Butterflies come in an incredible array of shapes and colors, from the bright blue morphos to the iconic monarchs. It now turns out that the different genetic components that give rise to these color patterns can be shared between species when they interbreed and form new patterns not seen before, kind of like a “genetic paint-box.”
While the notion of species interbreeding and sharing genetic material is not new, this study is the first to show that this swapping of genes can give rise to entirely new patterns, by creating a novel mix of gene expression patterns. They found that each pattern variation had its own genetic switch, and it was these switches that were controlling what coloration is then seen.
The researchers were looking at two of the most common wing patterns found in a multitude of different combinations on Heliconius butterflies. Many of the brightly colored insects, distributed widely from the Amazon rainforest to the southern U.S., display a red patch on the forewing, and a red ray burst on the hindwing. What they found was that these two characteristics actually came from two separate species of butterfly, which they think originally interbred around 2 million years ago. Since then, the genetic material that codes for these patterns has been swapped and traded, forming an array of different wing patterns.
The two patterns, they discovered, have two separate switches that can be turned either on or off, despite the sections of DNA that code for the patterns being sat right next to each other in the genome. “By identifying the genetic switches associated with bits of wing pattern, when they evolved and how they diverged, we can actually map onto the species tree how these little regions of colour have jumped between species – and we can see they are jumping about all over the place,” explains Professor Chris Jiggins, who coauthored the paper published in PLOS Biology.
Heliconius butterfly showing both the patches on the forewing, and the ray burst on the hindwing. Jiggins group, Cambridge
The researchers liken this ability to share the genes, and, more importantly, the switches that control them, to a “genetic paint-box.” They explain that while the portion of DNA that codes for the pattern cannot be altered as it is also involved in other aspects of the butterflies’ biology, it is the switches that are independent, and as these are shared and tinkered with, the patterning on the wing is then altered.
It is thought that this new understanding of how color variations can be shared and shuffled between butterflies could give new insights into the insects' rapid diversification, which can occur even within just a single generation.
Top image in text: Evolutionary tree showing the relationships between the different species of Heliconius butterflies, and their color patterns. Jiggins group, Cambridge.