DOI: 10.5061/dryad.05qfttf6h
title: Diet quality impairs male and female reproductive performance and affects the opportunity for selection in an insect model

description: Environmental factors can have profound effects on the strength and
 direction of selection and recent studies suggest that such
 environment-dependent selection can be sex-specific. Sexual selection
 theory predicts that male fitness is more condition dependent compared to
 female fitness, suggesting that male fitness is more sensitive to
 environmental stress. However, our knowledge about the effect of
 environmental factors on sex-specific reproductive performance and on sex
 differences in the opportunity for selection is still very limited. In the
 present study, we investigated the sex-specific effects of diet quality
 (yeast deprivation and flour type) in the red flour beetle Tribolium
 castaneum. Specifically, we manipulated yeast supplementation in wheat and
 whole-wheat flour in competition assays allowing to test for sex-specific
 effects of food quality (i) on reproductive success and (ii) on the
 opportunity for selection. Our data show that yeast deprivation in wheat
 flour had significantly negative effects on body mass and reproductive
 success of both sexes, while high quality flour (whole-wheat flour) was
 able to buffer the negative impact to a large extent. Importantly, our
 data suggest no sex-specific effect of dietary stress on reproductive
 success because the magnitude of the negative effect of yeast deprivation
 was similar for males and females. Moreover, our study demonstrates that
 low food quality inflated the opportunity for selection and did not differ
 between sexes neither under benign nor stressful dietary conditions. We
 discuss the implications of our findings for the adaptation to stressful
 environments.
description: Stock cultures and
 experimental cultures were kept in incubators at 30°C (±1°C) at 50%
 humidity (±5%) without light. Experimental procedures were performed at
 room temperature. All flour had been frozen for sterilization prior to
 experiments at -30°C for at least 24h. The Ga1 (wildtype line) and Rd
 (‘reindeer’ mutant line) used in this experiment had been originally
 supplied by the U.S. Department of Agriculture and kept in the laboratory
 for over a year in standard culturing conditions. Rd is a dominant
 mutation that affects antenna morphology and was used as a paternity
 marker. All stock beetles were kept in a flour mixture that consisted of
 organic wheat flour (type 405, Alnatura, Darmstadt, Germany) and 5 % dry
 baker’s yeast. In this study we manipulated the diet in two ways: First,
 we manipulated yeast availability in standard, organic wheat flour (type
 405, Alnatura, Darmstadt, Germany), with either control (5% yeast) or no
 yeast. Secondly, we manipulated yeast availability in organic whole-wheat
 flour (Alnatura, Darmstadt, Germany), with either control (5% yeast), low
 yeast availability (1% yeast) or no yeast. The low yeast availability treatment was with
 1% yeast similar to a previous study (Godwin et al., 2017) but can still
 be considered arbitrary and results might be sensitive to the chosen
 range. Impact of food quality on reproductive
 performance In the first assay, we manipulated the diet
 quality (i.e. yeast availability) of all focal individuals to investigate
 the effect of dietary stress on reproductive success of males and females
 in a setup allowing for intra-sexual competition.
 We set up base cultures of 80
 individuals of Ga1 (wildtype) and Rd adults in each of the treatments.
 Stock adults were left to mate and oviposit for three days in 60 g of
 flour according to treatment, afterwards the adults were discarded and the
 eggs were left to hatch. 31 days after the base cultures had been set up,
 we collected and sexed pupae and established sex-separated groups of 40
 individuals. 8 days after the last pupae had been sexed, all pupae had
 emerged and were fully adult. We then set up the mating groups for the
 experiment. Groups contained the focal individual (female or
 male) and a competitor (Rd), as well as two mating partners. All mating
 group beetles were synchronized in age (±3 days) and competitors as well
 as mating partners were always raised on the control diet. All wildtype
 mating partners were marked with a dot of Revell emaille paint, to
 differentiate them from the focal. We allowed the treatment groups to mate
 undisturbed for three days in empty arenas (plastic Petri dishes, diameter
 3.3 cm). All mating trial arenas were scratched at the bottom to increase
 traction for the beetles and contained no flour to prevent oviposition.
 After the mating trial, we froze the males at -30°C for preservation to
 take phenotypic measurements (see below), while we separated the females
 to oviposit for 2 weeks in the control environment. In addition, to investigate if females recovered
 from the treatment when returned to the control diet (i.e. 5% yeast) to
 lay eggs, we transferred all yeast-deprived females from the whole-wheat
 flour treatment after one week to a new egg-laying vial (see Appendix
 Figure A1). After two
 weeks, females were removed and frozen at -30°C until further processing.
 Once all offspring reached the adult stage after 50 days, they were frozen
 and scored for genotype (wildtype or Rd; with Rd phenotype clearly
 discernible from the wildtype due to shorter and thicker
 antennae). All frozen individuals from the mating groups
 were weighed to the nearest 0.01mg on a Sartorius R200D balance
 (Göttingen, Germany) within two months after the main experiment.
 Body mass was used as a
 proxy for condition (Rowe
 and Houle, 1996).
 The repeatability of body
 mass, estimated from measuring twice a subset of the samples was high
 (Intra-class correlation coefficient, ICC = 0.937, P &lt; 0.001, N =
 96). Impact of food quality on the opportunity for
 selection In the second assay, we manipulated the diet
 quality (i.e. yeast availability) of all individuals (i.e. focals,
 competitors and mating partners) during development. Hence we mimicked
 population level dietary manipulation, aiming to measure the opportunity
 for selection in males and females separately. After the mating trials,
 all females were given the opportunity to lay eggs on their respective
 rearing diet (control or yeast deprived). Apart from this, the
 experimental design followed the procedures described above and was
 performed in parallel with the first assay.