DOI: 10.5061/dryad.tmpg4f4vs
title: Intralocus sexual conflict over optimal nutrient intake and the evolution of sex differences in lifespan and reproduction

description: Despite widespread variation in lifespan across species, three clear
 patterns exist: sex differences in lifespan are ubiquitous, lifespan is
 commonly traded against reproduction, and nutrition has a major influence
 on these traits and how they trade-off. One process that potentially
 unites these patterns is Intralocus Sexual Conflict (IASC) over the
 optimal intake of nutrients for lifespan and reproduction. If nutrient
 intake has sex-specific effects on lifespan and reproduction and nutrient
 choice is genetically linked across the sexes, IASC will occur and may
 prevent one or both sexes from feeding to their nutritional optima. Here
 we determine whether this process is operating in the cricket Gryllodes
 sigillatus. We show that protein and carbohydrate intake have contrasting
 effects on lifespan and reproduction in the sexes and that there are
 strong positive intersexual genetic correlations for the intake of these
 nutrients under dietary choice. This divergence in nutrient effects,
 combined with the genetic architecture for nutrient choice is predicted to
 accelerate the evolutionary response of nutrient intake in males but
 constrain it in females, suggesting they are losing the conflict.
 Supporting this view, males and females were shown to regulate nutrient
 intake to a common ratio that was not perfectly optimal for lifespan or
 reproduction in either sex, especially in females. Our findings show that
 IASC over the optimal intake of nutrients is likely to be an important
 process generating sex differences in lifespan and reproduction and may
 help explain why females age faster and live shorter than males in G.
 sigillatus.
description: This work consists of 3
 main experiments. In Experiment 1, we examine how the intake of protein
 and carbohydrates influences lifespan and reproduction in male and female
 crickets. The data is analysed using response surface analysis and
 comparisons between the sexes (and across traits within the sexes) are
 characterised using sequential models and the calculation of angles
 between vectors and distances between nutritional optima. In Experiment 2, we examine the
 quantitative genetic basis of protein and carbohydrate intake in males and
 females using 9 inbred lines of crickets. These crickets were given the
 choice between two diets differing in the ratio of protein:carbohydrate
 but with the same caloric content. Genetic estimates were obtained using a
 Bayesian analysis. In Experiment 3, we examined the
 regulated intake point of males and females when given the choice between
 a broader range of diets differing the ratio of protein:carbohydrates and
 total caloric content. This data was analysed using multivariate analysis
 of variance (MANOVA) and analysis of covariance (ANCOVA). Data from Experiments 1 and 2
 were used to estimate the strength of intralocus sexual conflict over the
 optimal intake of nutrients for lifespan. Data from Experiments 1 and 3
 were used to examine how well male and female crickets regulated their
 intake of nutrients relative to the optima for lifespan and
 reproduction.
description: The data from the 3
 experiments are presented as separate worksheet in the Hunt et al_data
 file. In each worksheet, we used the following abbreviations for the
 variables measured: P = protein, C = carbohydrate, LS= lifespan, DRE =
 daily reproductive effort, LRE = lifetime reproductive effort. For each
 variable, if a “Z” is presented in front of the abbreviation it signifies
 that the variable underwent a <i>Z</i> – transformation prior
 to analysis.