Data from: Stage-dependence of phenotypical and phenological maternal effects: insight into squamate reptile reproductive strategies

Enhanced thermal conditions have been credited as a driving force for the
evolution of viviparity, particularly in squamate reptiles, among which it
has independently evolved more than 100 times. However, maternal
thermoregulation is also a critical component of reproduction in oviparous
squamates, for which considerable embryonic development occurs prior to
oviposition. When carrying eggs, oviparous mothers modify thermoregulation
in a manner similar to that of pregnant females. To further understand the
role of temperature in influencing reproductive strategies, it is critical
that we elucidate the degree to which thermal sensitivity varies across
developmental stages. We studied stage-dependent embryonic sensitivity in
a viviparous snake, the aspic viper (Vipera aspis). We manipulated female
body temperature at different stages of pregnancy—early development, early
embryonic growth, and late embryonic growth—by imposing two contrasting
daily thermal cycles that mimicked reproductive (warm) and nonreproductive
(cool) female temperature profiles. Thermal sensitivity of offspring
phenotype was stage dependent, with offspring quality more negatively
affected when exposure to cool temperatures occurred early in development.
In contrast, developmental rate was slowed by the cooler cycle,
independent of the timing of the exposure. Given the more persistent
effect on phenology, phenological effects likely provide a greater driving
force for complete embryonic retention (i.e., viviparity).