Metabolic traits:
As with morphological traits, we also examined the effect of egg mass and incubation temperature on metabolic traits across populations. As egg mass increased, ∆mass decreased at the two southern populations, but had no effect in northern populations (Table 2). However, comparison of beta values across sites showed only a significant difference between AP and SR. A positive influence of egg mass on residual yolk mass was observed across all populations except for AP, but differences across populations were not significant. Incubation temperature did not affect ∆mass or ∆BMI at any population, but exerted negative influences on ∆SVL at YK and fat body mass at all populations (Table 2, Figure 3A). On the other hand, there was a significantly positive influence of incubation temperature on ∆TG and residual yolk mass (Table 2, Figure 3B) in at least one population. Whereas the effect sizes of temperature on ∆SVL, ∆TG and fat body mass did not differ across sites, the influence of temperature on residual yolk mass did, showing a reduction at YK (Table 2, Figure 3B).
When comparing phenotypes across populations after correcting for egg mass, we found significant differences in fat body mass between at least two populations at both 29.5°C and 33.5°C, with a trend for smaller fat body masses at the northern populations (Figure 3A; Appendix 1). Consistent with the decreased influence of incubation temperature on residual yolk mass at YK, animals from 29.5°C at YK had significantly higher residual yolk mass compared to WO (Figure 3B, Appendix 1). Upon examination of the mass-corrected allocation of maternal resources towards metabolic phenotypes, there were significant differences for both residual yolk mass and fat body mass across populations. Animals from the southern populations tended to allocate more resources towards fat body mass than the northern populations (Figure 3C), and animals from YK at 29.5°C allocated more resources towards residual yolk mass relative to other populations (Figure 3D).
Incubation temperature had a negative influence on incubation duration across all sites (Figure 4). The influence of temperature was greater at the northern populations than at southern populations, driven by comparatively shorter incubation periods at 33.5°C and longer incubation periods at 29.5°C (Figure 4). However, differences across sites within temperatures were not significant.