This manuscript tests the hypothesis that different species of Morpho butterflies are more similar than expected in sympatry. They use image analysis of museum specimens, and found that although there were significant differences in colour pattern between locations, these were not correlated with any obvious environmental differences. They rather found support for the idea that the three species were more similar than expected when sympatric, consistent with predictions from positive frequency-dependent selection on colour pattern (Müllerian mimicry).

Overall I felt this study was nicely done. I don't see any problems with methods of pattern analysis and I liked the fact that randomization tests were used to determine if species pairs were more or less similar than expected. My main concerns with the manuscript are rather related to the presentation of the results. For one thing, the discussion is very narrowly-focused on the particular study species. I would have liked to have seen a broader discussion connecting these results to those in other systems. Related to this, I felt it wasn't really clear what the main novelty of the results was. How does this add to what is already known about selection for mimicry? Is it just the fact that similar results were obtained for a group where bright colouration signals escape ability rather than unpalatability? If so, then this study is certainly publishable, but not really a major contribution to the literature.