# Sex-specific effects of protein and carbohydrate intake on reproduction but not lifespan in Drosophila melanogaster

## TL;DR

This study shows that protein and carbohydrate intake affect reproduction differently in male and female fruit flies, but both genders live longest on high-carb, low-protein diets.

## Contribution

The study reveals sex-specific nutritional optima for reproduction and lifespan in fruit flies using the geometric framework.

## Key findings

- Lifespan is maximized with high carbohydrate and low protein intake in both sexes.
- Female reproduction peaks at a 1:2 protein-to-carbohydrate ratio, while males achieve optimal reproduction and lifespan at the same nutrient intake.
- Fruit flies consume a 1:4 protein-to-carbohydrate ratio under dietary choice, failing to reach their optimal nutritional balance for reproduction.

## Abstract

Modest dietary restriction extends lifespan (LS) in a diverse range of taxa and typically has a larger effect in females than males. Traditionally, this has been attributed to a stronger trade-off between LS and reproduction in females than in males that is mediated by the intake of calories. Recent studies, however, suggest that it is the intake of specific nutrients that extends LS and mediates this trade-off. Here, we used the geometric framework (GF) to examine the sex-specific effects of protein (P) and carbohydrate (C) intake on LS and reproduction in Drosophila melanogaster. We found that LS was maximized at a high intake of C and a low intake of P in both sexes, whereas nutrient intake had divergent effects on reproduction. Male offspring production rate and LS were maximized at the same intake of nutrients, whereas female egg production rate was maximized at a high intake of diets with a P:C ratio of 1:2. This resulted in larger differences in nutrient-dependent optima for LS and reproduction in females than in males, as well as an optimal intake of nutrients for lifetime reproduction that differed between the sexes. Under dietary choice, the sexes followed similar feeding trajectories regulated around a P:C ratio of 1:4. Consequently, neither sex reached their nutritional optimum for lifetime reproduction, suggesting intralocus sexual conflict over nutrient optimization. Our study shows clear sex differences in the nutritional requirements of reproduction in D. melanogaster and joins the growing list of studies challenging the role of caloric restriction in extending LS.