Heliconius butterflies' mating preferences linked to a single gene

The vibrant wing patterns of tropical Heliconius butterflies, which serve both as a defense mechanism against predators due to their toxicity and as crucial cues in mate selection, have captivated scientists and nature enthusiasts alike. 

Experts have recently made significant advances in understanding the genetic basis of the mating preferences of Heliconius butterflies. The findings mark the first instance of a direct genetic link to visually guided behavior being identified in any animal species.

Behavioral experiments on Heliconius butterflies

The research was led by Richard Merrill, an evolutionary biologist at LMU Munich, alongside collaborators from the Universidad del Rosario in Bogotá, Colombia, and the Smithsonian Tropical Research Institute in Panama. 

During the course of their investigation, the team conducted extensive behavioral experiments on three Colombian Heliconius species: Heliconius melpomene and Heliconius timareta, both adorned with a bright red band on their forewings, along with Heliconius cydno, distinguished by a white band. 

Seeking mates with a similar appearance 

A fascinating discovery emerged: males of all species showed a predilection for mates that mirrored their own appearance, irrespective of the genetic distance between the two red-banded species.

By using genomic analyzes, the researchers identified a significant association with a specific region of the genome – a region where the red-banded species have exchanged genetic material due to hybridization. 

Key gene controls visual preference 

“We managed to identify regucalcin1 as a key gene controlling visual preference, in these butterflies,” said lead author Matteo Rossi, a researcher in Merrill’s lab. “If regucalcin1 is silenced, it impairs courtship toward conspecific females, proving a direct link between gene and behavior.”

This gene was found to have been transferred from H. melpomene to H. timareta in their evolutionary past, facilitating an increase in the attractiveness of red females and thereby enhancing the reproductive success of H. timareta. 

The role of hybridization in Heliconius butterflies 

“We’ve known for quite a while that the red color pattern gene was introduced from one species to the other through hybridization, and suspected that the same might be true for the corresponding preference. To finally show it, and identify the specific gene is really exciting,” said co-author Carolina Pardo-Diaz, the Dean of Biology at the Universidad del Rosario.

“We see differences in visual preferences all around us in nature when animals choose who to mate with. With our results, we were able to establish a direct link between a particular visual preference and a specific gene for the first time, and also demonstrate that hybridization can play an important role in the evolution of these behaviors,” added Merill. 

This study, published in the journal Science, not only advances our understanding of the genetic mechanisms underpinning mating behaviors in Heliconius butterflies but also highlights the role of hybridization in the evolution of such complex traits, offering new perspectives on the dynamic interplay between genetics and behavior in the natural world.

More about Heliconius butterflies

Heliconius butterflies, often known as passion vine butterflies, represent a fascinating and colorful group found primarily in tropical regions of South and Central America. 

These butterflies are especially known for their striking patterns and vibrant colors, which not only make them a subject of interest among scientists and butterfly enthusiasts but also play a crucial role in their survival.

Color patterns and mimicry

The wing patterns of Heliconius butterflies serve as a form of communication within their species and with their predators. Many species of Heliconius exhibit mimicry, where they share similar color patterns. 

This mimicry can be Müllerian, where poisonous species mimic each other’s warning signals to predators, enhancing their protection. Some Heliconius species also engage in Batesian mimicry, appearing like other toxic species to avoid predation, despite being harmless themselves.

Co-evolution with passion vine plants 

Heliconius butterflies have a unique relationship with passion vine plants, which serve as their primary food source during the larval stage. They lay their eggs on these plants, and the hatched larvae feed on the leaves, ingesting chemical compounds that make them distasteful to predators. 

This relationship is a classic example of co-evolution, where the butterflies and the plants have influenced each other’s evolutionary paths.

Unusually long lifespan 

Another intriguing aspect of Heliconius butterflies is their unusually long lifespan for insects, living up to several months. This is attributed to their ability to consume pollen in addition to nectar, a rare trait among butterflies. 

Pollen provides them with proteins and other nutrients, contributing to their longevity and ability to reproduce over extended periods.

Genetic exchange between species 

Research into Heliconius butterflies has also provided insights into genetics and evolution. Studies have shown how genetic exchange between species through hybridization can lead to the transfer of beneficial traits, such as wing color patterns, which play a vital role in their survival and reproductive success.

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