Home to thousands of species of butterflies, the forests of central and South America are fluttering with color and pattern. Two of those species are Heliconius cydno and Heliconius melpomene. They’re closely related, but live in different microhabitats: Heliconius cydno lives deep in the forest, while Heliconius melpomene lives on its edges. Scientists think that studying their brains can help us understand how the brain is involved in speciation, or the formation of distinct species through evolution.
After studying the butterflies’ brains under a powerful microscope, researchers found that structures in the brain crucial to visual processes such as color vision and shape and motion detection are between 13 and 27% larger in the brains of the species that lives deep in the forest than in the brains of the species that lives at the forests’ edges. Another brain structure that helps process sky light and polarized light is 23% larger in the deep forest species than in the forest edges species. Previous research has also shown that the deep forest species responds to lower intensities of light, and it makes sense that species of butterflies living in darker forests would need to be more sensitive to light to see and function in dimmer conditions.
The researchers think that these subtle differences in brain structures help keep the two butterfly lineages apart, contributing to their being two different species. It’s likely that the differences in brain structure impacts behavior such as foraging or mating, leading to divergent behaviors. Though these butterflies’ brains may not be as pretty as their wings, they’re just as fascinating.