DOI: 10.5061/dryad.7wm37pvx4
title: Pretty cool beetles: Can manipulation of visible and near-infrared sunlight prevent overheating?

description: Passive thermoregulation is an important strategy to prevent overheating
 in thermally challenging environments. Can the diversity of optical
 properties found in Christmas beetles (Rutelinae) be an advantage to keep
 cool? We measured changes in temperature of the elytra of 26 species of
 Christmas beetles, exclusively due to direct radiation from a solar
 simulator in visible (VIS: 400–700 nm) and near-infrared (NIR: 700–1700
 nm) wavebands. Then, we evaluated if the optical properties of elytra
 could predict their steady state temperature and heating rates while
 controlling for size. We found that higher absorptivity increases the
 heating rate and final steady state of the beetle elytra in a biologically
 significant range (3 to 5°C). There was substantial variation in the
 absorptivity of Christmas beetle elytra; this variation was achieved by
 different combinations of reflectivity and transmissivity in both VIS and
 NIR. The size was an important factor in predicting the change in
 temperature of the elytra after 5 min (steady state) but not the maximum
 heating rate. Lastly, we show that the presence of the elytra covering the
 body of the beetle can reduce the heating of the body itself. We propose
 that beetle elytra can act as a semi-insulating layer to enable passive
 thermoregulation through high reflectivity of elytra, resulting in low
 absorptivity of solar radiation. Alternatively, if beetle elytra absorb a
 high proportion of solar radiation, they may reduce heat transfer from the
 elytra to the body through behavioural or physiological mechanisms.
description: In this experiment, we correlate the heating of the beetle elytra
 and body with its optical properties.  Thus, our data
 set includes files of the spectral reflectance and transmittance of 26
 species of Christmas beetles measured with a dual spectrometer in the
 range between 400 to 1700 nm. We combined the raw spectra with the
 theoretical irradiance data from the sun and the irradiance of the solar
 simulator used in our experiments (from the manufacturer) to calculate
 reflectivity, transmissivity, and absorptivity. Files and original code
 provided.  On the other hand, the temperature of the
 beetle body and beetle elytra were recorded with thermocouples in a
 controlled environment. We provide the raw data of the temperature for
 each experiment consisting of a cycle of 3 rounds of illumination for 5
 minutes and 10 minutes of darkness in between, where each illumination was
 in a different waveband: total spectrum of the solar simulator, only NIR
 light (700 to 1400 nm) and only visible light (400 to 700 nm). 
 Finally, we also provide two files of the processed consolidated
 data: one for the single elytron experiments and one for the full body
 experiments. In these files, we listed the optical properties, change in
 temperature (both maximum heating rate and total change after 5 minutes),
 and size for each sample. These are the ones used in our statistical
 analysis. Code for the data processing and final analysis is also
 included.
description: All the raw files are in format .csv which should be readable by
 multiple software including office, R, and text processors.
 R and R studio are needed to open the .Rmd original
 code.  We also include a .html interactive version of
 the code for easy implementation.