DOI: 10.5061/dryad.6q573n5xb
title: PCA coordinates describing dorsal colour pattern variation in 723 Morpho butterflies

description: Species interactions such as mimicry can promote trait convergence but
 disentangling this effect from those of shared ecology, evolutionary
 history and niche conservatism is often challenging. Here by focusing on
 wing color pattern variation within and between three butterfly species
 living in sympatry in a large proportion of their range, we tested the
 effect of species interactions on trait diversification. These butterflies
 display a conspicuous iridescent blue coloration on the dorsal side of
 their wings and a cryptic brownish colour on the ventral side. Combined
 with an erratic and fast flight, these color patterns increase the
 difficulty of capture by predators and contribute to the high escape
 abilities of these butterflies. We hypothesize that, beyond their direct
 contribution to predator escape, these wing patterns can be used as
 signals of escape abilities by predators, resulting in positive
 frequency-dependent selection favouring convergence in wing pattern in
 sympatry. To test this hypothesis, we quantified dorsal wing pattern
 variations of 723 butterflies from the three species sampled throughout
 their distribution, including sympatric and allopatric situations and
 compared the phenotypic distances between species, sex and localities. We
 detected a significant effect of localities on colour pattern, and higher
 inter-specific resemblance in sympatry as compared to allopatry,
 consistent with the hypothesis of local convergence of wing patterns. Our
 results provide support to the existence of escape mimicry in the wild and
 stress the importance of estimating trait variation within species to
 understand trait variation between species, and to a larger extent, trait
 diversification at the macro-evolutionary scale.
description: We used the collections of National Natural History Museum of
 Paris to study the variation of colour pattern in the butterfly species
 Morpho helenor, M. achilles and M. deidamia throughout their geographical
 range. Pictures of collection specimens were taken in controlled standard
 white light conditions. The four wings were first manually separated using
 Adobe Photoshop Element. Wing images were then analysed following the
 Colour Pattern Modelling approach (Le Poul et al. 2014) implemented in
 Matlab. This method allows precise comparison of colour pattern while
 accounting for wing shape and venation that might differ between species.
 It has been shown to be especially relevant to quantify similarity and
 differences in color pattern within and across species (Le Poul et al.
 2014; Huber et al. 2015; McClure et al. 2019). Briefly, the algorithm
 detects the four wings on the white background and segments the colour
 pattern in different categories based on pixel densities of the RGB
 values. The number of colours is then set manually: here we chose to
 consider three colours, namely black, blue and white. Some individuals (as
 for instance M. deidamia samples from French Guiana), display a gradient
 of blue that is often detected as a different colour category by CPM. Dark
 blue was nevertheless treated as blue in our analyses. This is probably a
 conservative assumption regarding convergence in colour patterns, because
 the dark blue area of M. deidamia has a similar location to the basal
 black area in M. helenor and M. achilles, and look very dark from
 far-distance. After segmentation, wings were aligned by adjusting
 translation, rotation and scale in order to maximize similarity, allowing
 the colour value for each pixel of the wings to be compared.
description: The dataset provides the PCA coordinates for each of the 723
 Morpho butterflies used in this study, together with information on their
 species, sub-species, sex, sampling zones (using codes defined in the
 associated article), sampling country and exact sampling locality with
 latitudinal and longitudinal localisation.