Farmer Ants
Texto y fotos: Javier A. Pinzón
Can ants grow their own food? Yes, and not only that, but they also use agricultural techniques to nourish, fertilize, detoxify, protect, spread, and grow the fungus on which they feed. And, to top it all off, colonies use a complex waste management system to prevent possible invasion by harmful fungi.
Hermógenes Fernández-Marín, a scientist at the Institute for Scientific Research and High Technology Services (INDICASAT-AIP), whose, the headquarters of which is located in Panama, began studying ants in 1999 and continued these studies as the basis for his masters, doctorate, and two post-graduate degrees, the latter from the University of Copenhagen in Denmark and the Smithsonian Tropical Research Institute in Panama. Fernández-Marín’s studies focus on ant biodiversity and behavior and particularly the characteristics that allow ants to adapt to changing environments and control disease in their colonies. Most of his time, however, has been occupied by behavioral studies of fungus-growing farmer ants and their parasites.
We meet early in the morning at his laboratory and set out for Gamboa, a village in the heart of the Panama Canal watershed, encircled by the waters of the Chagres river and Gatún lake and shaded by a dense, unspoiled forest. As soon as we arrive, the scientist drops his belongings in his office, tightens his boots, and leads me to his control colonies. The first thing he points out as we walk along is that the leaves carried by ants are not food; they are used instead to grow a fungus that is part of the Basidiomycetes group of fungi.
Hermógenes decrypts information about his colonies with the same ease as an architect reading the intricacies of a city from a map. For example, the number of entrances to a colony will tell you its age: if the nest has only one entrance, it’s probably only a year old, by two years it will have three to five entrances, and by the third year it will have more than ten.
Fernández-Marín uses a geologist’s pick to dig gently until he hears a hollow sound, then changes to a tool with a blade. He is searching for the chambers, to remove a portion of the nest and the fungus inside it. He works patiently and resembles an archaeologist in front of Panamá’s El Caño tombs. He explains that, with the arrival of the first rains, millions of queens will fly out of the mother colony on something called the nuptial flight. It is their only opportunity to copulate. Depending on the species, they will couple with anywhere from four to eleven males. Each queen tries to accumulate as many sperm as possible to fertilize the eggs in the colony she will found and maintain throughout her lifetime. Each ant colony begins with a single ant: the queen. As soon as they land, they dig a chamber, start growing the fungus, and lay their first larvae, from which the colony’s first worker ants will emerge. There are two types of queen fungus-farmer ants: those that leave the colony to forage, and those with enough resources to metabolize for three to four months, until their first workers begin to forage.
Each colony is home to three types of ants: males, produced only during the breeding season; queens, who seek males to create their future nest; and wingless worker ants. In some species, all workers are the same size, and in others the size and shape varies, creating sub-castes. The genetics are the same; the difference lies in the amount of food ingested during the growth stage, which depends on the colony’s needs.
As they evolved from forager ants, these ants developed an agricultural system that allowed them to establish a foraging area, which in turn led to a more sedentary life. This made it possible to increase the number of individuals in a society, but also created a problem, since the threat of disease increased, and food supply became a challenge.
The supply problem was solved by an exclusive focus on cultivating a single type of food. First, the workers leave the nest to forage, which will be their job for the rest of their lives. They choose leaves that hold water well and carry them to the nest. How do they select these leaves? How do they forage? This remains unclear, but certain studies confirm that ants modify their foraging trails to limit transportation costs and ensure that materials reach the nest in the most efficient manner possible. When a worker arrives at the nest, it delivers the leaf to another ant in charge of using antibiotic secretions to clean the leaf and remove any fungus or bacteria.
In fact, depending on the genus, farmer ants maintain their waste management systems using a number of different strategies. For example, the majority of fungus-farming ants in the Trachymyrmex genus, who live in small colonies of 50-200 individuals, are equipped with Actinomycetes bacteria, from which they extract the antibacterial compounds needed to combat the pathogenic fungi that attack the fungus they grow. Ants in the Sericomyrmex genus, whose colonies are larger and contain 2,000-3,000 individuals, lost their bacteria and started using the antibiotics produced inside their glands. The same is true of leaf cutter ants in the Acromyrmex genus, that live in colonies of 150,000-200,000 individuals. They use Actinomycetes bacteria as a primary source of antibiotics, while ants in the Atta genus, whose colonies number up to 8 million individuals per nest, lost their bacteria, but use antibiotics produced in their glands. Undoubtedly, the use of antibiotics has facilitated the development of more complex societies.
After the leaf is cleaned, it is cut, macerated, and sprinkled with ant “feces,” which contain growth enzymes to stimulate development of the fungus. Finally, they cut small bits of the fungus and place them on top of a new leaf to grow. The fungus “garden” is then shaped in a process that can take up to five hours. A very interesting relationship is apparent in this agricultural strategy: the fungus changes to allow for growth and the ants change to be able to grow it. The ants lost their stingers and developed stronger jaws, which allowed them to cut the leaves and sets them apart from the primitive hunting systems used by most ants. Meanwhile, fungi have adapted by developing grape-like structures called Staphylococcus.
Ants cut and chew the Staphylococcus and feed them to their young. Adults eat some of the fungus and the fluid from the leaves they cut. However, scientists still don’t have a clear understanding of how adults who do not leave the colony are nourished. The symbiont fungus is also used to protect the young, which are wrapped in this fungus to prevent the spores from other fungi and bacteria from germinating. But, if despite these efforts spores manage to germinate, the ants can slow their growth and gain time enough to remove them.
Ants are nevertheless constantly forced to deal with disease management since a single sick individual can infect the entire colony. Leaf cutters in particular have synthesized phenylacetic acid (PAA), a powerful chemical secreted by the exocrine glands in their bodies that protects against bacteria and fungi. Interestingly, ants only use this antibiotic when they are ill or suffering from a fungus or bacteria-related infection.
One of the ants’ main enemies is a fungus in the Escovopsis genus that co-evolved along with the fungus they farm. A relationship exists between PAA and the Escovosis genus since ants have used this antibiotic for eight million years to combat the fungus. How is it possible for a single antibiotic to remain successful for so long, and why has no resistance to it yet been detected? The answer lies in a waste management system, which includes constant monitoring to eliminate pathogens. Ants have established a strict division of labor: individuals that handle waste never come into contact with those working in the garden or those who forage. These individuals are practically an untouchable caste: they handle waste until they die, and once they begin this work they never return to the garden.
Hermógenes has finished digging and removed the fungus, the queen, and a section of the colony. This treasure will be taken to his laboratory to be added to the hundreds of colonies used to research ant’s behavior with regard to pathogens, the use of antibiotics or bacteria, and the epidemiological and public health patterns of different ants faced with pathogens. In search of findings related to the latter, he removes a bit of fungus, places it on several Petri dishes, and waits for a pathogen to grow in order to isolate it in a pure culture and learn more about how aggressive it may be and the dynamics of infection in the nest.
By studying these mechanisms we can better understand the success of ants and perhaps apply this principle to humans. It seems that certain ants have used a small group of antibiotics, like PAA, since their beginnings without developing resistance to it, while humans become immune to new antibiotics over a very short period, in some cases from 3-5 years.
We’ve been using antibiotics for ninety years (since the discovery of penicillin), whereas certain ants have been using them for at least 120 million years, and farmer ants for at least 60 million years, with apparent success.
There remains much to discover and learn about these small insects, so it is important to fund institutions like INDICASAT-AIP, which supports human resources in basic and applied sciences in Panama, and works to raise awareness in the government and other institutions regarding the importance of generating knowledge and investing in research and development.
