Water balance and cation levels in Drosophila: can early physiological decline predict aging and longevity?

Many studies demonstrate changes in physiology, biochemistry, or behavior with age, but almost no studies demonstrate such changes being predictive of aging. We subsampled from 10 genetically distinct strains of Drosophila melanogaster as they aged, at three time points, measuring change over time of parameters related to water balance (water content, desiccation survival, and K(+), Mg(2+), and Ca(2+) levels). We then determined whether the change over time in any parameters is predictive of mean life span or time of onset of aging. We observed a schedule of aging-related changes. Time of onset of aging was negatively correlated with decline in desiccation resistance and with decline in K(+) between days 0 and 15, and was positively correlated with decline in Ca(2+) between days 15 and 24. We suggest that the potassium result, at least, may be due to loss of functional cytoplasm. We also discuss the use of different estimates of aging in the context of this study.