A high magnification image of a Heliconius erato wing highlights the mosaic of monochromatic scales that comprise the wing pattern. These wing patterns serve as 'stop signs' for would-be predators, delivering the message “Don’t eat me, I taste bad.” Reed et al. determine that the gene, optix, drives the evolution of red warning coloration across the genus Heliconius, therefore allowing these butterflies to participate in numerous color pattern mimicry complexes throughout the neotropics.
Credit: Arnaud Martin
Heliconius erato petiverana in Panama display their warning colouration while roosting for the night.
Credit: Chris Jiggins
SHROPSHIRE: Scientists have discovered how copycat behaviour has evolved in certain butterfly species, helping to protect them from predators.
Over millions of years, the wing patterns of these butterflies have evolved to resemble one another, a phenomenon that a new study published in Science has shown to be driven by a solitary gene.
"The fact that a single gene can produce the incredible diversity of complex wing patterns we see in nature is stunning," said lead author Robert Reed from the University of California, US. "[The gene] controls a whole array of highly detailed wing patterns which can look totally different from species to species and from region to region."
Copycat creatures
Fans of the Harry Potter books may remember that in the final book, Potter's allies used Polyjuice Potion to transform themselves into Potter clones to escape Lord Voldemort and his cronies and allow Potter to flee to safety.
A cunning ploy indeed, and one that also has parallels in the natural world. Certain species can evolve to imitate another species - known as mimicry - as a defence mechanism against predators.
Mimicry works because many creatures possess warning signals. These signals, which may take the form of colours, sounds or odours, are used to deter a potential predator by delivering the message, “Don’t eat me, I taste bad.”
One of the most common forms of mimicry sees two or more species sharing a similar warning signal. Known as 'Müllerian mimicry', it is beneficial for all species involved because a predator only needs to be exposed to one species in order for it to avoid all of them. In other words, a kind of mutual agreement has evolved between the prey species.
Butterfly mimicry
Müllerian mimicry is especially common in Heliconius butterflies, also known as passion vine butterflies. These colourful insects, found mostly in Central and South America, boast bright, reddish wing patterns that are often remarkably similar.
There are around 40 species of Heliconius butterflies, almost all of which are thought to participate in mimicry. Until now, however, little was known about the genes that govern this behaviour.
For more than a decade, Reed and colleagues studied Heliconius butterflies in order to understand the evolution of their wing patterns.
A solitary gene
The researchers made their discovery by identifying part of the genome of a Heliconius butterfly species. They were then able to probe this DNA sequence with genetic information from microscopic pieces of Heliconius butterfly wings, in order to look for matches.
Their experiment showed that a gene called optix was the only one consistently associated with the red wing patterns. This result was confirmed by studying the DNA variations in natural populations of Heliconius butterflies. Although it is remarkable that a single gene drives the evolution of these complex butterfly wing patterns, it is not yet understood how optix can control so many different colour pattern elements.
Evolutionary enigmas
This work has broader implications for evolutionary theory, according to Camilo Salazar, a member of the Butterfly Genetics Group at Cambridge University, UK.
"In evolutionary biology we are interested in answering questions such as 'what is the genetic basis of adaptation?' and 'how many genes are involved in producing adaptive traits?' said Salazar. "With this study, the authors began to answer these questions for one of the best examples of natural selection - mimicry - helping us to understand how the biological diversity observed in our world is produced."
Reed added, "Out of the tens of thousands of genes in a given genome, why do there only seem to be a few that consistently drive rapid evolutionary change? This is one of the big questions emerging in modern evolutionary biology."
