A unique and curious new species of Dracula ants - so-called
because they feed on the blood of their young - has been discovered
in the rotting leaf litter of a Madagascar forest, and scientists
say it will force them to rethink the entire path of ant
evolution.
To entomologist Brian Fisher, who discovered the insects, the find
may well prove as significant for the insect world as discoveries
of humanity's fossil ancestors in Africa, which offered new
insights into human evolution.
His find, Fisher says, could offer a crucial key to understanding
how ants have evolved and diversified from their ancestors, the
wasps, tens of millions of years ago.
Fisher, the assistant curator of entomology at the California
Academy of Sciences in San Francisco, has spent five years in
Madagascar searching for ants, including the new species, unique
members of the ant genus Adetomyrma.
Ant study can be a risky business at best. In the course of his
many years hunting ants throughout Africa and Madagascar, Fisher
has suffered just about every tropical disease. "They've used
medicines on me that you can't even find in America," he
said.
Slender, bearded and filled with excitement, Fisher the hunter has
already discovered 600 new ant species in Madagascar - all new to
science, and 74 of which are members of the genus
Strumagenys.
Only weeks ago, Fisher plunged his scarred arm into a rotten log
and uncovered the first colony of red-orange Dracula ants, complete
with their yellow queen and white larvae. He recognized instantly
that they were different from all the other species he had
discovered.
"There they were, crawling over me and stinging my hand, and I was
crazy with excitement and joy," he said. "I was, like, 'oh my gosh,
are these what I think they are?' The driving force for all of us
in science is the thrill of discovery, and here was my biggest
thrill of all right there."
Madagascar, an island off the coast of East Africa, is one of the
world's centers of unique biodiversity. It split from Africa some
180 million years ago, and its isolation has enabled scores of
plants and animals to evolve into new species.
Only in recent years has Madagascar become prey to forces of
development. Its plant and animal life - including the primitive
primates called lemurs - are threatened as never before: The human
population is soaring, native trees are being harvested and roads
are carving up the landscape.
But the ants are still there, although as Fisher laments, "They are
relics of the earliest days of evolution, and if we don't collect
some to study now, in another 10 years they'll be gone."
The new species has unique characteristics. They are the only ants
that have a rear third of the body, called the gaster, connected
directly to the middle section, called the thorax. That connection
is almost identical to the bodies of wasps, from whom these ants
are believed to have descended some 70 to 80 million years
ago.
In all other ants, Fisher explained, a series of slender,
constricted segments link the gaster and thorax. That segmented
waist endows them with greater flexibility - perhaps to escape from
predators in tight spaces. The new Madagascar species, with far
fewer natural predators, may never have needed to evolve a more
flexible body.
While most ants are noted for their "social food transfer"
behavior, in which the workers share solid food with each other and
carry it to the solitary queen in each colony, members of Fisher's
new species are, as he puts it, "nondestructive cannibals."
To humans, they would seem savages indeed. Like vampires, the
workers must prey on the larvae in their own nursery, scratching
the skin of the larvae until they bleed, then chewing on the young,
gorging on the blood and regurgitating the blood to feed the
sedentary, wingless queens.
"The larvae aren't killed," Fisher said, "but when you look at them
closely in the colony, you can see that they're all scarred."
Both in their vampire-like social behavior and their thickened
bodies, Fisher's ants seem to lie somewhere between more primitive
ants and their ancestral wasps on one side, and more recently
evolved ants on the other.
In 1993, Philip Ward, an entomologist at the University of
California at Davis, was exploring in Madagascar and found a
cluster of worker ants that also bore the unique body shape Fisher
found a month ago. But he could go no further in his research
because he found no larvae, no males and no queen. He simply called
them "enigmatic" in a scientific journal report he published.
Now the enigma is ever more puzzling, Ward said yesterday: The
species' behavior and body structure "continues the mystery of ant
evolution," he said. The new species, he said, shows how remarkably
specialized their behavior has become - "a strange mixture of the
primitive and the derived," he called it.
Ant species are currently divided into two sub-families, and the
Adetomyrma somehow share characteristics of both groups, so the
distinctions between them are unclear - another indication that the
entire ant evolutionary tree may need to be redrawn, Fisher
said.
"The big question is, what has led to this amazingly successful
development in evolution? It's so important because it will help us
reconstruct the ancestral character of all the ants, and it will
require us to rethink the entire process of ant evolution."
http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2001/01/15/MN138629.DTL
