DOI: 10.5061/dryad.3j9kd51qk
title: Data for: Ebony underpins Batesian mimicry in melanic stoneflies

description: The evolution of Batesian mimicry – whereby harmless species avoid
 predation through their resemblance to harmful species – has long
 intrigued biologists. In rare cases, Batesian mimicry is linked to
 intraspecific colour variation, in which only some individuals within a
 population resemble a noxious ‘model’. Here, we assess intraspecific
 colour variation within a widespread New Zealand stonefly, wherein highly
 melanised individuals of Zelandoperla closely resemble a chemically
 defended aposematic stonefly, Austroperla cyrene. We assess convergence in
 the colour pattern of these two species, compare their relative
 palatability to predators, and use genome-wide association mapping to
 assess the genetic basis of this resemblance. Our analysis reveals that
 melanised Zelandoperla overlap significantly with Austroperla in colour
 space, but are significantly more palatable to predators, implying that
 they are indeed Batesian mimics. Analysis of 194,773 genome-wide SNPs
 reveals an outlier locus (ebony) strongly differentiating melanic versus
 non-melanic Zelandoperla. Genotyping of 338 specimens from a single
 Zelandoperla population indicates that ebony explains nearly 70% of the
 observed variance in melanism. As ebony has a well-documented role in
 insect melanin biosynthesis, our findings indicate this locus has a
 conserved function across deeply divergent hexapod lineages.
 Distributional records suggest a link between the occurrence of melanic
 Zelandoperla and the forested ecosystems where the model Austroperla is
 abundant, suggesting the potential for adaptive shifts in this system
 underpinned by environmental change.
description: Photographs were taken in RAW format using a Canon 40D camera
 with an EF-S 60 mm f/2.8 lens under fixed magnification, exposure time,
 aperture, and ISO sensitivity settings. The average red, green, and blue
 (RGB) colour channel values of each image were then linearised and
 equalised in reference to the nominal RGB values of the grey patches of
 the ColorGauge Pico target in Adobe Photoshop CC 2021. Colour measurements
 were taken from calibrated images in five regions of interest (ROIs) using
 the RGB Measure function in ImageJ. The first three chosen ROIs correspond
 to areas of the head (1), pronotum (2), and femorae (3), to provide a
 broad representation of overall body melanisation. The additional ROIs
 correspond to areas on the foreleg tibiae (4) and forewing bases (5)
 associated with warning colouration in the aposematic model Austroperla.
 Mean RGB values from each ROI were converted to HSB (hue, saturation,
 brightness) values using the colorsys module in Python, and only the
 achromatic brightness values of the five ROIs, within a range of 0%
 (black) to 100% (white), were used in subsequent analyses. A principal
 component analysis (PCA) was performed on brightness data from the three
 ROIs associated with overall body melanisation in a combined dataset (n =
 360) containing Zelandoperla and the aposematic model
 Austroperla.
description: ## Data for: ebony underpins Batesian mimicry in melanic stoneflies This
 dataset contains colour measurement data for 338 Zelandoperla fenestrata
 and 22 Austroperla cyrene stonefly specimens. Photographs were taken in
 RAW format using a Canon 40D camera with an EF-S 60 mm f/2.8 lens under
 fixed magnification, exposure time, aperture, and ISO sensitivity
 settings. The average red, green, and blue (RGB) colour channel values of
 each image were then linearised and equalised in reference to the nominal
 RGB values of the grey patches of the ColorGauge Pico target in Adobe
 Photoshop CC 2021. Colour measurements were taken from calibrated images
 in five regions of interest (ROIs) using the RGB Measure function in
 ImageJ. The first three chosen ROIs correspond to areas of the head (1),
 pronotum (2), and femorae (3), to provide a broad representation of
 overall body melanisation. The additional ROIs correspond to areas on the
 foreleg tibiae (4) and forewing bases (5) associated with warning
 colouration in the aposematic model Austroperla. Mean RGB values from each
 ROI were converted to HSB (hue, saturation, brightness) values using the
 colorsys module in Python, and only the achromatic brightness values of
 the five ROIs, within a range of 0% (black) to 100% (white), were used in
 subsequent analyses. A principal component analysis (PCA) was performed on
 brightness data from the three ROIs associated with overall body
 melanisation in a combined dataset (n = 360) containing Zelandoperla and
 the aposematic model Austroperla. ## Description of the data and file
 structure Tab 1 includes measurements in RGB colour space for five regions
 of interest. Tab 2 includes measurements in HSB colour space for five
 regions of interest. Tab 3 shows the overall melanism index for each
 individual.