated with life expectancy or physiological age rather than with chronological age alone. Future studies on the genesis of aging-specific changes and on the genetic or environmental factors which affect them, can potentially lead to the elucidation of the underlying causal mechanisms that bring about the manifested age-related changes in organisms at various levels of biological organization.
Acknowledgement This research was supported by grants from the Glenn Foundation for Medical Research.
References Chesky, J.A. (1974): The intrinsic nature of the loss of actomyosinATPase activityduring senescencein the male housefly, Musca domestica L. Mech. Ageing Dev., 39, 241-244.
188 Chesky, J.A. (1975): Actomyosin ATPase-sensitivity of aging male housefly, Musca domestica L. Exp. Gerontol., 10, 165-169. Chesky, J.A. (1978): In: Aging in Muscle. Editors: G. Kaldor and W.J. Di Battista. Raven Press, New York, pp. 179-210. Ragland, S.S. and Sohal, R.S. (1973): Mating behavior, physical activity and aging in the housefly, Musca domestica. Exp. Gerontol., 8, 135-145. Rockstein, M. and Herron, P.W. (1951): Colorimetric determination of inorganic phosphate in microgram quantities. Analyt. Chem., 23, 1500-1501. Rockstein, M. and Bhatnagar, P. (1966): Duration and frequency of wing beat in the aging housefly, Musca domestica L. Biol. Bull., 131,479-486. Rockstein, M. and Chesky, J.A. (1973): Age related changes in natural actomyosin of the male house fly. J. Gerontol., 28, 455-459. Sohal, R.S. (1976): Aging changes in insect flight muscle. Gerontology, 22, 317-333. Sohal, R.S. (1985): Aging in insects. In: Comprehensive Insect Physiology, Biochemistry and Pharmacology, Vol. 10, Editors: G.A. Kerkut and L.I. Gilbert. Pergamon Press, Oxford. pp. 595-631. Sohal, R.S. and Allen, R.G. (1984): Relationship between metabolic rate, free radicals, differentiation and aging: a unified theory. In: Molecular Biology of Aging. Editors: A.D. Woodhead, A.D. Blackett and A. Hollaender. Plenum, New York, pp. 75-104. Sohal, R.S. and Buchan, P.B. (1981): Relationship between fluorescent age pigment, physiological age and physical activity in the housefly, Musca domestica. Mech. Ageing Dev., 15, 243-249. Sohal, R.S., Farmer, K.J., Allen, R.G. and Cohen, N.R. (1984): Effect of age on oxygen consumption, superoxide dismutase, catalase, glutathione, inorganic peroxides and chloroform soluble antioxidants in the adult male housefly, Musca domestica. Mech. Ageing Dev., 24, 185-195. Sohal, R.S., Toy, P.L. and Allen, R.G.: Relationship between life expectancy, endogenous antioxidants and products of oxygen free radical reactions in the housefly, Musca domestica. Mech. Ageing Dev., in press.
Arch. Gerontol. Geriatr., 5 (1986) 183-188
Elsevier AGG 00148
Correlation between life expectancy, flightlessness and actomyosin adenosine triphosphatase activity in the housefly, Musca domestica P.L.
Toy and R.S. Sohal
*
Department of Biology, Southern Methodist University, Dallas, TX 752 75, USA
(Received 23 April 1986; accepted 20 June 1986)
Summary The objective of this investigation was to determine if actomyosin ATPase activity in flight muscles is correlated with life expectancy of houseflies. All houseflies lose flying ability before death which permits the identification of shorter-lived flightless 'crawlers' from their longer-lived cohorts, the 'fliers'. Life expectancy of crawlers is about one-third shorter than that of the fliers. Flying performance of houseflies, as measured by the total duration of flying activity during 1 h periods, average duration of flights and the number of rest stops, was highest at 4 days of age and declined thereafter. Actomyosin ATPase activity was higher in the fliers than in the crawlers of the same age. Abolition of flight, by surgical removal of wings at 1 day of age, had no effect on the enzyme activity. Results are interpreted to suggest that actomyosin ATPase activity is correlated with physiological rather than chronological age of flies. life expectancy; aging; actomyosin ATPase; housefly; insect aging Introduction O n e of the most obvious a n d u b i q u i t o u s m a n i f e s t a t i o n s of senescence in a n i m a l s of virtually all p h y l o g e n e t i c groups is the decline in l o c o m o t o r ability. In insects, the flight p e r f o r m a n c e , as i n d i c a t e d b y the total length of c o n t i n u o u s flight, total d i s t a n c e flown a n d the speed of flying have been shown to decrease in old o r g a n i s m s (for review, see Sohal, 1976, 1985). F o r example, in the housefly, which is a very active flyer, flight a b i l i t y declines g r a d u a l l y with age ( R o c k s t e i n a n d B h a t n a gar, 1966) until total flightlessness occurs p r i o r to d e a t h ( R a g l a n d a n d Sohal, 1973). Thus, flight ability, or lack of it, can b e used as an i n d i c a t o r of overall ' vitality' and, m o r e significantly, of i m p e n d i n g d e a t h of the housefly. In an aging p o p u l a t i o n , flies with a shorter life e x p e c t a n c y t h a n their cohorts can be identified on the basis of loss of flying a b i l i t y (Sohal a n d Buchan, 1981). In o t h e r words, flightlessness can be used to i d e n t i f y the short- a n d long-lived subsets of a c o h o r t p o p u l a t i o n .
* To whom correspondence should be addressed, 0167-4943/86/$03.50 © 1986 Elsevier Science Publishers B.V. (Biomedical Division)
184 Activity of actomyosin adenosine triphosphatase (ATPase) has been shown to decrease with age in insects as well as in mammals (Rockstein and Chesky, 1973; Chesky, 1974, 1975, 1978). Actomyosin is considered to play a vital role in muscular activity because it not only comprises the contractile element of the muscle but also contains the calcium-activated ATPase enzyme which hydrolyzes ATP during contraction. Indeed, actomyosin ATPase activity has been reported to correspond to the flight performance of the housefly; enzymatic activity was found to peak shortly after emergence of adult flies and to decline gradually thereafter (Rockstein and Chesky, 1973). In this paper, we report that the age-related decline in actomyosin ATPase activity in the flight muscles of the housefly is associated with aging-related flight failure and life expectancy. ATPase activity may be an indicator of physiological rate of aging.
Materials and Methods
Rearing of houseflies Eggs obtained from 8-10-days-old flies (Cambridge University strain) were placed on moist CSMA medium (Chemical Specialities Manufacturers' Association), obtained from Ralston Purina Co., Richmond, IN, USA. After emergence, flies were fed on a mixture of sucrose, dried milk and egg powder (6 : 6 : 1 ratio by volume, respectively) and water. Throughout life, the ambient temperature was maintained at 25°C and relative humidity at 45%. To study the effects of flightlessness, wings of some flies were surgically removed within the first day after emergence from pupae.
Comparison of flight performance Flight performance of flies was measured at different ages by the procedure outlined by Rockstein and Bhatnagar (1966). An inverted J-shaped thin copper wire was attached to the dorsal mid-thoracic region of the fly using Super Glue ®. The hook end of the wire was inserted in a slender hole drilled in a metal bar supported by two end blocks. A certain percentage of flies thus suspended undertake flight without any stimulus from the experimentalist.
Measurement of actomyosin A TPase activity Actomyosin ATPase activity was measured by the procedure developed by Rockstein and Chesky (1973) for the housefly. In each experiment, a 10% homogenate of thoraces from 25 flies was prepared in cold in a solution consisting of 0.6 M KC1, 0.03 M NaHCO 3 and 0.03 M Na2CO 3. The homogenate was stirred in a cold room for 2 h, and centrifuged at 2000 × g for 15 min at 0-4°C. The supernatant was filtered through surgical gauze under suction to remove exoskeletal fragments and diluted 8-fold by 0.02 M Tris-histidine buffer, pH 6.5, stored
185 overnight in cold to allow full precipitation, and centrifuged at 18000 × g for 20 min at 20°C. The pellet was resuspended in 4 ml of borate buffer, p H 8.5. An aliquot of 0.2 ml of this actomyosin solution was first incubated for 2 - 3 min at 37°C with 1.8 ml of a solution consisting of 1.5 m M MgC12 dissolved in 0.1 m M sodium barbitol, p H 8.8, followed by the addition of 0.1 ml of 30 m M ATP-glutathione solution. After 1 min, A T P hydrolysis was stopped by the addition of 1 ml of cold 20% trichloroacetic acid. The mixture was filtered through W h a t m a n 42 filter paper and the solution was analyzed for inorganic PO 4, liberated from ATP hydrolysis, by the method of Rockstein and Herron (1951).
Resets
Life spans of flies Mortality patterns of aging houseflies have been reported previously from this laboratory (Ragland and Sohal, 1973; Sohal and Buchan, 1981; Sohal et al., in press) and will be mentioned here briefly simply to clarify the reported results. Crawlers isolated from 14-days-old populations had a subsequent life expectancy of 7.7 +__4.2 days, whereas, their flying cohorts had a subsequent life expectancy of 18.0 + 4.2 days. Thus, the average life span of crawlers was 21.7 days and of fliers 32.0 days.
Effect of age on flight performance As shown in Table I, there are several indications that the flight performance of adult houseflies undergoes decline with age. When measured during 'fixed' flight, the total duration of flying during a one-hr period was found to be relatively low in
TABLE I Comparison of flight performance of male houseflies of different ages a Age (days)
n
% Flies undertaking flight b
Av. total flight durationc (rain)
Av. length of flight d (min)
Av. number of rest periods e
2 4 7 14 21
58 50 "59 52 62
65 88 77 51 71
18.7±3.8 36.8±3.6 31.2±4.0 32.9±5.1 18.9±3.0
9.3~2.0 16.5~2.2 12.6~2.0 7.7!1.3 5.7~0.8
2.3±0.3 1.9±0.3 2.2±0.4 3.8±0.7 3.5±0.4
Values are ± SEM. b Experimental flies that began to fly when suspended in the air, hence flight performance data concerns only these flies. c Total time spent in flying during a 60 rain observation period. d Length of individual flights. e Rest periods between successive flights. a
186 the 2-days-old flies, but doubled at 4 days of age and remained relatively high until 14 days of age, followed by a considerable decline by 21-days old flies. Similarly, the average length of continuous flight was highest at 4 days of age, but gradually declined thereafter. The average number of rest periods between flights decreased from 2 to 4 days of age, but steadily increased afterwards. Taken together, results indicate that the flight performance of houseflies, as measured by stamina, was highest at 4 days of age and declined thereafter.
Actomyosin A TPase activity A comparison of actomyosin ATPase activity in the flight muscle of the houseflies, presented in Table II, indicated that at 20 days of age crawlers had a lower level of enzyme activity as compared to the fliers. The lower level of enzyme activity in crawlers does not seem to be due to lack of engagement in flying activity or disuse of flight muscles, since flies whose wings had been surgically removed at 1 day of age exhibited no significant differences in enzyme activity from those that had intact wings. However, experimentally de-winged flies had higher level of enzyme activity than the crawlers; the latter had lost flying ability due to aging.
Discussion Results of this study clearly indicate that the flight performance of houseflies declines with age. Rockstein and Bhatnagar (1966) reported that the duration of flight until exhaustion decreases steadily from 1 to 9 days of age from 420 min to 63 min. Although it is unclear in their paper whether all flies fly under experimental conditions, in this study 12-49% of the flies in different groups did not engage in flight activity under the conditions employed (see Table II). Except for the 21-daysold flies, the ratio of flies undertaking flight corresponded to their flight performance, i.e., both the percentage of flies willing to fly and the duration of flight was highest in 4-days-old flies.
TABLE II Actomyosin ATPase activity in 21-day old flies of different groups a,b,c Group
Actomyosin ATPase activity (nmol PO4/min/mg protein)
Fliers Crawlers b Experimentallyde-winged c
54.9_+1.9 44.5 _+1.7 51.2 _+2.2
a
Values are _+SD. a Fliers are those flies which were able to fly at 21 days of age, b Crawlers are flies that had lost their ability to fly but belonged to the same cohort as the fliers. c Wings of these flies were experimentallyremoved at 1 day of age.
187 Previous studies by Rockstein' group have shown that actomyosin ATPase activity of flight muscles of the housefly decreases with age (Rockstein and Cheskey, 1973). The present study indicates that the enzyme activity is relatively lower in flies with shorter life expectancy. Although the age-related pattern of enzyme activity could not, necessarily, be compared between crawlers and fliers because of the virtual absence of flightless flies in the first half of life, it is reasonable to suggest that actomyosin ATPase activity is related to physiological rather than chronological age of flies. The fact that enzyme activity is independent of flight activity further supports the view that the age-related decline in actomyosin ATPase activity is an expression of intrinsic senescent processes. In the light of the fact that the locomotor function as well as actomyosin ATPase activity also declines with age in mammals (Chesky, 1978), it may be worthwhile to explore further whether this enzyme can be used as a marker of physiological age. Results of this study are consistent with our previous finding which suggests that the loss of flight ability can be used as an indicator of physiological aging in the housefly. It was previously found that the concentration of Schiff-base-like soluble fluorescent material (presumably derived from lipofuscin), which is known to increase with chronological age, is higher in crawlers than in fliers of the same age (Sohal and Buchan, 1981). It has also been previously shown in the housefly that the antioxidant defenses decline, whereas oxygen-free radical by-products increase during the later half of life (Sohal et al., 1984; Sohal and Allen, 1985). Levels of antioxidant defenses, such as superoxide dismutase and catalase activity and glutathione concentration, are lower in crawlers than in fliers. On the other hand, the concentration of the products of free radical reactions, e.g., inorganic peroxides and thiobarbituric acid-reactants, is higher in crawlers than in fliers. Together, the shorter life expectancy and the greater severity of age-related changes in crawlers, suggest that the present model, i.e., comparison of crawlers and fliers, can be used to distinguish age-related changes that are specifically associated with life expectancy or physiological age rather than with chronological age alone. Future studies on the genesis of aging-specific changes and on the genetic or environmental factors which affect them, can potentially lead to the elucidation of the underlying causal mechanisms that bring about the manifested age-related changes in organisms at various levels of biological organization.
Acknowledgement This research was supported by grants from the Glenn Foundation for Medical Research.
References Chesky, J.A. (1974): The intrinsic nature of the loss of actomyosinATPase activityduring senescencein the male housefly, Musca domestica L. Mech. Ageing Dev., 39, 241-244.
188 Chesky, J.A. (1975): Actomyosin ATPase-sensitivity of aging male housefly, Musca domestica L. Exp. Gerontol., 10, 165-169. Chesky, J.A. (1978): In: Aging in Muscle. Editors: G. Kaldor and W.J. Di Battista. Raven Press, New York, pp. 179-210. Ragland, S.S. and Sohal, R.S. (1973): Mating behavior, physical activity and aging in the housefly, Musca domestica. Exp. Gerontol., 8, 135-145. Rockstein, M. and Herron, P.W. (1951): Colorimetric determination of inorganic phosphate in microgram quantities. Analyt. Chem., 23, 1500-1501. Rockstein, M. and Bhatnagar, P. (1966): Duration and frequency of wing beat in the aging housefly, Musca domestica L. Biol. Bull., 131,479-486. Rockstein, M. and Chesky, J.A. (1973): Age related changes in natural actomyosin of the male house fly. J. Gerontol., 28, 455-459. Sohal, R.S. (1976): Aging changes in insect flight muscle. Gerontology, 22, 317-333. Sohal, R.S. (1985): Aging in insects. In: Comprehensive Insect Physiology, Biochemistry and Pharmacology, Vol. 10, Editors: G.A. Kerkut and L.I. Gilbert. Pergamon Press, Oxford. pp. 595-631. Sohal, R.S. and Allen, R.G. (1984): Relationship between metabolic rate, free radicals, differentiation and aging: a unified theory. In: Molecular Biology of Aging. Editors: A.D. Woodhead, A.D. Blackett and A. Hollaender. Plenum, New York, pp. 75-104. Sohal, R.S. and Buchan, P.B. (1981): Relationship between fluorescent age pigment, physiological age and physical activity in the housefly, Musca domestica. Mech. Ageing Dev., 15, 243-249. Sohal, R.S., Farmer, K.J., Allen, R.G. and Cohen, N.R. (1984): Effect of age on oxygen consumption, superoxide dismutase, catalase, glutathione, inorganic peroxides and chloroform soluble antioxidants in the adult male housefly, Musca domestica. Mech. Ageing Dev., 24, 185-195. Sohal, R.S., Toy, P.L. and Allen, R.G.: Relationship between life expectancy, endogenous antioxidants and products of oxygen free radical reactions in the housefly, Musca domestica. Mech. Ageing Dev., in press.