Thermal response of two sexually dimorphic Calopteryx (Odonata) over an ambient temperature range

1. Organisms may internally or behaviorally regulate their body temperatures or conform to the ambient air temperatures. Previous evidence is mixed on whether wing pigmentation influences thermoregulation in various odonates. 2. We investigated the thermal response of sympatric North American Calopteryx aequabilis and Calopteryx maculata with a thermal imaging study across a 25°C ambient temperature range. 3. We found that regressions of thorax temperature on ambient temperature standardized by species had similar slopes for male and female C. maculata, but females were consistently 1.5°C warmer than males. In contrast, the sexes of C. aequabilis differed in slope, with C. aequabilis females having a slope less than 1.0 and males having a slope greater than 1.0. 4. We found that regressions of thorax temperature on ambient temperature standardized by sex had similar slopes for males and females of both species, but C. maculata females were consistently 2.1°C warmer than C. aequabilis females. 5. Given that C. aequabilis is strongly sexually dimorphic in pigment, but C. maculata is not, our findings suggest that wing pigmentation may influence thermal response rate in sympatric populations of both species.