There’s more than one way to beat the heat: What anal probes tell us about thermal responses in Neotropical beetles (Coleoptera: Cerambycidae)

Increasing temperatures have been linked to shifts in the distributions and preferred microhabitats of terrestrial species. In ectothermic organisms, intraspecific variation in color can correspond with differences in temperature and humidity, over longitudinal and altitudinal gradients. Microhabitat differences also characterize tropical forests, with canopy stratum being hotter and less humid than ground stratum. This study investigates the relationship between morphological attributes (color lightness, size, and pubescence) and thermal responses, to find clues for behavioral preferences (vertical stratification) in woodboring cerambycid beetles. Preserved specimens (in the subfamilies Cerambycinae and Lamiinae) from Central and South America were selected based on their apparent stratum preferences and heated in a laboratory setting. Color lightness had a significant impact on heating rates: in accordance with the thermal melanism hypothesis, darker specimens heated up more rapidly than lighter ones. Smaller specimens, and specimens with appressed pubescence, reached lower maximum temperatures. These latter results were contrary to expectations based on surface area to volume ratios. Thermal responses involved more complicated relationships with morphological attributes than predicted. Morphological attributes and thermal responses did not differ significantly between strata due to the high levels of variability observed, and small sample size. Further study of the interactions between the factors affecting heating rates of cerambycids, their thermal tolerances, and the abiotic components of their selected microhabitats will be essential to understand the potential impact of climate change.