Abstract
Sexual dimorphism for lifespan (SDL) is widespread, but poorly understood. A leading hypothesis, which we test here, is that strong SDL can reduce sexual conflict by allowing each sex to maximize its sex-specific fitness. We used replicated experimental evolution lines of the fruit fly, Drosophila melanogaster, which had been maintained for over 360 generations on either unpredictable ‘Random’ or predictable ‘Regular’ feeding regimes. This evolutionary manipulation of feeding regime led to robust, enhanced SDL in Random over control, Regular lines. Enhanced SDL was associated with a significant increase in the fitness of focal males, tested with wild-type (WT) females. This was due to sex-specific changes to male life history, manifested as increased early reproductive output and reduced survival. In contrast, focal female fitness, tested with WT males, did not differ across regimes. Hence increased SDL was associated with a reduction in sexual conflict, which increased male fitness and maintained fitness in females. Differences in SDL were not associated with developmental time or developmental survival. Overall, the results showed that the expression of enhanced SDL, resulting from experimental evolution of feeding regimes, was associated with male-specific changes in life history, leading to increased fitness and reduced sexual conflict.
Highlights
In the more than half a century since the major tenets of the evolutionary theory of ageing were formulated [1,2,3], a huge body of supporting empirical evidence has been gathered [4,5,6,7,8,9]
Data from an initial pilot experiment conducted with once-mated females and males were consistent with this idea and showed that lines maintained on a random, unpredictable feeding regime had evolved significantly enhanced sexual dimorphism for lifespan (SDL) in comparison to control lines fed according to a regular feeding regime
We subjected lines to evolutionary manipulation of randomly within a 28-day cycle (Random) and regularly each week (Regular) feeding regimes and found that this led to enhanced SDL in the Random regime
Summary
In the more than half a century since the major tenets of the evolutionary theory of ageing were formulated [1,2,3], a huge body of supporting empirical evidence has been gathered [4,5,6,7,8,9]. One leading hypothesis, which we test here, is that enhanced SDL could be a mechanism by which sexual conflict is reduced, by allowing females and males to express sex-specific life histories and increase their sex-specific fitness [11,15,30]. This knowledge gap has partly arisen from the lack of an appropriate empirical system in which to test these predictions We address this omission by using lines of D. melanogaster fruit flies subjected to replicated experimental evolution for .360 generations (over 15 years) under divergent random and regular feeding regimes. We used the Random and Regular feeding lines to test the prediction that increased SDL, as expressed by Random in comparison to Regular lines, is associated with decreased 2 sexual conflict through adoption of sex-specific life histories that lead to higher fitness for males and females. We conducted separate experiments to measure the lifespan and fitness of focal females and males from the Random and Regular lines held with non-focal standard wild-type (WT) individuals
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