Data from: Body size rather than reflectivity explains thermal constraints on colour variation in an aposematic jewel bug
Data files
Jul 01, 2025 version files 16.27 MB
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bug_pics.zip
15.54 MB
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heating_data.zip
102.95 KB
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README.md
3.56 KB
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specs.xlsx
563.22 KB
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tectocoris_analysis.Rmd
40.68 KB
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tectocoris_data.xlsx
14.09 KB
Abstract
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.
Dataset DOI: 10.5061/dryad.7pvmcvf4j
Description of the data and file structure
- 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.
- 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.
- 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.
- 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
- 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.
- 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:
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.