Trees Make Ants Chemically Dependent, Turn Them Into Indentured Servants

Trees Make Ants Chemically Dependent, Turn Them Into Indentured Servants

November 12, 2013 | by Lisa Winter
IFL Science

Ants on Acacia Tree

Ants on Acacia Tree (Photo credit: Ryan Somma)

There are all kinds of mutually beneficial relationships that exist in nature in which two seemingly unconnected species live in harmony and provide vital services for one another. This does not always result in both parties benefiting equally – but as long as it still works, it keeps on going. A recent study has shown that certain Central American ants live on and defend a particular tree not because they want to, but because enzymes in the tree’s nectar have made it impossible for them to get food anywhere else. The research team was led by Martin Heil of Cinvestav Unidad Irapuato in Mexico and was published in Ecology Letters.

The acacia tree is covered in pods that can be taken by insects. Colonies of Pseudomyrmex ferrugineus patrol the tree, protecting the pods. Some species of acacia tree even have thorns large enough for the ants to move into. In turn for their defense against predators like termites, the tree produces nectar for the ants. The nectar is rich in sucrose, a type of sugar. Using an enzyme called invertase, the ants break up the large sucrose molecules into smaller bits which can then be used to generate energy. About eight years ago, Heil’s previous research showed that the adult ants don’t even make invertase, but it is produced by the tree and can be found in the nectar. It is a classic textbook example of mutualism, or so we all thought. The truth, as it seems, is a bit more complicated.

Five years ago, Heil found out that young ants do produce invertase, but that ability is lost at some point during life. In recent years, he has searched for the answer which, he would find out, almost seems like one of the biggest betrayals in mutualism history: the tree stops the ants from producing their own digestive enzymes. Included in the sucrose and invertase is chitinase: an enzyme that blocks invertase production.

While it is true that the ants protect the tree in exchange for food, they do so because they have no other options. They are completely unable to eat from any other source, because they rely on the invertase from the acacia’s nectar. So, the tree gives them exactly what they need to live, but only because it made them invertase-deficient in the first place. The tree makes out like a bandit by having armies of ants to protect it, who will never be able to leave.

This methodology has vague (and highly anthropomorphized) connotations to Münchausen syndrome by proxy (MSbP) in which someone believes they are sick and have a dedicated caretaker, but it turns out that the caretaker was the one making them sick in the first place. In the case of the acacia tree, it is damning the ants to an eternity of servitude on top of blocking the invertase production to ensure it is the ants’ only food source.

On a very basic level, however, this is astoundingly impressive. Solely through genetic mutations over countless generations, the acacia tree has adapted a way to protect itself from predators and the ants won’t be able to leave, leaving the tree vulnerable. It just happened to evolve this way, which is absolutely amazing. You win this one, acacia tree.

Chemists show life on Earth was not a fluke

24 October 2013, 6.16am BST

In them, began life. University of Utah

How life came about from inanimate sets of chemicals is still a mystery. While we may never be certain which chemicals existed on prebiotic Earth, we can study the biomolecules we have today to give us clues about what happened three billion years ago.

Now scientists have used a set of these biomolecules to show one way in which life might have started. They found that these molecular machines, which exist in living cells today, don’t do much on their own. But as soon as they add fatty chemicals, which form a primitive version of a cell membrane, it got the chemicals close enough to react in a highly specific manner.

This form of self-organisation is remarkable, and figuring out how it happens may hold the key to understanding life on earth formed and perhaps how it might form on other planets.

The 1987 Nobel Prize in Chemistry was given to chemists for showing how complex molecules can perform very precise functions. One of the behaviours of these molecules is called self-organisation, where different chemicals come together because of the many forces acting on them and become a molecular machine capable of even more complex tasks. Each living cell is full of these molecular machines.

Pasquale Stano at the University of Roma Tre and his colleagues were interested in using this knowledge to probe the origins of life. To make things simple, they chose an assembly that produces proteins. This assembly consists of 83 different molecules including DNA, which was programmed to produce a special green fluorescent protein (GFP) that could be observed under a confocal microscope.

The assembly can only produce proteins when its molecules are close enough together to react with each other. When the assembly is diluted with water, they can no longer react. This is one reason that the insides of living cells are very crowded, concentrated places: to allow the chemistry of life to work.

In order to recreate this molecular crowding, Stano added a chemical called POPC to the dilute solution. Fatty molecules such as POPC do not mix with water, and when placed into water they automatically form liposomes. These have a very similar structure to the membranes of living cells and are widely used to study the evolution of cells.

Stano reports in the journal Angewandte Chemie that many of these liposomes trapped some molecules of the assembly. But remarkably, five in every 1,000 such liposomes had all 83 of the molecules needed to produce a protein. These liposomes produced large amount of GFP and glowed green under a microscope.

Computer calculations reveal that even by chance, five liposomes in 1,000 could not have trapped all 83 molecules of the assembly. Their calculated probability for even one such liposome to form is essentially zero. The fact that any such liposomes formed and that GFP was produced means something quite unique is happening.

Stano and his colleagues do not yet understand why this happened. It may yet be a random process that a better statistical model will explain. It may be that these particular molecules are suited to this kind of self-organisation because they are already highly evolved. An important next step is to see if similar, but less complex, molecules are also capable of this feat.

Regardless of the limitations, Stano’s experiment has shown for the first time that self-assembly of molecular machines into simple cells may be an inevitable physical process. Finding out how exactly this self-assembly happens will mean taking a big step towards understanding how life was formed.