Meeting Abstract
As climate change drives historically stable air temperatures upward, the effects on ectotherms may be severe. Animal body size affects responses to many environmental factors; however, it is not clear whether body size affects organismal responses to environmental temperature. Recent studies (Oyen et al. 2016; Kaspari et al. 2015), found that organisms could survive higher air temperatures during thermal ramping, but attributed these size effects to biophysical factors such as larger ants having longer legs and larger bees being slower to equilibrate while ramping. We determined the acute critical thermal maximum temperatures for orchid bees (n=61) that varied in body mass from 0.0573-1.0248 grams. Orchid bees were caught by baiting to odor compounds in Gamboa, Panama. Bees were immediately transported to a lab at The Smithsonian Tropical Research Institute in Gamboa where we placed them in a small arena inside a sealed styrofoam cooler. We continuously measured air temperature as it was ramped upward, recorded changes in behavior relevant to thermoregulation throughout warming, and measured air and bee thorax temperatures using a grab and stab method immediately following death. We found that larger orchid bees had slightly higher critical thermal maxima than smaller bees. Contrary to the prior cited studies, our results cannot be explained by biophysical factors, since unlike prior studies, we measured body temperatures at the time of death and these were higher in larger bees. Also, the elevation of body above air temperature increased in larger bees. We hypothesize that, since larger bees are warmer than the smaller bees at all air temperatures, that larger bees may have evolved the ability to tolerate higher body temperatures, they might be less sensitive to elevated air temperatures.
