Ants are among a select number of animals that have attained eusociality, a rare social organization characterized by division of labor, cooperative care for brood, and an overlap of generations. This social organization has allowed ants to function as a superorganism, where each member fulfills their role for the betterment of the group and ultimately helps maximize productivity and resources.
In this article, we’ll define eusociality and discuss how and why exactly ants are eusocial.
What Is Eusociality?
Eusociality is a form of social organization found in select insects such as bees, wasps, and most particularly, ants. It features cooperative behavior among individuals of the same species and is according to E.O. Wilson, characterized by the following:
- Division Of Labor
- Cooperative Care For Brood
- Overlap Of Generations
In this social structure, each organism performs specific roles for the betterment of the group. This lets them maximize productivity and resources such as food and territory, which then allows for relatively easier and safer development as compared to solitary individuals.
How Are Ants Eusocial?
Ants qualify as eusocial organisms simply due to the fact that they possess the aforementioned characteristics. In fact, eusociality is rather explicit in ants, as every member of the colony performs their respective roles and they work together to form what we can consider to be a superorganism.
But to be more specific, let’s look at several examples of ants demonstrating eusociality.
Division Of Labor. The most obvious manifestation of division of labor in ants is in reproduction, wherein only queens are able to reproduce while all other females essentially become their helpers. Apart from that, ants may also further segment roles depending on factors such as age and colony demand. For example, in some species, younger workers are assigned internal tasks while older ones go out to forage.
Cooperative Care For Brood. With reproductive division of labor, queen ants don’t bear the burden of taking care of the colony brood alone. Instead, workers make sure to share the responsibility as they tend to eggs and larvae by feeding and keeping them clean.
Overlap Of Generations. It isn’t uncommon for ant colonies to include multiple generations of ants. In fact, it’s simply part of their life cycle. Queens produce generations upon generations of workers to allow the colony to grow.
Why Are Ants Eusocial?
As a rare social organization, there is no definite reason as to why ants are eusocial. That said, studies on ants and social evolution have led to several theories. One of which is the kin selection or inclusive fitness theory, which for four decades was seemingly well supported and widely accepted.
Kin Selection / Inclusive Fitness Theory
The theory states that when evaluating an action, inclusive fitness is defined as the sum of the effect of this action on the actor’s own fitness and on that of the recipient multiplied by the relatedness between actor and recipient, where recipient refers to anyone whose fitness is modified by the action.
In other words, the theory suggests that an altruistic act that supports the survival of related individuals theoretically enhances the genetic fitness of both actor and recipient, which therefore enables them to pass genes to subsequent generations.
This was derived from W.D Hamilton’s inequality R > c/b, which states that a behavior is favored by natural selection if relatedness (R), as expressed by the fraction of genes shared between the altruist and the recipient due to common descent, is greater than the cost to benefit ratio (c/b). It was also further supported by the haplodiploid hypothesis which suggests that it’s beneficial for ants to raise their sisters (R= ¾) instead of having their own offspring (R=½) due to a higher degree of relatedness.
As time went by however, contradicting information on the subject matter led to the theory failing. For instance, termites and some other eusocial species such as ambrosia beetles were discovered to not use haplodiploid sex determination. And thus, essentially meant that the haplodiploid hypothesis had nothing to do with eusociality.
Standard Natural Selection
An alternative theory suggests that eusociality evolved through a series of stages of standard natural selection. These stages are as follows:
- Formation of groups within a freely mixing population due to the perceived benefits of cooperation.
- Accumulation of traits which make a group tightly formed, which therefore makes eusociality more likely.
- Emergence of eusocial alleles by either mutation or recombination which promote the persistence of the group. For example, millions of years ago, the earliest ant workers started to become wingless making them more likely to remain in their nests.
- Emergent traits created by interactions in the group become subject to environmental forces and natural selection. For instance, one hypothesized key element in the origin of eusociality is defense against enemies and how that affects the overall makeup of the group.
- Multilevel selection drives the evolution of very specialized and elaborate social systems.
While the standard natural selection theory provides a framework for how eusociality evolved, further research is necessary to pinpoint exactly how ants among other eusocial species achieved such a high form of social structure.
It goes without saying however, that like the kin selection or inclusive fitness theory, current theories on eusociality may become subject to future contradictions which may lead them to be discarded. Nonetheless, any new discoveries or ideas should only get us closer to understanding this rare phenomenon.
While rare, ants have somehow attained eusociality, a social organization characterized by division of labor and the division of adult members into reproductive and non-reproductive castes. This has allowed ants to maximize productivity and resources, and has helped them become the most numerous insects and animals in the world.
How they got there though, is still a mystery.