Army Ants Unchanged Since The Cretaceous

[Richard W Travsky <rtravsky@uwyo.edu>]

I have this image in mind now of a large dinosaur rolling on the
ground to scratch its back...


http://news.bbc.co.uk/1/hi/sci/tech/3014011.stm

Army ants, these days dispersed across the world, all came from a single
source over 100 million years ago on the ancient supercontinent of
Gondwana.

A new study indicates the insects all share identical genetic markers that
reveal a common ancestor.

Many scientists believed that army ants originated separately on several
continents relatively recently in Earth history.

But the new research means that army ants join animals such as sharks and
crocodiles that have remained relatively unchanged for many tens of
millions of years. 
...
Because army ants are found almost everywhere, scientists postulated that
they evolved many times after the break-up and dispersal of the
supercontinent Gondwana just over 100 million years ago.

The conventional view of the evolution of army ants needs a revision
because of new data obtained by Sean Brady, a Cornell University, US,
entomologist who has discovered that these ants evolved from a common
ancestor.

"Biologists have wondered why army ants, whose queens can't fly or get
caught up by the wind, are so similar all around the world," he says.

The answer is that "army ants have evolved only once and that was in the
mid-Cretaceous period". 

Brady studied the DNA of 30 army ant species and 20 possible ancestors
within the ant community, looking specifically for genetic clues to their
relationships.

"Essentially, I built a genetic family tree. Then I took that family tree
and looked at its genetic tree rings to postulate what happened in the
past," he says.

Combining the genetic data with fossil information, Brady found that all
the species share the same genetic mutations.

"If they share those mutations, we can infer they evolved from the same
source," Brady says.

His research is published in the Proceedings of the National Academy of
Science (PNAS) journal.