Offspring wet weight and fat
Across all treatments, wet weight of pupae increased and then declined
with maternal age until the end of the experiment (Fig. 3). Model
selection results provided strong evidence for a quadratic effect of
maternal age on offspring wet weight (control – quadratic effect
including random intercept and slope ω = 0.719; mating delay –
quadratic effect with random intercept and slope ω = 0.562,
without random slope ω = 0.272; and nutritional stress –
quadratic effect with random intercept and slope ω = 0.866)
(Tables S6 7-9). There was no support for a log, or a linear effect of
maternal age for any of the treatments (ω = 0.000).
In addition, across treatments,
the predicted effect of mother age at the population level, assuming a
quadratic fit, was within the standard errors of predictions from GAM
fits to the data (S8 File).
The fitted quadratic curves and coefficients were similar between
treatments (from the model with lowest AIC, which included a random
intercept and slope, coefficient for maternal age: control 0.520 (0.466
– 0.574); mating delay 0.564 (0.406 – 0.723); and nutritional stress
0.502 (0.420 – 0.584), coefficient for maternal age squared: control
-0.0040 (-0.0045 – -0.0035); mating delay -0.0042 (-0.0054 – -0.0030);
and nutritional stress -0.0040 (-0.0048 – -0.0032)) (Tables S6 10 -
12).
For all three treatments, there was strong evidence for individual
variation among mothers in the wet weight of their pupae (for all
treatments, all models without random effects ω = 0.000). This
variation was highest in the mating delay treatment with a random
intercept variance from the most parsimonious model of 11.820, compared
with 7.307 for the control and 2.379 for the nutritional stress
treatment (Tables S6 13 - 15).
There was evidence for variation among mothers in the effect of maternal
age on wet weight for the control and nutritional stress treatments
(quadratic fit with random intercept and slope: control ω =
0.719; and nutritional stress ω = 0.866). There was less support
for this in the mating delay treatment (quadratic fit with random
intercept and slope ω = 0.562, next lowest AIC model - quadratic
fit with random intercept only ω = 0.272).
Offspring fat increased linearly with offspring wet weight (Pearson’s
correlation coefficient 0.554) (File S9), thus for brevity we focus on
wet weight as our trait of interest, but the patterns are qualitatively
similar if offspring fat is considered instead.