Jennifer Viegas, Discovery News
Jan. 17, 2008 -- To perpetuate its life cycle, a newly identified parasite morphs its ant victims to such a degree that the infected ants resemble red, ripe juicy berries that birds are more inclined to pick, according to the University of California at Berkeley.
Eggs from the parasite then pass through the unwitting birds when they defecate. Ants consume the waste, become infected, and the whole cycle starts anew.
The transformation from black ant to red berry form represents the world's first known example of fruit mimicry caused by a parasite. In this case, the victimizer is a parasitic nematode, or roundworm.
The morphing process remains somewhat of a mystery, but the research team has a few theories as to how it happens.
"We think the worms either sequester pigment compounds from the exoskeleton or they make the exoskeleton thinner -- or maybe both," Stephen P. Yanoviak told Discovery News.
"The gaster (infected ant abdomen) does not actually take on a red pigment," added Yanoviak, an insect ecologist 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."
Yanoviak and his team observed that infected ants hold their berry-ish bellies in an elevated position, which is an alarm posture in ants. Hauling around such a blob also makes the ants sluggish. Like ripe fruit, the gaster easily breaks off, so the combination of effects makes the "berry" easy for birds to pluck.
Normally, birds avoid consuming ants because they taste awful, they sting, have spines and possess a hard exoskeleton. The effort simply isn't worth the minimal nutrition ants could provide for birds in high canopy tropical forests ranging from Central America to the lowland Amazon, where the ant-to-berry phenomenon plays out on a daily basis.
The parasites even seem to make the ants more palatable to the birds, which think they are eating a berry from a Hyeronima tree, or one of the many other types of red berries found in tropical forests of the region.
"Infected ants seem to produce much less nasty pheromones," explained Yanoviak, who co-authored a paper on the new parasite with colleague George Poinar Jr., the world's authority on nematodes that parasitize insects. Their paper will be published in the February issue of Systematic Parasitology.
The key to the process is the fact that ants collect bird droppings, which are full of insect parts, seeds and also, by default, roundworm eggs. Ants feed the bird feces to their own larvae. The parasites in the poo hatch and travel to the tiny ant's gaster, where they mate and multiply. The victim ant then leaves the nest looking like a ripe berry.
Steve Heydon, curator and collections manager at the Bohart Museum of Entomology at the University of California at Davis, told Discovery News that "quite a few parasites do weird things to their hosts."
He shared how one trematode parasite actually exerts a sort of mind control over certain ants, causing the ants to climb up grass stalks, clamp on and basically wait to be eaten. The consumer then poops and starts the trematode's life cycle again.
An even more unusual process affects snails, according to Heydon.
"Parasites can infect certain snails, causing their eyestalks to change color, swell and snap off," he said.
Like the bug in a Mexican jumping bean, the parasites in the snail eyes then cause the eyes "to wiggle, which attracts fish that eat them, allowing the parasite to move into its next life cycle stage."
How such behaviors evolved mystifies both Heydon and Yanoviak.
"I have no explanation for it," Heydon admitted. "Parasites are simply amazing creatures. Their life cycles are astounding."
http://dsc.discovery.com/news/2008/01/17/parasite-ant-berry.html
