January 25, 2008

Ants’ Infected Red Rumps Look Yummy

stomach flus may be gut-wrenching for us, but consider the plight of some
tropical black ants: When infected by tiny nematode worms, the ants' rumps
resemble a bright-red, bird-attracting berry.

parasites' strange transformative ability might help it spread to other ant
colonies, scientists report in two new studies. Birds normally avoid eating
the foul-tasting ants, but the berry-like temptation may be too much, said
researcher Steve Yanoviak, an insect ecologist at the University of Arkansas in Little Rock.

ants are strange. Half of the solid material they bring into their nests is
bird poop, which they feed to their larvae," Yanoviak said of the ant
specie, Cephalotes atratus.
"That sets the stage for an easy, consistent way for the nematodes to get
into a colony."

and his colleagues detail the ant-parasite relationship in an upcoming issue of
the journal American Naturalist and describe the new species of nematode
parasite — Myrmeconema neotropicum — in an upcoming edition of the
journal Systematic Parasitology.


When ants
lug infected bird doo-doo is lugged into their colony and feed to helpless
larvae, Yanoviak said, the parasite migrates into their abdomens, or gasters.

settled into the pencil-eraser-sized gaster, the worms partially dissolve the
insect's jet-black exoskeleton to make it translucent.

you combine that with the amber color of the eggs and shine sunlight on it, you
get something that looks remarkably like a berry," Yanoviak told LiveScience,
noting that the infestation also causes the ant's rear to stick up in the air.
"We think birds confuse [the gaster] for local varieties of berries,
completing the parasite's life cycle."

infestation might sound horrific, but Yanoviak said he isn't sure it reduces
ant lifespan all that much.

cut open a lot of these ants and their digestive tracts are still in
tact," Yanoviak said, comparing the infection to a wild case of tapeworms
in humans. "The nutrition goes directly to the parasites, which makes for
a scrawny ant, but I've tracked ants that lived for at least 3 months."

unaffected by the parasite live for about 6 months, he said.

Berry bum evolution

thinks the parasite evolved as a result of the unique relationship between
tropical birds and their dung-recycling ants, which are also known for their mid-air
gliding ability

see similar parasites in fire ants and beetles from other regions, but they
don't cause the red discoloration," Yanoviak said. "All the pieces
seem to be in place for this parasite to evolve the way it did."

explained that birds tend to carry a lot of parasites, and that the ants tend
to collect bird droppings during the day. Over time, he noted, the parasite
exploited the unoccupied ecological niche.

almost no end to the amazing things that parasites can do," Yanoviak said,
"no matter how simple they are."