Patterns of physiological decline due to age and selection inDrosophila melanogaster

Abstract

In outbred sexually reproducing populations, age-specific mortality rates reach a plateau in late life following the exponential increase in mortality rates that marks aging. Little is known about what happens to physiology when cohorts transition from aging to late life. We measured age-specific values for starvation resistance, desiccation resistance, time-in-motion, and geotaxis in ten Drosophila melanogaster populations: five populations selected for rapid development and five control populations. Adulthood was divided into two stages, the aging phase and the late-life phase according to demographic data. Consistent with previous studies, we found that populations selected for rapid development entered the late-life phase at an earlier age than the controls. Age-specific rates of change for all physiological phenotypes showed differences between the aging phase and the late-life phase. This result suggests that late life is physiologically distinct from aging. The ages of transitions in physiological characteristics from aging to late life statistically match the age at which the demographic transition from aging to late life occurs, in all cases but one. These experimental results support evolutionary theories of late life that depend on patterns of decline and stabilization in the forces of natural selection.

Coenzyme Q and Aging in the Fruit Fly Drosophila melanogaster

“…Populations showed changes in age-specific rates, including differences in starvation resistance, desiccation resistance, time-in-motion and geotaxis. Age at which physiological decline occurs matches with the age at which the transition from exponential mortality to late life occurs (Shahrestani et al 2016). This result suggests that late-life is physiologically distinct from aging.…”

“…However, depending on how a population develops, this is how aging is. Populations selected for fast development (9-10 day generation cycles) during several generations entered the late-life phase at an earlier age than flies selected for slow development (28 day generation cycles) (Shahrestani et al 2016).…”

Evolution, Chance, and Aging

“…Since some individuals continue to live during a period of the life span when deleterious mutations are postulated to accumulate (mutation accumulation) or when mutations manifest their negative effects upon survival (antagonistic pleiotropy), it is postulated that alleles must be present that have adult-persistent positive effects upon survival (or effects within a large age window) ( Charlesworth, 2001 ; Rauser et al, 2006 ). The period with the mortality rate plateau, also called “late life,” has been correlated with a shift in several physiological traits ( Shahrestani et al, 2016 ; Zhang et al, 2016 ).…”

“…An evolutionary perspective provides a potential complication for this point of view ( Rose et al, 2012 ). The mortality rate plateau, which seems to be accompanied by a plateau of at least some types of physiological decline in a model species ( Shahrestani et al, 2016 ), highlights adaptation and selection as part of the aging phenomenon. Throughout most of the reproductive period of adulthood the force of natural selection upon fitness declines, leading potentially to lessened adaptation, which in turn will lead to physiological declines.…”