COS 23-6
Sublethal warming in the nest affects embryo physiology and post-hatching phenotypes in the Eastern fence lizard (Sceloporus undulatus)
Sublethal stressors will likely mediate an organism’s response to climate change. Mobile animals can use behavioral thermoregulation to buffer effects of environmental changes, but animals in sessile stages of ontogeny are particularly vulnerable to warming. For example, lizard embryos are exposed to recurrent thermal stress as they develop in shallow nests. Acute exposures to nest temperatures above 41.5°C can be lethal to Eastern fence lizard (Sceloporus undulatus) embryos. Although 41.5°C is beyond the range experienced in contemporary climates, rapid warming will push nest conditions closer to critical limits. Therefore, it is important to examine how recurrent exposure to sublethal high temperatures affects embryos. We reared S. undulatus embryos under three thermal regimes based on soil temperature data from nest sites in SC. Treatments included a contemporary scenario with a maximum daily temperature (Tmax) of 32.1°C, and two in which Tmax was increased by +3.5°C and +7.0°C to simulate warming scenarios. Clutches were divided evenly among treatments to examine impacts of the thermal regimes on embryo physiology. Upon hatching, lizards were transferred to a common environment to examine effects on hatchling phenotypes. During incubation, we measured embryo heart rates, growth, and survival. After hatching, we measured hatchling metabolic rates and growth.
Results/Conclusions
Embryo survivorship decreased significantly in warming treatments, with the lowest survival in the +7.0°C treatment. Eggs in warmer nests gained mass more quickly, but further analysis is needed to determine if the difference was due to increased embryo growth rates or water absorption by eggs. Lizards from both warming treatments hatched significantly smaller in mass and SVL, and they grew at slower rates than hatchlings from the contemporary treatment. The effects on hatchling size and growth rates were greatest for the +7.0°C treatment. Thus, lizards from warmer nests hatched smaller and remained smaller compared to those from the contemporary treatment. Week-old hatchlings from both warming treatments had significantly lower metabolic rates than hatchlings from the contemporary treatment, indicating a potential acclimation response to a warmer nest environment. However, decreased survivorship, hatchling size, and hatchling growth suggest acclimation in the nest may not be enough to overcome increased costs associated with sublethal warming in the nest. Therefore, thermal constraints on embryo physiology may limit persistence of S. undulatus under climate warming.