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Reproductive output is often constrained by availability of macronutrients, especially protein. Long-term protein restriction, therefore, is expected to select for traits maximizing reproduction even under nutritional challenge. We subjected four replicate populations of Drosophila melanogaster to a complete deprivation of yeast supplement, thereby mimicking a protein-restricted ecology.Following 24 generations, compared to their matched controls, females from experimental populations showed increased reproductive output early in life, both in presence and absence of yeast supplement. The observed increase in reproductive output was without associated alterations in egg size, development time, preadult survivorship, body mass at eclosion, and life span of the females. Further, selection was ineffective on lifelong cumulative fecundity. However, females from experiment regime were found to have a significantly faster rate of reproductive senescence following the attainment of the reproductive peak early in life. Therefore, adaptation to yeast deprivation ecology in our study involved a novel reproductive strategy whereby females attained higher reproductive output early in life followed by faster reproductive aging. To the best of our knowledge, this is one of the cleanest demonstrations of optimization of fitness by fine-tuning of reproductive schedule during adaptation to a prolonged nutritional deprivation.

Interlocus sexual conflict (ISC) arises due to antagonistic interactions between the sexes. Recent evidence suggests that the intensity of ISC could reduce due to habitat complexity and spatial structure, especially if it results in reduced encounter rate between sexes. Hence, spatial structuring, a common attribute of most natural populations, can potentially bring down the intensity of ISC. We tested this theory using laboratory populations of Drosophila melanogaster. We set up cohorts in three-patch habitat systems as either interconnected (structured) or unconnected (unstructured). Following a fully crossed design, we measured ISC by comparing reproductive output and starvation resistance of singly mated females and those continuously housed with surplus males. We show that continued exposure to males leads to significant fitness costs, indicating ISC. The experimental habitat type did not affect ISC. However, we found significant reproductive and survival costs arising from structured population. Our results are also robust to the alteration in female condition. Therefore, it appears that spatial structure per se cannot decrease ISC, but impose additional survival costs. We further showed such survival cost to be sex-specific, possibly reflecting female-biased spontaneous dispersal.

Dietary restriction is a common ecological challenge that limits reproduction. Yet only a few studies have explored adaptation under chronic protein deprivation. We subjected four replicate laboratory-adapted populations (YLB) of Drosophila melanogaster to a complete deprivation of live-yeast to mimic diet restricted ecology. In this insect, live-yeast is a critical source of protein that strongly affect reproductive output, especially in females. Following 24 generations of experimental evolution, compared to their matched controls (BL), females from YLB populations showed increase in reproductive output early in life, both in presence and absence of live-yeast. The observed increase in reproductive output was not associated with any accommodating alteration in average egg size; and development time, pre-adult survivorship, and body mass at eclosion of the progeny. Interestingly, adult lifespan was also found to be unaffected. However, YLB females were found to have a significantly faster rate of reproductive senescence albeit without any change in a measure of lifetime reproductive output. Taken together, adaptation to LYD ecology shows that reproductive output can evolve without affecting lifespan, suggesting that widely observed reproduction-survival trade-off is not universal. Populations can optimize fitness by fine tuning the scheduling of reproduction even when lifetime reproductive output is constrained.