Tag Archives: sucrose

Acacia tree

Acacia trees deal addiction to bodyguard ants

A strange evolutionary alliance between trees and the ants that guard them has a sinister explanation, a new study suggests, after studying ants hooked on nectar.

Bodyguard ants and addiction

In Central America, ants act as bodyguards for acacia trees, defending them not only from weeds, but also from animals, in exchange for accomodation and food – this has traditionally been seen as one of the most consistent and remarkable alliances in nature.

But Martin Heil of Cinvestav Unidad Irapuato in Mexico reports there’s more than meets the eye when it comes to tree snacks. The tree’s sugary offerings are laced with an enzyme that prevents the ants from eating other sources of sugar – one sip, and they’re hooked to the tree and only the tree, in classic type of addiction.

“It was surprising to me that the immobile, ‘passive’ plant can manipulate the seemingly much more active partner, the ant,” says Heil.

The report illustrates how even in the seemingly mutually advantageous partnerships in nature, one part takes more out of the deal than the other.

Heil compares the situation to a dairy company that sells lactose-free milk chemically altered to render its customers unable to digest normal milk. Drink it, and you can only eat that brand forever.

Sneaky trees

Acacia tree

photo credit: angela7dreams

Ants love eating sweet foods; most of the foods they eat, such as plant sap, are rich in a sugar called sucrose. The ants digest this with an enzyme called invertase, which basically breaks the sucrose into smaller sugars. In 2005, Heil had previously shown that all of the workers of the acacia ant Pseudomyrmex ferrugineus lack invertase – and therefore cannot digest sucrose. Fortunately for them, the tree compensates for this impairment by secreting invertase into its nectar, providing the ants with a predigested meal. Quite a neat trick, apparently, but isn’t it a little just too perfect? It does seem a little strange, how things worked out just fine, so Heil set out to understand what happens behind the curtain.

What he found out was that the tree’s sugary treats not only contained invertase, but they also contained something extra – chitinase enzymes that completely block invertase development in ants. So basically the tree takes away their ability to digest, and instead, offers them pre-digested food, quite a neat, sneaky trick.

“Ain’t nature grand?” says Todd Palmer of the University of Florida, who studies ants and acacias. “What looks from the outside as another case of digestive specialization appears to be a sneaky manipulation on the part of the acacia to increase ant dependence.”

Enzymes and bodyguards

Now, researchers want to go even deeper, and find out exactly how a plant’s chitinase could block an ant’s invertase.

“All the biochemists whom I talked to told me that there is no way one of these enzymes can inhibit the other. There is simply no known biochemical mechanism through which this could happen,” he says. “It adds to our understanding of why co-evolved systems persist even when they may not be required for both partners,” says Corrie Moreau, an evolutionary biologist from the Field Museum in Chicago.

So either he’s missing something, or this is truly a revolutionary mechanism. But there’s another interesting question: why don’t young workers try another food source, while their digestive system hasn’t been tampered? Heil thinks this is because nectar is almost always their first adult meal, either because it is the closest food or because the ants are fed the nectar by their nest-mates.

“Since the first dose of nectar is enough to reduce invertase activity, they remain trapped,” he says.

Scientific Reference: Partner manipulation stabilises a horizontally transmitted mutualism
Martin Heil1,*, Alejandro Barajas-Barron1, Domancar Orona-Tamayo1,2, Natalie Wielsch3, Ales Svatos3

Mutant cockroaches learn to avoid sugar traps

Cockroaches, the blight of every urban apartment; they’re adaptable, they’re sturdy, and they reproduce really fast. The nasty, disease carrying bugs can eat pretty much anything they find around the house, from mold and rotten food to the thing they love the most – sugar.

cockroachWhen given the opportunity, cockroaches always go for the sugary treat – or at least they used to. According to a new study published in Science, some cockroaches have evolved to the point where they are actually refusing to eat sucrose, a form of sugar commonly found in plants.

“They now perceive glucose as bitter,” says Coby Schal, an entomologist at North Carolina State University and one of the report’s authors.

Why did this happen? Well, glucose is the main thing that attracts them in traps, and many of the little creatures have mutated so that they actually don’t like it anymore. They mutated so fast that it took everybody by surprise.

Back when prehistoric cockroaches lived in the wild, there’s a possibility that they didn’t gobble glucose as well, because many plants that contain it in the wild are poisonous – but that’s still debated.

However, as humans evolved and moved to caves, cockroaches were soon to follow. Away from the threat of poisonous plants, they started to develop a taste for sugars, because it is a highly nutritious source of energy, and it was to their advantage to consume it.

But the mutation remained in their gene, and when humans started putting sugar traps, we reactivated the old gene – so much that when we put sugar in front of (some groups of) cockroaches, they just “jump back as though you’ve given them an electric shock“.

Apparently cockroach researchers take their job pretty serios, and they want to dedicate the next decade or so to studying this adaptation.

“We have roaches in the freezer that date back to the 1930’s,” says Schal. “This is what’s going to be driving our research over the next five or ten years.”

But all hope of trapping these mutant critters not lost. Sucrose-averse roaches are still attracted to fructose, or fruit sugar, and maltose, which is found in beer (“they really love that stuff,” says Schal).