Abstract
All organisms age, the rate of which can be measured by demographic analysis of mortality rates. The rate of ageing is thermally sensitive in ectothermic invertebrates and we examined the effects of temperature on both demographic rates of ageing and on cellular senescence in the blowfly, Calliphora stygia. The short lifespan of these flies is advantageous for demographic measurements while their large body size permits individual-based biochemical characterisation. Blowflies maintained at temperatures from 12°C to 34°C had a five to six-fold decrease in maximum and average longevity, respectively. Mortality rates were best described by a two-phase Gompertz relation, which revealed the first-phase of ageing to be much more temperature sensitive than the second stage. Flies held at low temperatures had both a slower first-phase rate of ageing and a delayed onset of second-phase ageing, which significantly extended their longevity compared with those at high temperatures. Blowflies that were transferred from 29°C to 15°C had higher first-phase mortality rates than those of flies held at constant 15°C, but their onset of second-phase ageing was deferred beyond that of flies held constantly at this temperature. The accumulation of fluorescent AGE pigment, a measure of cellular oxidative damage, increased steadily over time in all blowflies, irrespective of the temporal pattern of mortality. Pigment accumulated steadily during periods of ‘negligible senescence’, as measured by minimal rate of mortality, and the rate of accumulation was significantly affected by temperature. Thus accumulation of AGE pigment is more representative of chronological age than a reflection of biological age or a cause of mortality.
Highlights
Ageing is a universal process that has been identified in organisms ranging from bacteria, to plants and animals [1]
The earlier observation that low temperature extended the life span of Drosophila, an ectothermic animal [3,4], preceded this first observation of caloric restriction extending longevity by almost two decades and, because of the well known effects of temperature on the metabolic rate of ectotherms, these studies were seminal to the development of the ‘rate of living theory of ageing’ [5]
Ambient temperature had a significant effect on survivorship in adult C. stygia (x2 = 2413, df = 5, P,0.0001)
Summary
Ageing is a universal process that has been identified in organisms ranging from bacteria, to plants and animals [1]. The methods best-suited for distinguishing the causes of ageing from age-related changes, are experimental manipulations that extend longevity through cellular and molecular processes conjectured to cause ageing. The earlier observation that low temperature extended the life span of Drosophila, an ectothermic animal [3,4], preceded this first observation of caloric restriction extending longevity by almost two decades and, because of the well known effects of temperature on the metabolic rate of ectotherms, these studies were seminal to the development of the ‘rate of living theory of ageing’ [5]. The effects of low temperature are relatively little used in ageing research in recent times, most likely a result of this connection between temperature and the disproved ‘rate of living theory’ [6]
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