Fossil Find: Fungus Controlled Ant Just Like Today

The fossil record cannot usually tell us about the soft body parts or the behavior of its specimens. For these, we look to the extant species. But now a clever finding reveals an odd behavior in carpenter ants from the distant past.

Nature is full of designs and behaviors not easily preserved in the fossils. Consider the bat, certain types of which map out objects around it as small as a mosquito by sensing the echoes of its own squeaks—a system known as echolocation. The bat emits a high-pitch squeak, well beyond the range of human hearing, up to 2,000 times per second. Next it determines both range and direction to the tiny mosquito by sensing the echo while filtering out echoes from the squeaks of nearby bats. Or consider fish that use underwater electric fields either passively or actively to sense objects around them, including other fish.

It is difficult to determine such details from the fossil record, but they reveal how unlikely is the theory of evolution. Anyone familiar with today’s sonar or radar systems knows the immense complexity involved with such systems: the problems of sensing the echo in the presence of the transmitted signal which can be billions of times stronger, of filtering out spurious signals such as echoes of older transmissions, of combining the echo information with knowledge of your own motion, and so forth. Yet the bat’s detection abilities are superior to those of the best electronic sonar equipment.

It is also difficult to determine complex behaviors from the fossil record. Consider certain Hydra species, a small underwater creature, that develop nematocysts—stinging cells which eject a tiny poisoned hair. A planarian worm known as the Microstomum, consumes Hydra but passes the nematocysts through its digestive system and positions them on its surface. The Hydra meal serves to arm the Microstomum, and when fully equipped the Microstomum omits the Hydra from its diet, resuming again after discharging its ill-gotten arsenal.

For evolution to have formed this system, certain Microstomum must have happened to have selectively digested the Hydra, leaving the nematocysts untouched. Then they also happened to have vectored the nematocysts to the surface and positioned it there. Then certain Microstomum happened to have a feedback loop installed to regulate its diet.

Or consider a sheep parasite known as the brainworm:

The brain worm that reproduces in sheep uses ants to get back into a sheep. The worms get into ants by infecting snails that eat sheep feces. The snails expel tiny worm larvae in a mucus that ants enjoy, and some dozens of worms take up residence in an ant. But this would do them no good if the ant behaved normally; too few ants would be eaten by sheep. Consequently, while most of the worms make themselves at home in an ant’s abdomen, one finds its way to the ants brain and causes the ant to climb up a grass stem and wait to be eaten by a sheep. Ironically, the worm that programs the ant is cheated of happiness in the sheep’s intestine; it becomes encysted and dies.

The whole procedure seems unnecessary. Why do the worm eggs defecated by the sheep not simply hatch and climb up the grass stem to await being eaten by a sheep instead of making the hazardous trip through snail and ant? How could they become adapted to being carried by the ant unless the ant were already programmed to make itself available to be eaten by a sheep?

The list, of course, goes on and on. There is the decoy-fish with its detachable dorsal fin that mimics a smaller fish complete with a dark spot resembling an eye and notch resembling a mouth. The decoy-fish becomes motionless except for the decoy which moves from side to side, causing the “mouth” to open and close. And there is the owl with ears tuned to different frequencies, to better track its prey, and the rattlesnake with heat-sensitive (infrared) sensors to image its prey at night.

Now, a new fossil finding shows just how persistent nature's odd behaviors can be. A carpenter ant (Camponotus leonardi) can be infected by the fungus Ophiocordyceps. Sensitive to the forest temperature and humidity, the fungus must be up off the ground but lower than the forest canopy. It arrives at the desired height by taking over the ant it infects:

The fungus cannot grow high up in the canopy or on the forest floor, but infected ants often die on leaves midway between the two, where the humidity and temperature suit the fungus. Once an ant has died, the fungus sprouts from its head and produces a pod of spores, which are fired at night on to the forest floor, where they can infect other ants.

Scientists led by Hughes noticed that ants infected with the fungus, Ophiocordyceps unilateralis, bit into leaves with so much force they left a lasting mark. The holes created by their mandibles either side of the leaf vein are bordered by scar tissue, producing an unmistakable dumb-bell shape.

It is another fascinating parasitic action that, it would seem, could never be found in the fossil record. But a team of intrepid researchers found a way:

Writing in the journal, Biology Letters, the team describes how they trawled a database of images that document leaf damage by insects, fungi and other organisms. They found one image of a 48m-year-old leaf from the Messel pit that showed the distinctive "death grip" markings of an infected ant. At the time, the Messel area was thick with subtropical forests.

"We now present it as the first example of behavioural manipulation and probably the only one which can be found. In most cases, this kind of control is spectacular but ephemeral and doesn't leave any permanent trace," Hughes said.

And how did evolution design such a Rube Goldberg device? Who knows:

"The question now is, what are the triggers that push a parasite not just to kill its host, but to take over its brain and muscles and then kill it."

He added: "Of all the parasitic organisms, only a few have evolved this trick of manipulating their host's behaviour.

Evolution is truly amazing. It creates in ways we cannot even figure out.

Religion drives science and it matters.