DOI: 10.5061/dryad.zpc866t72
title: Thermal response of two sexually dimorphic Calopteryx (Odonata) over an ambient temperature range

description: 1. Organisms may internally or behaviourally 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
 standardised 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 standardised 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.
description: This study was conducted at
 three sites along the AuSable River near Grayling, MI, USA (Finley’s
 Riverside Cabins [N = 589]: 44.657871, -84.728130; Burton’s Landing [N =
 66]: 44.663861, -84.647406; Keystone Landing [N = 538]: 44.665036,
 -84.627466) from June 25 to July 2, 2018 between 0800 and 1800 h. At these
 sites, the river was slow-moving and variable but mostly shallow in depth
 (0.5-1.5 m). Streams were 10-30 m wide, so damselflies were commonly
 exposed to full sun. These damselflies basked on vegetation along the
 banks and in the stream on rocks and debris dams, some of which had live
 vegetation. They roosted overnight in trees along the stream, and adult
 females oviposited in submerged vegetation. <i>C. aequabilis
 </i>was more common in faster flowing water (Burton’s Landing and
 Keystone Landing), and <i>C. aequabilis </i>females were most
 scarce. Otherwise, all damselflies were extremely plentiful.
 Surface temperature of
 perching damselflies was quantified from 20-30 cm distance with an
 infrared thermal camera (Seek Thermal Compact Pro) attached to the
 lightning port of an iPhone 6s (Apple). Thorax surface temperatures were
 measured using “Hi/Lo” mode (16:9 aspect ratio), as the thorax was usually
 the hottest point in the frame. Thorax temperatures of 89 <i>C.
 aequabilis </i>females, 294 <i>C. aequabilis</i> males,
 324 <i>C. maculata</i> females, and 485 <i>C.
 maculata</i> males were measured. Only hardened adult individuals
 were measured (i.e., no tenerals). For a subset of individuals (N = 409),
 wing temperature was also recorded with manual “Spot” mode pointed at
 melanised regions. Damselflies were not marked, so individuals may have
 been measured more than once. However, the large population greatly
 decreased this chance of pseudoreplication. Ambient air temperature was
 simultaneously measured within 1 m of each individual with a digital
 thermometer (Nielson-Kellerman Kestrel 3000 Pocket Weather
 Meter).
description: Wing temperature
 data was not recorded for many individuals. For a subset of individuals
 (N=409), we recorded wing temperature and thorax temperature with the
 thermal camera. However, we chose to only analyse thorax temperatures in
 our study; we had a much larger sample size and there is a strong Pearson
 correlation with thorax temperature (r=0.754). Additionally, using the
 “Hi/Lo” (automatic) setting on the infrared camera to quantify thorax
 temperature was much easier/quicker than the “Spot” (manual) setting
 needed to find the wing temperature. The thorax temperature was found very
 quickly as the hottest point in the frame, while the wing temperature
 needed to be found manually with a different setting. So, we chose to
 maximise our sample size by using the automatic setting to measure thorax
 temperatures and only measuring the wing temperature of damselflies that
 perched for a long time. <br> <br>