They
look like characters that belong in the Marvel Comic The Hulk, whose
body reacts to stress by expanding in size. With huge oblong heads and
giant, vicious mandibles, these are supersoldiers of the hyperdiverse
ant genus Pheidole. Normally, these supersoldiers occur naturally only
in limited geographical regions. But now researchers, led by McGill
biology professor Ehab Abouheif, have found ants that are biological
anomalies with supersoldier-like characteristics in unexpected regions.
And, more importantly, researchers have discovered they can induce
supersoldiers in Pheidole ant species that never had them before.
These supersoldier anomalies represent dormant ancestral potential that
can be invoked by changes in the environment. They represent, in effect,
a source of raw material for natural selection to act upon. The finding,
published in the most recent edition of Science, is a significant
advance in our understanding of evolutionary processes.
“Birds with teeth, snakes with fingers, and humans with ape-like hair –
these are ancestral traits that pop up regularly in nature,” Abouheif
explains. “But for the longest time in evolutionary theory, these
ancestral traits were thought to go nowhere – slips in the developmental
system that reveal things from the past, the Barnum and Bailey of
evolution. So they’ve been an unappreciated source of evolutionary
variation.”
In Pheidole (big-headed) ant colonies, there are millions of individual
workers, including minor workers and soldiers. Typically, depending on
the food the ants are fed, certain hormones are triggered in the ant
larvae and they either develop into soldiers or minor workers. After
unexpectedly finding supersoldier-like anomalies in Pheidole species in
Long Island, where they aren’t normally seen, Abouheif and his team knew
something unusual was going on. “I’ve been collecting samples there for
almost 15 years,” said Abouheif. “But when I saw them, I thought, ‘Holy
cow! Those are monstrous looking soldiers!’ They look like the ones that
are naturally produced in the American southwest.”
So
researchers in Abouheif's lab led by PhD student Rajee Rajakumar and
collaborators at the University of Arizona then started trying to
artificially induce the production of these supersoldiers. They did so
by applying juvenile hormone to the ant larvae at critical stages in
their development. And met with immediate success. They were able to
produce supersoldier subcastes in at least three species in the genus
where they have never been seen before – species that are widely
separated in the evolutionary tree of Pheidole.
These findings are groundbreaking for evolutionary theory, according to
Abouheif, because they show there is dormant genetic potential that can
be locked in place for a very long time. “The kind of environmental
stressors that evoke this dormant potential are there all the time – so
when the need arises natural selection can take hold of the potential
and actualize it,” Abouheif explained. “So what we’re showing is that
environmental stress is important for evolution because it can
facilitate the development of novel phenotypes. Anytime you have a
mismatch between the normal environment of the organism and its genetic
potential you can release them – and these things can be locked in place
for 30-65 million years.”
The research was funded by Natural Sciences and Engineering Research
Council of Canada, the Canada Research Chair in Evolutionary Development
Biology, the National Sciences Foundation, Konrad Lorenz Institute
Fellowship.
