As examples of highly social, structured, and often single-minded species, ants easily pique the interest of biologists and even scientists as a whole. Similar to bees, their colony structure exists as highly divergent from the rest of the multicellular life in the world. Most of it, at least.
They can be viewed, in a way, as closer to the clonal groupings of bacteria than to other insects or any other “higher” level species on the tree of life. Other organisms may share mating spots or even work together to form communities, a la humanity, but it is clearly not on the same level as what ants are capable of achieving.
A term often applied to colony-based species like ants is “superorganism”, where all the individuals act with a sort of hive mind and single purpose of benefiting the colony as a whole. While such a mental link is, as of modern scientific understanding, non-existent, these species still act with a sort of lock-step that implies that something directs their actions.
The Difficulties Of Breeding
Researchers at The Rockefeller University in New York City wanted to investigate this social and mental link within such species. Previous experiments in the past have shown that scent receptors and odors are how the ants communicate with each other so perfectly. The researchers knew, or at least highly suspected, that it was directly genetic in origin, somehow, and they wanted to find the genes responsible. But therein lied the rub. To directly test genetic changes or gene knockouts to determine functionality on ants is a difficult task.
Unlike mice or really any other organism, species that rely on strictly social hierarchies such as ants are incredibly problematic to modify. The complicated life cycles and requirement of being raised directly by other ants means that any modified eggs might be rejected by the colony’s workers. And it doesn’t help that ant eggs are very delicate in the first place, meaning any alteration to them is noticeable by other ants.
The scientists were able to get around this problem though by carefully selecting the species of ants to work with. They chose clonal raider ants (Ooceraea biroi). As you might suspect from the first part of their name, this species of ant are special. They do not use queens to produce offspring, they don’t have any queens at all in fact. Instead, they reproduce clonally, with each individual ant laying an unfertilized egg containing a clone of herself.
An Amount Of Effort
This unique process made it much simpler for the researchers to modify the clonal eggs and even study the effects generationally. And, again as one would expect, they used CRISPR for this purpose.
That’s not to say that there weren’t complications even with these special ants, however.
For their genetics test to work properly, they desired a large enough population of genetically modified ants within the test colony, requiring a lot of eggs to be modified. Unfortunately, the eggs of ants, for this species at least, release a chemical signal that stops other ants from laying eggs while that egg is still hatching.
Getting around this required a large amount of synchronization and probably several excel spreadsheets in order to produce enough modified ants. Even so, it took two years, with a fair amount of that being due to the eggs breaking every time they tried and the eggs being rejected by the ants until the researchers learned how to return them in a way that wouldn’t give away the modification.
The Worth Of A Gene
Once all that was accomplished, they could get to the real work. The focus of their test was on a particular gene known as orco, which had been known to produce a protein that helped the function of the ants’ odor receptor cells in their antennae.
What they found is that without the orco gene functioning, the ants did not develop their odorant receptors properly and began immediately wandering around the nest even as babies. This wasn’t normal and they also did not seem capable of noticing or following the trails left by other ants. Nor did they understand the idea of working together in groups with other ants to accomplish tasks.
Additionally, the transgenic ants laid fewer eggs and at longer intervals. The last nail in the coffin was that they died much sooner than other ants as well, living only half as long.
Closer investigation into the interior structure of the modified ants found that lacking the orco gene had significantly altered the brain areas related to the odorant receptors, with the clusters of cells known as glomeruli never forming.
Evolution And Cross-Species Connections
This defining characteristic the orco gene confers appears to relate directly to social behavior and the formation of colony structure through scent receptors. Interestingly, other insects, such as the model organism Drosophila melanogaster (common fruit fly), did not lose their glomeruli when the orco gene is deactivated in their genome, implying that there are additional genetic changes tied into the gene in ants in particular that cause that effect.
Determining the genetic mechanisms that lead to the development of social hierarchies in species like ants allows developmental comparisons of brain structure to other organisms as well and how closely related complex activities are to the evolution of sociality.
This, in turn, not only helps explain brain development more, but also the directions that evolution has taken over the history of life on Earth.