DOI: 10.5061/dryad.7pvmcvf4j
title: Data from: Body size rather than reflectivity explains thermal constraints on colour variation in an aposematic jewel bug

description: Theory posits that warning signals should converge phenotypically to
 reinforce predator memory, yet many aposematic species show substantial
 variation in warning signals within and between populations. This may
 reflect alternative selection pressures, such as thermoregulation, though
 empirical tests are limited and often overlook the full solar spectrum. We
 tested whether thermal trade-offs could explain warning colour variation
 in the aposematic cotton harlequin bug (Tectocoris diophthalmus), which is
 sexually dichromatic, varies within sexes, and shows clinal shifts in
 colour—iridescent blue-green in cooler regions, red–orange in warmer ones.
 We measured reflectivity across the full solar spectrum and assessed the
 role of ultraviolet–visible (300–700 nm) and near-infrared (700–1700 nm)
 light on heating, using a solar simulator and temperature
 controlled-chamber to isolate the effect of radiative
 heating. Reflectivity differences between iridescent and
 non-iridescent patches were greatest in the NIR, but these did not
 translate into significant heating differences. However, reflectivity was
 tightly linked to body size, with smaller males reflecting less and
 heating faster. Given the strong correlation between colour and body size,
 thermal constraints may contribute to clinal colour variation.
description: We measured the total hemispherical reflectance for a subset of
 individuals (n = 11), using an integrating sphere. We measured reflectance
 of the spectral range of 400–2100 nm, and measurements were calibrated
 against a 99% white reflectance standard and a 2% black reflectance
 standard. We measured the bugs alive and immediately after euthanasia to
 validate that reflectance remained similar post-mortem. Although our
 reflectance measurements do not include UV, our multispectral imaging
 showed that the bugs do not reflect UV and thus there is no difference in
 UV reflectance. We conducted heating experiments using
 a solar simulator and a closed glass thermal chamber which kept the
 ambient air temperature in the chamber constant at 20º C. This was to
 isolate the effect of radiation from the solar simulator and to minimise
 the effects of convection and conduction. Inside the chamber, the sample
 bug was placed dorsal side up on a transparent acrylic platform and with a
 thermocouple inserted in the posterior to record body temperature.
 Temperature readings of both the air and the bug were taken every 10 s
 using a digital thermometer. We ran each individual sample once for each
 heating treatment: full (300–1700 nanometres), NIR (700–1700 nm), and
 UV–visible (300–700 nm). We used optical filters over the silicon window
 to isolate the effect of radiation in different wavelength ranges. After
 placing the bug in the chamber, we allowed a 10 min period for the bug and
 air to achieve an equilibrium temperature of 20º C. We then opened the
 solar simulator shutter to begin the 10 min heating period. Although each
 heating trial ran for 10 min, all bugs reached a stable maximum
 temperature by 5 min; therefore, all heating estimates were calculated
 based on the first 5 min of the heating period.
description: # Body size rather than reflectivity explains thermal constraints on
 colour variation in an aposematic jewel bug Dataset DOI:
 [10.5061/dryad.7pvmcvf4j](10.5061/dryad.7pvmcvf4j) ## Description of the
 data and file structure 1. **tectocoris_analysis.Rmd** - code for all
 analyses (reflectivity, heating, and statistical). NOTE: In order for all
 code to run, please unzip the two zip files (heating_data.zip and
 bug_pics.zip) located in the "data" folder. 2. **specs.xlsx** -
 raw data from spectrophometer readings, with 3 tabs: * **bug_specs**
 contains the spectrophotometer readings from the bugs. The first column
 "wl" represents wavelength in nanometres. Each subsequent column
 corresponds an individual reflectance measurement of bugs colour patch and
 shows reflectance (%) at each wavelength. * Column names follow the naming
 convention: bug ID, sex, status (all bugs are dead in this dataset),
 colour category of the measured patch, and the spec ID (eg.
 "Splice17__0__03" or "Splice17__1__09"). Examples are:
 "39male_dead_blue_Splice17__1__04" or
 "40female_dead_orange_Splice17__0__00". Respectively, this
 represents a measurement of a blue patch on bug 39male and an orange patch
 on bug 40female. * **irradiance** contains the irradiance spectra obtained
 from the solar simulator manufacturer. The column "wl"
 represents wavelength in nanometres, while "goballrrad"
 represents the irradiance at that wavelength. * **filter_transmittance**
 contains the filter transmittance data. The column "wl" is
 wavelength in nanometres, with "halfsun" = full spectrum
 transmittance, "visfilterTransmittance" = visible wavelength
 transmittance, and "nirfilterTransmittance" = near infrared
 transmittance. 3. **tectocoris_data.xlsx** - data about the bug ID, sex,
 body size, and proportion of iridescence/non-iridescence (taken from image
 data, which is not included but is available on request). Columns are: *
 "bugID" - bug ID * "morph" - classification of colour
 by eye * "colour" - binary classification of majority colour
 using "morph" * "sex" - sex * "area_mm2" -
 area of the bug in mm^2 * "area_iridescent_mm2" - area of the
 iridescent patches in mm^2 * "area_noniridescent_mm2" - area of
 the non-iridescent patches in mm^2 * "proportion_iridescent" -
 proportion of iridescent patches calculated by
 *area_iridescent_mm2/area_mm2* * "proportion_noniridescent" -
 proportion of noniridescent patches calculated by
 *area_noniridescent_mm2/area_mm2* 4. **heating_data.zip** - when unzipped,
 this folder contains the temperature readings from heating experiments. It
 includes 129 .csv files named in the format: treatment_bugID; eg.
 full_01male. Possible treatments include full (300-1700 nanometres),
 near-infrared (700-1700 nm), and UV-visible (300-700 nm). Column C contain
 the bug temperature readings, while column D contains the air temperature
 readings, in ºC. Other columns include data from the thermocouple but are
 not used in the analysis. 5. **bug_pics.zip** - when unzipped, contains
 cropped images of the bugs used for plotting in figures. ## Code/software
 All analyses was done with R 4.2.3 run in macOS (see
 "tectocoris_analysis.Rmd"). Packages include: ``` library(pavo)
 library(tidyverse) library(corrplot) library(readxl) library(writexl)
 library(lattice) library(modelsummary) library(tinytable) library(ggimage)
 ``` ## Access information Other publicly accessible locations of the data:
 *
 [https://github.com/keilinooi/tectocoris_analysis](https://github.com/keilinooi/tectocoris_analysis)