Lipofuscin as a record of "rate of living" in an aquatic poikilotherm.

As an integral of oxidative metabolism and physiological age index, lipofuscin accumulation was used to evaluate assumptions underlying previous rejection of the rate of living theory of aging. Lipofuscin in the olfactory lobe cell mass of crayfish, Cherax quadricarinatus, was measured throughout life under a wide range of temperature regimes, using image analysis of fluorescence micrographs of brain sections. The relationship between temperature, chronological age, and rate of living, as indicated by lipofuscin accumulation rate, had a complex nonlinear three-dimensional structure, suggesting a thermal optimum, thermal mid-range metabolic compensation, and age-associated variation. The particular experimental window through which this response surface is viewed will have a profound effect on the outcome of life span experiments such as those previously used to test the rate of living theory. The results of this study further challenge assumptions leading to previous rejection of this theory.