Up to 20 layers of transparent scales on butterfly wings scatter white light to produce brilliant blue structural color. Alison Sweeney, Duke University, and collaborators at the Smithsonian Tropical Research Institute report in Nature that polarized light from iridescent female Heliconius butterflies functions as a mating signal. This may be the first example of mate recognition based on polarized light. Physical properties of wing scales may play an important role in speciation of Heliconius butterflies.
People in small planes flying low over tropical forest often comment about the tiny flashes of blue from iridescent butterfly wings that stand out against dark green jungle foliage. But the ecological significance of light scattering and shaping by butterflies has, for the most part, been overlooked.
Sweeney brings a new emphasis on the physical properties of butterfly wings to a group studying the genetics and ecology of speciation in Heliconius butterflies. She presented moving female butterfly wings to conspecific males with and without filters that eliminate polarized light. Males of an iridescent species approached females producing polarized signals significantly more often when signals were not depolarized. Males of another, non-iridescent species approached females, which do not produce polarized signals, at the same rate regardless of the presence or absence of the depolarizing filters.
Differences in light bending by genetically inherited patterns of butterfly scales may be important in sexual selection and speciation of Heliconius butterflies and may vary according to the specific light environment they occupy in tropical forests.
Ref. Alison Sweeney, Christopher Jiggins, Sonke Johnsen. Polarized light as a butterfly mating signal. Nature. 1 May, 2003.
The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is one of the world´s leading centers for research on the ecology, evolution and conservation of tropical organisms.
The above story is based on materials provided by Smithsonian Institution. Note: Materials may be edited for content and length.
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