High food availability reduced the age at maturity (a,c). In the G1, time to maturity was significantly influenced by an interaction between the parental and the current environments (F1,99 = 5.89, p = 0.02, Cohen's f = 0.14). In the G2, time to maturity was affected by an interaction between the P and G1 environments (F1,184 = 4.17, p = 0.04, Cohen's f = 0.11) as well as the separate effect of the current environment (F1,184 = 98.07, p < 0.001, Cohen's f = 0.70). Collembolans on high food matured equally quickly regardless of the environments of their ancestors but time to maturity for those on low food was influenced by the environments of the two preceding generations (c). Post hoc tests demonstrated that collembolans on low food which had both mothers and grandmothers that were on high food (i.e. the HHL treatment) took longer to mature than collembolans on low food, which had mothers that were on high food but grandmothers that were on low food (i.e. the LHL treatment).
Figure 1. (a,b) Time to maturity and size at maturity in the G1 and (c,d) in the G2. Mean values and 95% confidence intervals are indicated. In (a,b), treatment codes on the x-axes indicate the sequence of food treatments over two consecutive generations: P and (more ...)
Collembolans on low food were approximately 20 per cent shorter in length at maturity than those on high food (MD = 302.78 ± 32.97 µm, Cohen's d = 2.60, 95% CI = 2.22–2.99, F1,184 = 320.91, p < 0.001, Cohen's f = 1.29). The transgenerational factors that influenced time to maturity were not found to produce accompanying differences in size at maturity (influence of maternal environment: F1,184 = 2.30, p = 0.13, Cohen's f = 0.05; influence of grandmaternal environment: F1,184 = 0.36, p = 0.55, Cohen's f < 0.01; b,d). Furthermore, neither time to maturity nor size at maturity was significantly influenced by egg size, hatchling length, mother's or grandmother's size at maturity, the size of the mother's or the grandmother's first clutch or the total number of eggs produced by the mother or grandmother (p > 0.15 in all cases).
In the G2, both the maternal environment (F1,184 = 5.12, p = 0.02, Cohen's f = 0.09) and the current environment (F1,184 = 375.27, p < 0.001, Cohen's f = 1.36) influenced the number of eggs in the first clutch (a). In addition, the interactions between the P and G2 environments (F1,184 = 3.50, p = 0.062, Cohen's f = 0.07) and the G1 and G2 environments (F1,184 = 3.30, p = 0.070, Cohen's f = 0.06) were marginally non-significant. Collembolans on high food tended to lay more eggs in their first clutches if their mothers were also recipients of high food. Collembolans on high food which had both mothers and grandmothers on low food (i.e. in the LLH treatment) laid an average of 4.33 ± 2.64 fewer eggs than those in the LHH treatment (Cohen's d = 1.11, 95% CI = 0.51 – 1.71) and 3.53 ± 2.72 fewer eggs than those in the HHH treatment (Cohen's d = 0.85, 95% CI = 0.25–1.44). The number of eggs laid in the first clutch was lower for collembolans on low food and no effect of maternal or grandmaternal environment was detected in the four low-food treatments that were applied in the G2 (a). Furthermore, collembolans on high food regimes also tended to produce more clutches (MD of 0.86 ± 0.26 clutches, t190 = 6.54, p < 0.001, Cohen's d = 0.94 with 95% CI of 0.64 – 1.24) and there was evidence that this effect spanned the generations (b) as the main effects of the P environment (F1,184 = 4.44, p = 0.036, Cohen's f = 0.12), G1 environment (F1,184 = 6.17, p = 0.014, Cohen's f = 0.15) and G2 environment (F1,184 = 43.78, p < 0.001, Cohen's f = 0.46) were all significant (while p > 0.35 for all interactive terms). However, this effect on number of clutches did not translate into differences in reproductive success (as measured by eggs produced) as the G2 environment was the only significant effect (F1,184 = 489, p < 0.001, Cohen's f = 1.60; p > 0.24 for all other terms in the model). Finally, high food availability increased mortality within a generation (by up to 9.4 times, 95% CI = 2.14 – 41.51, Wald1 = 19.01, p < 0.01) but had no detectable influence across generations (maternal influence: Wald1 = 0.92, p = 0.34; grandmaternal influence: Wald1 = 0.46, p = 0.50).
Figure 2. Mean number ± 95% confidence intervals of (a) eggs laid in the first clutch and (b) clutches laid during the first 46 days of life by collembolans within the various treatments of the G2. Treatment codes on the x-axes indicate the sequence of (more ...)
Quantitatively and qualitatively similar results were recorded for the other three strains (and these results are set out in the electronic supplementary material).