November 7, 2017
Female swallowtail butterflies do something a
lot of butterflies do to survive: they mimic wing patterns, shapes and colors
of other species that are toxic to predators. Some - but not all - swallowtail
species have evolved several different forms of this trait. But what kind of
genetic changes led to these various disguises, and why would some species
maintain an undisguised form when mimicry provides an obvious evolutionary
advantage?
In a new study published this week
in Nature Communications, scientists from the University of Chicago
analyze genetic data from a group of swallowtail species to find out when and
how mimicry first evolved, and what has been driving those changes since then.
It's a story that started around two million years ago, but instead of steady,
progressive changes, one chance genetic switch helped create the first
swallowtail mimics. And it has stuck around ever since.
"In butterflies with one color pattern,
we have a gene in a normal orientation on the chromosome. In the butterflies
with the unusual, alternate color pattern, that gene was spliced out, flipped,
and then spliced back into the chromosome at some point," said Marcus
Kronforst, PhD, associate professor of ecology and evolution at UChicago and
the senior author of the study.
"That flip, or inversion, keeps the
two genes from recombining
if those two different kinds of butterflies mate, so they've kept both copies
of the gene over evolutionary time, since they split from their common ancestor
two million years ago," Kronforst said.
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