Life in the forest’s understory versus its canopy changes flight among closely related butterflies

Brightly colored and iconic Morpho butterflies of the Amazon have evolved a complex collection of adaptive aerodynamic and behavioral traits that allow them to navigate their tropical forest habitats. In a new study, researchers show how natural selection imposed by different microhabitats across forest strata can drive codivergent evolution of wing shape and flight behavior among such closely related species. Flying insects like butterflies exhibit a diversity of flight patterns and aerodynamic mechanisms reflecting unique habitats and lifestyles. Investigating how these creatures fly is central to understanding how natural selection shapes flight. However, while insect flight has been studied in detail in several species, the evolution of flight among closely related species adapted to different habitats isn’t well understood. Using high-speed videography on freely flying butterflies, as well as morphometric analyses and aerodynamic modeling, Camille Le Roy and colleagues investigated the codivergence in wing shape, aerodynamic efficiency, and “flap-gliding” flight behavior among 12 different Morpho species living in different forest strata. Le Roy et al. discovered that these species have evolved a diverse set of morphological and behavioral patterns that differ depending on whether they live in the forest’s understory or canopy. Those that evolved to occupy cluttered understory habitat display more powerful wing-flapping phases, resulting in fast and agile flight. On the other hand, Morpho butterflies that adapted to open canopy habitats evolved improved and efficient gliding abilities, thanks to unique combinations of flight behavior, wing shape, and other aerodynamic mechanisms. These traits varied even across canopy-dwelling species, suggesting multiple pathways of adaptive evolution that led to colonizing this part of the forest.