Collaborative Research: An Integrative Field and Biophysical Model of Thermal Stress, Physiological Performance, and Reproductive Fitness

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Animals experience thermal stress at the extremes of their geographic range. This stress may be compounded by climate change, especially when the geographic range stretches over a large range of latitude. Many species use behavioral thermoregulation to ameliorate heat stress. However, these compensatory behaviors have a cost, as they require the animal to abandon critical behaviors that may only be performed in the hot and stressful habitat. This study investigates these survival/reproductive tradeoffs in fiddler crabs, small semi-terrestrial crabs that occupy shorelines in the tropics and temperate zones. Male fiddler crabs use visual displays to attract mates in the hot, dry intertidal zone, but must periodically retreat to a cool, moist burrow to rehydrate and recover. Each retreat to a burrow requires a cessation of mating behavior. Periodically the males rereat from the hot reproductive areas to rehydrate and feed. This study will determine the tradeoff between thermoregulation and mating performance across a species' geographic range, using both experimental and modeling approaches, under both current and predicted future conditions. Finally, the project will utilize the results of the research on fiddler crabs to increase public interest in science using public outreach activities and the training students at different levels including high school students. Behavioral compensation for thermal stress can lead to a profound but under-investigated tradeoff, as thermoregulatory behaviors are costly. Energetic and thermoregulation costs will generate major reproductive opportunity costs, which can reduce mating success. This project focuses on the fitness consequences of missed mating opportunities associated with thermoregulatory behaviors. These missed opportunities are crucial to understand in the study of mating success in the context of physiological stress and the differences in costs at different latitudes. Understanding the associated reductions in fitness are crucial to fully understand and predict the consequences of climate change on fitness, since heating in lower latitudes may truncate the benefit of mating owing to the increased cost of thermal stress. This proposal takes an integrative approach, combining laboratory measurements, manipulative field experiments, and biophysical modeling to examine the fitness consequences of behavioral thermoregulation. This work, and the resulting model, will be broadly applicable to the study of climate change impacts on ectotherms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.