By Adrian Smith; taken from Myrmecos.
Crowds chanting in unison, wolves hunting in a pack, the superorganism that is the ant colony: these are all things that require the coordination of many individuals to accomplish something that they could not on their own. And yet, replace any individual with another and the behavior will turn out pretty much the same. Right?
Let’s look at the example of colonies of harvester ants that forage in the desert for seeds. These ants adjust their collective foraging behavior through small interactions between individuals: ants decide whether to leave the colony to search for food if they sense other successfully returning foragers. This way, if a lot of ants are returning with food, more ants will leave because the world is feeling bountiful. But if few ants are returning with food, fewer new ants will leave to search; it’s just not worth it when there’s not a lot of food out there. After all, leaving the colony carries a cost. Every moment in the desert desiccates the poor ant foragers, and if they stay out too long they’ll up and die.
Ant colonies don’t forage every day. Their foraging depends not just on the abundance of food, but on environmental conditions such as heat and humidity. Beyond this, there are colony-specific traits. Some colonies will forage every day, some will just forage some days, and this trait persists across years. This is trait is somewhat transmissible as colonies that reduce their forage on an uncommon day also have daughter colonies that are likely to reduce their foraging on uncommon days. This transmission of collective behavior suggests that responses to environmental conditions can be transmitted from one colony to the next. This is the human equivalent of a teenager from Scandinavia founding a new town in the midwest and recapitulating parts of his culture there…
It’s not clear what the mechanism here is. Since daughters of a queen continue to forage in a colony-specific manner, the transmitted component must be unrelated to the genetic contribution of the father. So is it genetic, and linked to the X chromosome? Or is it in some sense cultural, learning from the behavior of the greater colony it was raised in? Hopefully someone who knows more about young ant behavior can enlighten us here…
Either way is interesting. I can certainly imagine that a dynamic, collective behavior is controlled genetically. Dopamine receptor expression is linked to foraging behavior, so genetic differences here could easily transmit motivation to forage. And yet – cultural transmission would be pretty exciting, too. This would indicate there is some sort of learned component and makes me wonder: if we can measure all the movement of an animal throughout its life, how well could we predict the behavior of a whole group?
Gordon DM (2013). The rewards of restraint in the collective regulation of foraging by harvester ant colonies. Nature, 498 (7452), 91-3 PMID: 23676676