In order to continue its lifecycle, a newly discovered parasitic nematode takes advantage of a species of ant dubbed Cephalotes atratus. As researchers explain in an upcoming issue of The American Naturalist, this particular nematode does not visibly infect C. atratus like most other parasites. Instead, it changes both the ant’s appearance and behaviour. After infection, the ant’s abdomen transforms to look like a bright red, ripe, juicy berry. It is believed that this physical change tricks birds into believing the infected ants are fruit—and eating them. As the ant changes its mannerisms and goes into an alarm stance, it raises its abdomen in the air, making it an easier target for predators. The birds eat the infected ants and excrete the parasitic nematode eggs in their feces. Other ants collect the parasitecontaminated bird feces and then feed it to their larvae. The young ants’ abdomens then fill up with parasite eggs, continuing the nematodes’ life cycle.
Interestingly, the distinct colouration of the ant’s abdomen is not caused by pigment.
“The gaster [infected ant abdomen] does not actually take on a red pigment,” said Stephen P. Yanoviak to Discovery News. Yanoviak is a coauthor of the study and assistant professor of biology at the University of Arkansas at Little Rock.
“Instead it becomes translucent amber. With the yellowish [parasite] eggs inside and a touch of sunlight, it appears bright red,” he said.
While the mechanism behind how the parasites change an ant’s abdomen is still undetermined, researchers have some ideas.
“We think the worms either sequester pigment compounds from the exoskeleton or they make the exoskeleton thinner—or maybe both,” Yanoviak said.
In May 2005, Yanoviak was studying the gliding ability of C. atratus with colleagues Robert Dudley, a professor of integrative biology at the University of California at Berkeley, and Michael E. Kaspari, an ant ecologist at the University of Oklahoma in Norman. By chance, Dudley happened upon the infected ants. Their unusual appearance perplexed all three scientists, but they did not all agree on how it could occur.
“Like other ant biologists, I initially thought this was another species of Cephalotes,” said Kaspari. “Robert didn’t think so, and we made a bet over beers. Then Steve opened one up under the scope and—wow! I lost the bet.”
Upon dissecting the ants in the lab, Yanoviak found that hundreds of nematode eggs were packed into the ants’ abdomens.
The discovery is the first described example of parasite-induced fruit mimicry.
“It’s just crazy that something as dumb as a nematode can manipulate its host’s exterior morphology and behaviour in ways sufficient to convince a clever bird to facilitate transmission of the nematode,” Dudley said.
