Climate change is causing rapid shifts in temperature and precipitation patterns worldwide, including more frequent extreme climate events (ECEs) such as flash droughts and heat waves. ECEs can have severe ecological impacts, as temperature and water availability play critical roles in the survival, growth, and functioning of living organisms. Environmental conditions experienced during embryonic development can have lasting phenotypic and fitness consequences, yet the effects of drought and heat waves at this key life stage are not well defined, particularly in vertebrates. Turtles (order Testudines) are particularly susceptible to early-life impacts of drought and heat waves. Embryos have little protection from unfavorable hydric and thermal conditions in the nest, and overall egg and hatchling mortality is high. In my thesis, I investigated the effects of flash drought and heat waves during embryonic development on offspring traits and survival in two freshwater turtle species. I chose to focus on common snapping turtles (Chelydra serpentina) and painted turtles (Chrysemys picta) in order to compare taxa with contrasting life history traits. For my first chapter, I incubated C. serpentina eggs under varying hydric conditions to simulate flash drought at different embryonic stages and identified time-dependent effects on incubation time and hatchling size. I then conducted an experimental release in the field, which revealed that flash drought during late incubation decreased hatchling survival. For my second chapter, I examined the independent and interactive effects of flash drought and heat wave events during embryonic development in C. picta, finding effects on hatching phenology and body size. Moreover, survival increased with body size during dispersal from the nest. My findings shed light on the potential ecological consequences of extreme climate events in oviparous ground-nesting vertebrates.
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