Transmitting behavior between groups

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.

Screen shot 2013-07-17 at 10.30.46 AMAnt 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?

References

Gordon DM (2013). The rewards of restraint in the collective regulation of foraging by harvester ant colonies. Nature, 498 (7452), 91-3 PMID: 23676676

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2 thoughts on “Transmitting behavior between groups

  1. Cool! Can you explain the figure a bit? It doesn’t make sense to me.

    An alternative (although technically falling under cultural transmission) is that when viewed as a dynamic system, the foraging behavior has two (or more) basins of attraction that result in different foraging regimes that perpetuate themselves. Thus the behavior would depend not on some long-term cultural memory but just on the initial conditions of how frequently the first few ants wandered out and locked the system into some regime; after that it is just a self-perpetuating mechanism. Since the first few ants to wander out would with higher probability resemble the pattern of wandering out of their parent colony, they would be more likely to lock into that regime.

    This could be shown in an agent-based (or even analytic) model relatively straightforward, but I am not sure how you would do this experimentally. The only idea that springs to mind is to randomly replace some fraction of ants in the colony by those from a different colony that were carrying out a similar behavior (say resting) when captured. However, you would need a way to account for the ants freaking out about recently being captured and moved ant-hills… not to mention that ants probably know if a given ant is from the same ant-hill or not.

  2. This is fascinating research, I was not aware that there are such differences between ant colonies or that that can transmit different behaviours in that way. Interesting stuff!

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