Butterfly genomes show surprising evolutionary history


These two butterflies, even though they
look very similar, are actually from different species. And in fact if you
move down the line here this is actually one species with different color morphs
and this is a separate species with the same color morphs. And so as you can see some members of each species resemble a different species more closely than they
do members of their own species. So while historically we’ve always
thought of the evolutionary process as tree-like, It turns out that, when you
start to dig into the genomes, it’s a lot more complicated than that. One of the
really cool things about our study is that we sequenced 20 new genomes.
Previously there had only been about two high-quality reference genomes and with
those genomes, we were able to get an unprecedented high-resolution look at
their evolutionary history. Many evolutionary biologists think that
there’s not very much genetic exchange after speciation. However many believe
that there is genetic exchange and we came up with a new method that
discriminates between those two opposing views. And so with 20 whole genomes the
first thing that we had to do was line them up so we could see which portions
of the genome shared an evolutionary history. And in the case of Heliconius
butterflies, each specimen has about 250 to 300 million different units of DNA.
And so using that entire dataset, which is truly big data, and new methods and
big computers like we have at BYU and that Harvard has, we found that the
evolutionary history of this species involves a lot of genetic exchange after
things become distinct species. And it’s been particularly noticed at genes that
control for their color patterns and that allows them to become a more
effective mimic. The reason they look similar to each other is they’re both
toxic and so by mimicking each other they can let predators know not to come
and eat them. There’s a whole science involved in generating evolutionary
trees. This is basically a map that shows a series of bifurcations, meaning that
the species split and split again. However what we found in this study is
that rather than resembling a tree, the evolutionary history resembles more of a
bush. There’s genetic information being transferred horizontally.
We hope that other people who are studying different groups of animals
will start to look for these same types of evolutionary signatures to understand
whether this is a really important evolutionary process among all of life. Not only does the study give us a really good understanding of the evolutionary
history of this particular group of butterflies, these methods that we used
with multiple whole genome assemblies, set a nice template for other people to
go out and study other organisms.

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