Thermoregulatory adaptations of the wetsalts tiger beetle, Cicindelidia haemorrhagica, in Yellowstone National Park

Abstract

The wetsalts tiger beetle, Cicindelidia haemorrhagica (LeConte) is found throughout Yellowstone National Park (YNP) associated with active thermal hot spring areas with surface temperatures that exceed 50 °C. Previous studies suggest that YNP C. haemorrhagica behaviorally thermoregulate differently than populations from Idaho not associated with hot springs. However, the cause of this behavioral difference is unknown. Therefore, our study had five objectives: 1) compare internal temperatures of YNP and Idaho adult C. haemorrhagica in similar environmental conditions; 2) determine if the cuticular wax influences YNP beetle internal body temperature; 3) measure and analyze venter reflectivity of YNP and Idaho beetles; 4) compare YNP and Idaho beetle abdominal structures using scanning electron microscopy; and 5) analyze thermal video recordings of YNP adults to estimate times spent on different surface temperatures. Internal temperatures of freshly killed adults were recorded using thermocouples inserted into the abdomen and were suspended over a heated water bath. Our results found a mean difference of 1.03 °C between YNP and Idaho beetle internal temperatures, suggesting that the exoskeleton reflects more heat in YNP adults. Our results suggest that the wax does not play a significant role in temperature reduction. The dissected exoskeletal ventral abdominal face experienced a mean difference of 0.58 °C compared to an imitation venter, suggesting the venter was primarily responsible for heat reflection. Spectrophotometric differences revealed greater reflective properties of YNP beetle venters. Scanning electron microscopic images indicated no visible structural differences between YNP and Idaho beetles. Thermal video analysis indicated YNP adults spent an increasing amount of time on surface temperatures greater than 20 °C, but decreasing amounts of time on surfaces temperatures greater than 40 °C. Beetles from only one YNP location were on surfaces exceeding 50 °C. Our results suggest that physical properties of the abdominal venter of YNP beetles are likely responsible for improved heat reflection from bottom-up heating of hot spring areas. Improved heat reflection resulted in lower internal temperatures of YNP beetles relative to Idaho.