Morphological traits:
Both egg mass and temperature exerted positive effects on hatchling mass
across all populations (Table 2). However, whereas the influence of egg
mass did not differ across sites (Figure 2A), temperature more strongly
affected hatchling mass at YK compared to the other three populations
(Figure 2B). In addition, there was a trend for a greater influence of
incubation temperature on SVL at the northern populations relative to
the southern populations, with the influence of temperature on SVL not
significant in the latter (Figure 2C). Across other morphological
traits, the influence of temperature was variable in both direction and
magnitude, differentially affecting TG, HL, and HW in at least one
population, while the influence of egg mass was not (Table 2).
We next examined the extent to which morphological phenotypes varied
across populations within a temperature, including whether differences
in the influence of incubation temperature were driven by variation at
33.5°C, 29.5°C, or both by comparing model means under a common egg
mass. There were significant differences in trait values between at
least two populations for all morphological traits after controlling for
egg mass differences, with interpopulation variation in morphological
traits occurring primarily at 29.5°C (Appendix 1). For instance, the
influence of incubation temperature on mass of YK hatchlings was
primarily driven by a reduction in mass at 29.5°C relative to the other
populations (Figure 2B). This pattern was mostly consistent across
additional traits that were differentially impacted by incubation
temperature in at least one population (TG, HL, and HW), with the
exception of SVL, which appeared to involve differences at both 29.5°C
and 33.5°C (Figure 2C). Ratios of morphological traits to hatchling mass
showed no significant differences across populations at either
temperature.