There’s never enough ant coverage in Nature Documentaries. Ants are a paradigm for self organizing systems. Here you can watch two TED lectures by the prominent ant scientist (Myrmecologist) Deborah Gordon of Stanford University. She has been studying red harvester ants intensely both in the field and in laboratory. Observation of ants in both environments have been very informative in understanding emergent properties of a complex system such as an ant colony.
How does a living system with no central control function? How do they partition tasks? Do worker ants do the same job all their lives or do they switch tasks? What is the collective decision making process during times of stress? How does information flow inside and outside the nest? Do worker ants search food with an innate hardwired behavioral pattern? Do they show individual variations in their behavior? How does a colony manage it’s resources? These are just a few curious questions among the many others for generating hypothesis. These hypothesis are being tested by scientists who make detailed observations and design experiments. Results help us build a theory on self-organizing systems.
Ants are wonderful systems to understand human nature as well. Ants, bees and wasps make up only 3 percent of animal diversity yet they may constitute up to 25 percent of the total animal biomass in land habitats. They can play such immense roles in nutrient cycling that they are also called “ecosystem engineers”. A mature leaf-cutter ant colony can consume leaves equal to the weight of a cow every day! During the ambitious Biosphere II experiment ants displayed some of the most significant biological activities within the enclosure.
Ant evolution began more than 130 million years ago. Scientists have been observing and measuring their behavior both in their natural environments and also in laboratory. It is possible to raise ant colonies in captivity and test hypothesis by designing experimental nest set ups. There’s a growing ant keeping hobby movement from all over the world. Inside well-designed formicariums it is possible to maintain colonies of massive sizes. Ants have been sent to International Space Station as a part of the collective expandable search experiment championed by Deborah Gordon.
Ants exchange information through smell. Antennae are highly sensitive smell organs. Gordon explains how simple interactions among workers produce an emergent property (a concept used by complex systems researchers) such as recruitment to defense or nest maintenance or foraging activities that adapts the colony to survive through changing situations.
The image below is taken from a study in Gordon Lab showing how red harvester ant workers search in an arena that connects nest chambers with the out world designed to simulate foraging area for ants in captivity. The colorful network represents 131 individual ant paths overlaid on top of each other. Immediately below the image you can see the arena with two plastic pipes appearing as entrances from two sides. The strikingly visible pattern is that ants follow straighter paths when the worker density is reduced (see walking pattern inside the pipes). Inside the arena worker density is higher and thus increased interactions lead to more scattered paths. This is one example for expandable search network. How different ant species adjust their search network is a curious question. Invasions by many introduced ant species can be explained by their search network. Invasive ants may have more efficient search behaviors in finding resources. Expandable search network is now a citizen science project to be tested on different species of ants by school kids all over the world.
Understanding interactions among agents in a system can inform us in many ways. Disease transmission during outbreaks is influenced by such interactions among humans. An RFID-tag study carried out in a hospital pretty much employing the same idea from ants. The study has shown that nurses are the most vulnerable and transmissive group.
Unlike many ant species who rely on pheromone trails to recruit workers to food sources, harvester ants don’t do this. In desert environment pheromone trails are not efficient. The body size of harvester ant workers evolved to maximize self-sufficiency. These ants collect seeds that are scattered over large areas and workers are large enough to carry seeds by themselves. These ants however continue use smell cue very heavily to communicate when they touch each other by their antennae. Antennae mediated communication is the major way colonies adjust their foraging activity without knowing what is going on outside the nest. There’s a dynamic relationship between foragers returning with food and outgoing foragers preparing to leave the nest on the next foraging trip. Ants use the rate of brief antennal “high-fives” inside the nest to adjust numbers of workers leaving the nest. In desert water source of the colony are stored in seed tissues. In very hot days most colonies restraint their workers to stay inside the nest.
Gordon’s studies have shown that colonies show variation in foraging behavior and genetically related colonies resemble each other in their foraging decisions. There must be a heritable genetic component in behavior. Heritability of nest building ability has been shown in deer mice who show a striking variation in nest burrow architecture. Nest building behavior is controlled by a surprisingly few (only 4!) number of genes. See the video below analyzing nest construction behavior in mice under laboratory conditions:
Old colonies are more consistent and homeostatic and young colonies were more variable and experimental. What is the genetic source of this variation in ant behavior? Genetic analysis will eventually answer this question. Database of ant genomes continues to grow.
Gordon and her co-workers’ studies have shown that allocation of task within the nest changes. There’s also an interesting fact that not all ants work. Unlike our stereotyping most ants do nothing. They may be “reserve ants” recruited and mobilized only when a crisis situation (nest cave ins, floods, enemy invasions, rapid larvae evacuations etc.) takes place.