Flash drought and heat waves influence embryonic development and offspring size in an oviparous ectotherm

Anthropogenic climate change is driving an increase in climate extremes,
including concurrent drought and heat wave events. To understand the
ecological consequences of these events, research is needed to identify
their separate and compound effects on organisms across life stages.
Oviparous species are particularly vulnerable to environmental stress at
the embryonic stage, as embryos are relatively unprotected from hydric and
thermal extremes. The embryonic environment can substantially shape
offspring physiology and fitness. However, the developmental impacts of
extreme climate events, including downstream effects on offspring survival
in the field, are not well described. In this study, we investigated the
independent and interactive effects of flash drought and heat waves during
embryonic development in an oviparous vertebrate model, the painted turtle
(Chrysemys picta). In a fully factorial experiment, we imposed simulated
flash drought and heat wave events and examined the effects on egg mass,
incubation time, and offspring body size. After overwintering in the
laboratory, we conducted a release experiment in the field to measure
early-life survival in an ecologically relevant context. We found that
flash drought and heat wave events interactively influenced egg mass
during late embryonic development, and independently reduced incubation
time and post-overwintering body mass. In addition, smaller individuals
had a lower probability of survival in the field. Our results suggest that
oviparous species will face negative impacts on embryonic development and
early-life traits as compound drought and heat wave events become more
frequent and severe.