The aggressive Brazilian ant Crematogaster ampla has a free rider problem. Imposter ants copy its body language. They infiltrate its territory, follow its scent trails, and mooch from its food sources. But for now these infiltrators must avoid touching their hosts, because something about them just doesn’t smell right.
The imposter is the mirror turtle ant Cephalotes specularis , as described in a new study by Scott Powell, an ant biologist at George Washington University. The way Ce. specularis “mirrors” Cr. ampla on jaunts through Cr. ampla ‘s heavily guarded territory is a never-before-seen stage in the evolution of social parasitism, or when one organism hacks the culture of another.
“This is literally the discovery of a species and a new parasitic syndrome at the same time,” said ant ecologist Michael Kaspari of the University of Oklahoma, who was unaffiliated with the work. “It’s the best kind of discovery science.”
Even in the world of ant parasitism—a world of slavery and Manchurian-candidate queens — Ce. specularis is weird. Powell first noticed the species out of the corner of his eye, in the midst of a swarm of Cr. ampla on a baited tree .
“Something I’d just seen wasn’t quite right,” he said. “There were these two or three ants that were almost identical to the host ant, but just sort of dodging around in amongst the chaos.” Powell and his Brazilian colleagues were intrigued. What kind of intruder was this?
The Brazilian cerrado , where both ants live, is wooded savannah. As many as 20 ant species can coexist on a single tree. Yet Powell’s team didn’t find any other ant species at nearly 200 of the host Cr. ampla’s feeding sites, likely because of the zeal with which Cr. ampla chases—and then dismembers—foreigners. No other ants, that is, except the turtle ant Ce. specularis .
While most other turtle ants adopt squat, defensive stances, Ce. specularis protects itself through mimicry. Unlike even their own soldiers, foraging Ce. specularis worker ants are dark and shiny, and they walk with their rear ends raised up in the air—all to dupe the host Cr. ampla. They even copy the same walking speed and stilt-like posture.
This lets mirror turtle ants “pass” in hostile territory, granting them access to the same food their hosts find. Although mirror turtle ants live separately from their hosts, their nests are exclusively found in Cr. ampla ’s domain, suggesting deep dependence. Lab work shows that Ce. specularis ants are drawn to the pheromones marking Cr. ampla scavenging trails even more than the signals left by their own species.
That tension, between free living and dependence, is what makes Ce. specularis so interesting. Evolution treats successful species like Cr. ampla as obstacles in a landscape, forcing other creatures to find ways to go around—or through. Parasitism is a fascinating option, Kaspari said.
“Parasites were the first neurobiologists,” he said. “Natural selection has provided ample opportunity for one organism to mess with another organism, to exploit it by understanding how it perceives the world.”
Although the mirror turtle ant has appearances down, it still hasn’t fooled its host’s finely tuned sense of smell. When traffic is congested along Cr. ampla trails, Ce. specularis skirts the edges, shuffling out of the way to avoid contact. If jostled together, Powell’s team observed, the host ants do a “double-take.” But before Cr. ampla can take up arms, the intruders have already fled.
The endgame, for many parasites, is seamless integration and dependence. But Ce. specularis isn’t there – at least not yet. Regardless of whether the mirror turtle ant is heading down that road, its current semi-independent lifestyle makes it easier to study than parasites who cohabitate with their hosts.
“You’re offered a lot of opportunities to understand some of the costs and benefits of that evolutionary transition from free-living to parasite,” Powell said. With “a deeply entrenched parasite, you can never tease those things apart.”
Finding such a unique relationship takes careful attention and knack for details, Kaspari notes. Dedication doesn’t hurt, either. Building off earlier studies, he said, Powell attracted his ants with a high-sodium bait the paper refers to as “vertebrate urine.”
“His team fills up bottles every morning,” Kaspari said. “They really give 110%.”
Photo credit: Scott Powell