Hot springs, cool beetles: extraordinary adaptations of a predaceous insect in Yellowstone National Park

Several metazoans live in extreme environments, but relatively little is known about the adaptations that these extremophiles have evolved to tolerate their conditions. The wetsalts tiger beetle, <i>Cicindelidia hemorrhagica</i> (LeConte) (Coleoptera: Cicindelidae), is found in the western USA, including the active geothermal springs in Yellowstone National Park (YNP). Here, we characterize behavioral, ecophysiological, and morphological traits of adult <i>C. hemorrhagica</i> living on hot springs in YNP compared to adults living in a non-hot spring environment in Idaho. Individuals in YNP behaviorally warmed and cooled themselves at surprisingly different frequencies than those in Idaho, with YNP individuals infrequently cooling themselves even though surface temperatures were greater because of geothermal activity and consequent bottom-up heating of individuals compared to the saline-flat habitat in Idaho. After a series of lethal thermal maxima and internal body temperature experiments, our results suggest that an explanation for the differential behavior is that the adult in YNP has evolved increased heat reflectance on the ventral portion of its abdomen. This increased heat reflectance seems to be caused by a physical feature as part of the exoskeleton's ventral abdominal plate, which likely protects the beetle by serving as a heat-resistant shield. The extreme conditions in YNP seem to have selected <i>C. hemorrhagica</i> to be among the most thermophilic insects known.