More than a million animals on the planet are presumed to use color vision to find food, to find mates and to avoid being eaten by predators. This is because color information is more reliable than other kinds of visual cues like an object's brightness. Despite the widespread use of color by animals to advertise to potential mates and to warn predators against attack, scientists know very little about the way color vision works in most organisms, including why color vision differs between males and females in some species. This project aims to examine vision in a group of toxic butterflies that display a new form of coloration on their wings, ultraviolet-yellow, and have novel violet and ultraviolet photoreceptors in their eyes. This project will identify key parts of their genome which control eye development and the placement of photoreceptors in their eyes, which differ between the sexes. The differences in ability between males and females to detect color will be studied using behavioral tests and linked to cues in the butterflies' light environment which contribute to their survival and reproduction. In addition, this project will result in the training of the next generation of scholars - graduate and postdoctoral students in physiological methods, which will permit the recording of an animal's response to light. Undergraduates will be trained in the annotation of genomes. Lastly, the project will make freely-available a method for increasing the production of difficult-to-study light-sensitive proteins, which may be useful for a variety of biotechnology applications.
Mimetic animal coloration evolves in the context of predator confusion. Unless mimetic animals have adaptations for discriminating between mimetic colors there is a risk of confusion for the animals themselves, with negative consequences for mating and reproduction. Heliconius butterflies are of interest because many unpalatable species have formed mimicry rings in the Neotropics. The research team has discovered that Heliconius eyes express duplicated ultraviolet (UV) opsins and have shown that this duplication may be an adaptation for species recognition, via enhanced UV color vision. The proposed project will permit the elucidation of the biological significance of the ultraviolet opsin duplication by tracing species- and sex-specific patterns of photoreceptor evolution using immunohistochemistry, character mapping, and ancestral state reconstruction. In addition the project will draw on a Heliconius butterfly reference genome together with other genomic resources and transcriptomic resources that the project will generate, to identify eye genes that may have been the target of selection in these different lineages along with the duplicate UV opsin gene. The proposed work will reveal in unprecedented detail the evolution of color vision within a group of closely-related butterflies in relation to the signals they encounter in their daily lives. Whereas there has been much work on sexual dimorphism in signals, there is virtually no work on sexual dimorphism in sensory systems especially in color vision. This is a major gap that we can now begin to fill using a variety of methods: Pac-Bio and Illumina DNA-sequencing, ATAC-seq, RNA-seq, intracellular electrophysiology, cell culture, and behavioral tests.
