Scientists have found that some passion vine butterflies (Heliconius) share similar color patterns that help ward off predators because they actually share parts of their DNA as a result of hybridization somewhere in their ancestry.
But a new study in Science provides evidence that the process of sharing DNA may be far more common than ever thought, offering a potential clue to how biodiversity took place.
An analysis of 20 butterfly genomes found evidence that many butterfly species — including distantly related ones — show a surprisingly high amount of gene flow between them, said James Mallet, professor of organismic and evolutionary biology in residence and associate of population genetics in the Museum of Comparative Zoology, the senior author of the study.
“DNA sharing had been shown in closely related species, but we wanted to probe deeper into the phylogenetic tree,” Mallet said. “What we found is really astonishing: introgression even among species that are distantly related. ‘Species’ are simply not what we thought they were, and now we have the data to show it. The evolutionary tree of butterflies is a complete morass of interconnectedness.”
For Mallet and colleagues, understanding how butterflies pass genes back and forth — a process known as introgression — began with the creation of 20 new “genome assemblies” of various species in the Heliconius family.
Those assemblies, explained Nate Edelman, lead author on the paper and a graduate student in the Mallet lab, essentially function as genomic maps, and are constructed by sequencing short fragments of DNA and then assembling them in the proper order.
Once created, those maps can also serve as important resources for future researchers, allowing them to map genes back to the genome.
“The cool thing about making genome assemblies instead of simple genome “resequencing” is that it’s not just the DNA bases that change — the entire structure of genomes can change through evolutionary time,” Edelman said. “And using the assemblies, we can detect those changes.”
When they began analyzing the assemblies, Mallet said, the team not only found evidence that some genes were capable of moving between species, but that others were far more resistant to the process.
And one of the key factors determining whether genes could or could not move is a basic biological process called recombination.