Butterfly mate preferences shift with slight brain changes

Nature is always changing, sometimes in small but powerful ways. Genetic and brain changes can shape how species behave. A recent study by Nicholas VanKuren and Nathan Buerkle at the University of Chicago reveals how a simple neural change can shift mating preferences in male butterflies.

The findings show that small brain and sensory changes can quickly alter behavior, helping species evolve.

Butterfly survival and mate selection

Heliconius butterflies, known for their striking wing patterns and colors, use these visual signals as a defense against predators. Their bright hues serve as warnings, signaling toxicity or unpalatability.

Since survival depends on these warning signals, males have evolved a strong preference for females with similar wing colors. Choosing mates with matching patterns ensures that future generations retain these critical survival traits.

Despite the clear evolutionary advantages of such preferences, little is known about the underlying genetic and neurological mechanisms. What makes a male butterfly prefer a female with a particular wing color?

Scientists aimed to uncover the sensory and genetic factors influencing these choices by studying two subspecies of Heliconius cydno, one with yellow patches on its wings and the other with white.

The research has revealed the deep connections between vision, genetics, and behavior in shaping mate selection.

Butterfly mate choice and genetics

To understand the genetic basis of mate preference, the researchers examined the genomes of the butterflies.

They identified four specific genomic regions linked to both wing color and mate selection. One of these, known as the “K locus,” had already been associated with similar traits in other Heliconius butterflies.

This finding suggests a common genetic mechanism influencing both physical traits and behavioral tendencies in these insects.

The team also explored gene expression patterns in different parts of the butterfly’s nervous system, including the retina, optic lobe, and brain.

The researchers found that seven genetic variants were not only located in regions associated with mate preference but were also expressed at different levels in yellow and white males. These variations likely play a direct role in determining which wing color a male butterfly finds attractive.

Butterfly vision affects mate choices

Beyond genetic factors, the researchers investigated how these butterflies process visual information.

They focused on the activity of photoreceptors in the butterflies’ eyes, which play a crucial role in distinguishing colors. Their experiments revealed a striking difference in how color perception influences mate preference.

Male butterflies that preferred yellow-winged females had green-sensitive photoreceptors that strongly inhibited the activity of UV-sensitive photoreceptors. This inhibition was significantly weaker in males that did not show the same preference.

This means that a relatively simple modification in the peripheral nervous system alters how butterflies perceive different wing colors, shaping their mate choices.

The findings suggest that mating preferences are not just about detecting certain colors but rather about how the brain processes sensory information. Males are not simply seeing a preferred color more clearly; their nervous systems are wired to find one wing color more attractive than another.

Evolutionary implications of sensory changes

The ability to rapidly alter sensory processing could be a key driver of behavioral evolution in butterflies.

Since inhibitory relationships between photoreceptors can evolve quickly, changes in mating preferences may emerge in relatively short periods. This flexibility allows populations to adapt to new environmental conditions and evolve distinct mating behaviors.

The study provides valuable insight into how such changes can drive species evolution. “Inhibitory relationships between photoreceptors are easily evolvable, which may allow rapid behavioral evolution,” noted the researchers.

By altering how butterflies perceive potential mates, these neural modifications can contribute to reproductive isolation, eventually leading to the formation of new species.

Mate choice mechanisms

Understanding the genetic and neurological basis of mate preference in butterflies extends beyond this single species.

Similar mechanisms may exist in other animals where visual cues play a central role in mating decisions. By identifying the genetic and neural pathways that shape attraction, scientists can gain deeper insights into the broader forces driving evolutionary change.

The study paints a comprehensive picture of how small genetic differences influence sensory processing, which in turn affects behavior.

“Our work generated a striking picture of how a critical visual behavior – mate choice – is controlled, from variation in the connections between neurons in the eye down to genetic variation across the genome,” concluded the researchers.

The study is published in the journal PLOS Biology.

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