Heat During Development Can Dull Blue Morpho Butterflies’ Shimmer

Blue morpho butterflies may lose some of their famous brilliance when exposed to high temperatures during development, according to an experiment by researchers at the Smithsonian Tropical Research Institute. The findings were reported in the journal PNAS Nexus. Researchers exposed Morpho helenor pupae to three temperature ranges: conditions typical of their tropical habitat, temperate conditions, and hotter conditions representing temperatures projected under climate change. Pupae kept at temperate and hot temperatures took longer to develop. Deaths were also more frequent among those exposed to the hottest conditions. The adult butterflies that emerged from the heat-exposed pupae had duller iridescence. Researchers found that common bird predators and other butterflies of the same species could detect a change in their color, although the experiment did not establish how that difference might affect survival or reproduction. The blue appearance of morpho butterflies is not produced by pigment. Instead, it results from the way light reflects from microscopic ridged structures on their wing scales. The scales overlap in a pattern compared by the researchers to roof tiles. The researchers said the heat-related color change may be partly linked to a reduction in the spacing between these nanostructures, which can narrow the scales and reduce the amount of overlap. That alteration changes how the structures reflect light. It is still unknown whether less-brilliant wings make the butterflies easier for predators to catch or affect their attractiveness to potential mates. Lead author Juliette Rubin said the results show that the environmental conditions animals experience while developing can alter the color and brightness of iridescent displays. The study provides evidence that even the microscopic structures responsible for an animal’s appearance can respond to developmental temperatures. The researchers said the findings may help in assessing how rising temperatures could affect similar structures in other animals.