Abstract
Reproductive output and cognitive performance decline in parallel during aging, but it is unknown whether this reflects a shared genetic architecture or merely the declining force of natural selection acting independently on both traits. We used experimental evolution in Drosophila melanogaster to test for the presence of genetic variation for slowed cognitive aging, and assess its independence from that responsible for other traits' decline with age. Replicate experimental populations experienced either joint selection on learning and reproduction at old age (Old + Learning), selection on late-life reproduction alone (Old), or a standard two-week culture regime (Young). Within 20 generations, the Old + Learning populations evolved a slower decline in learning with age than both the Old and Young populations, revealing genetic variation for cognitive aging. We found little evidence for a genetic correlation between cognitive and demographic aging: although the Old + Learning populations tended to show higher late-life fecundity than Old populations, they did not live longer. Likewise, selection for late reproduction alone did not result in improved late-life learning. Our results demonstrate that Drosophila harbor genetic variation for cognitive aging that is largely independent from genetic variation for demographic aging and suggest that these two aspects of aging may not necessarily follow the same trajectories.
Highlights
Aging is a progressive intrinsic physiological deterioration of an organism with age (Rose 1991), which affects most aspects of its function
Under a positive genetic correlation between cognitive and demographic aging, populations from the Old + Learning regime should have evolved improved late-life fecundity and life span relative to the Old regime. This is because the predicted evolutionary response of demographic traits in the Old + Learning regime would contain a component due to correlated response to selection on learning at old age, which was absent in the Old regime
At the end of selection all Old + Learning populations had higher learning scores than the Old populations (Fig. 1), the interaction between selection regime and generation was not significant in the model that considered the entire course of evolution
Summary
2. If there is a positive genetic correlation between cognitive and demographic aging, populations from the Old regime should have evolved improved learning performance at old age relative to the Young regime, despite not being directly selected for learning. 3. under a positive genetic correlation between cognitive and demographic aging, populations from the Old + Learning regime should have evolved improved late-life fecundity and life span relative to the Old regime. Under a positive genetic correlation between cognitive and demographic aging, populations from the Old + Learning regime should have evolved improved late-life fecundity and life span relative to the Old regime This is because the predicted evolutionary response of demographic traits in the Old + Learning regime would contain a component due to correlated response to selection on learning at old age, which was absent in the Old regime. If there is a trade-off between late-life learning and early-life fecundity, populations from the Old + Learning regime should show lower levels of early-life reproduction than populations from the Old regime
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