Butterfly wings are known for their dazzling palettes, but they are also the canvases that display complex behavioral signals. Among Heliconius cydno butterflies in Central and South America, males choose females to court as potential mates largely based on whether their wings are white or yellow. But how deep do these preferences go?
In a new paper published in PLOS Biology, scientists at the University of Chicago reveal how simple genetic tweaks and changes in the visual system can reshape butterfly perception and partiality, unraveling how beauty — and the preferences that define it — can influence the course of evolution.
“The mystery we’re trying to explore ultimately comes down to the question of what makes something beautiful or attractive,” said co-senior author Marcus Kronforst, PhD, Professor of Ecology and Evolution. “It helps us understand where biological diversity comes from, because aesthetic preferences can contribute to one species splitting into multiple species.”
“Digging down into the mechanisms of preference evolution opens up new avenues for future theories and models of how evolution ‘works’ as a whole,” added co-senior author Stephanie Palmer, PhD, Associate Professor in both Physics and Organismal Biology and Anatomy.
Multidisciplinary butterfly investigation
Heliconius butterflies, which the Kronforst Lab has studied for years, are known for bold wing patterns that warn predators of their toxicity — a clever survival tactic. But scientists discovered that these same wing colors take on a second job: fueling visual mating cues. While a toxic predator deterrent might not sound romantic, male butterflies in certain populations appear to strongly prefer females that match their own color: white or yellow.
“These butterflies have the colors they like deeply engrained in their `hearts and souls,’” said Palmer. “It’s like specialized rose-colored glasses come for free with their wing patterns and make their ideal mates look better.”
To investigate how and why the males so uniformly prefer to match with females who…well…match them, the Kronforst and Palmer labs teamed up to simultaneously dive into the butterflies’ genomes, eyes and brains.
“We wanted to tackle the question from every angle,” said Kronforst.
Surprisingly simple answers
It turns out these complex mating behaviors boil down to a few simple factors.
Using both genomic and transcriptomic approaches, the Kronforst team discovered that the strongest signals linking genes to mate choice cluster near a single chromosomal region (called the K locus) that also controls whether a butterfly’s wings are white or yellow. By examining which genes activate at different stages in the butterflies’ development, the team found seven candidate genes in this region that are active in the eyes or brain in ways that differ between white-winged and yellow-winged males. Many of these genes influence how nerve cells form or connect to each other, hinting that these genes might help “wire” the butterflies’ visual systems differently based on wing color.
“A key takeaway is that small changes in the ways organisms sense their environment can potentially lead to big changes in their behavior,” said co-first author Nicholas VanKuren, PhD, a postdoctoral researcher in the Kronforst Lab who led the genetics experiments. “So, it shouldn’t be surprising when organisms — including people — vary widely in their preferences.”
On the neurobiology side, co-first author Nathan Buerkle, a graduate student in the Palmer Lab, undertook the incredibly “fiddly” task of inserting superfine microelectrodes into individual receptors in butterflies’ eyes to measure their response to different wavelengths of light. They discovered that in yellow males, visual receptors that are sensitive to ultraviolet (UV) light receive inhibitory signals from neighboring cells that detect other light wavelengths. This extra step of “damping down” UV responses may be crucial for perceiving females with yellow wings (which reflect less UV light) as attractive. Meanwhile, males that favor white wings have a different sensory wiring pattern, making them attuned to the strong UV reflectance of white scales. Notably, white and yellow females did not show these differences in wiring, indicating that it really is specific to the males’ role of initiating courtship based on wing patterns.
“Now that we’ve found these key pieces at the different levels of genetics and neurobiology, our future research can hopefully connect those pieces together like Lego bricks,” Kronforst said.
Implications bigger than butterflies
Although these specific genetic and neurobiological differences only apply to these butterflies, the researchers say the project helps them understand the phenomenon of preference more broadly. The forces causing one butterfly to choose another might be related to those that cause a bird to choose one seed over the other or a person to prefer blue clothes over green.
“We can learn something from these little bugs about how preferences evolve,” VanKuren said.
Kronforst pointed out that although humans like to think they make purely conscious, intentional decisions about who to love, marry and mate with, there’s evidence that those choices are also influenced by subconscious assessments about potential mates through sensing pheromones.
“Similarly, these little butterflies are flying around, thinking they love each other, but really they're assessing colors filtered through differential wires in the eye, and that's how these decisions are being made,” Kronforst said.
Of course, those “differential wires” could be just the tip of the iceberg, raising the possibility that many animals — perhaps even humans — can tune their sensory systems in subtle ways that affect everything from mate choice to everyday preferences.
“Invertebrates seem willing to muck about with their external sensors that affect how they see the world, which originally seemed bonkers to me. But you can change things really quickly if you just change your filters on the external world,” Palmer said. “Who knows? Maybe we as humans do some of that too. It makes you want to reflect on why you have the choices and preferences you have.”
“Genetic, developmental and neural changes underlying the evolution of butterfly mate preference” was published in PLOS Biology in March 2025. Authors include: Nicholas VanKuren, Nathan Buerkle, Wei Lu, Erica Westerman, Alexandria Im, Darli Massardo, Laura Southcott, Stephanie Palmer and Marcus Kronforst.
