Cognition and evolution in social insects

Some articles recently came into my news feed that illustrate nicely the dilemma of cognition, genes and social evolution.

Two articles come from two groups of researchers which were examining the genetics of brain development in ants. They used an advanced gene-editing technique called CRISPR to create a lineage of ants that carried a mutated and non-functional version of the gene orco, which encodes for a receptor for the odorant molecules, called pheromones, that ants and other social insects employ to communicate with one another. In insect societies, these pheromones play an important role in organizing the social life of the colony.

In the ants with the mutated receptors, the social organization of the ant colonies was disastrously disrupted. No surprise there: the mutation effectively blinded the ants to all the signals from their nestmates that allowed them to organize themselves into a superorganism. They also found that the mutated ants suffered degradation of those regions of the ant brain that process those pheromone signals. Again, no real surprise there: it is common for the parts of the brain that process sensory signals to need input from sensors to develop properly. In animals blinded from birth, for example, those parts of the brain that process visual sensory information differ substantially from the brains of animals that have normal eyes.

What was surprising to me is what the researchers conclude. To quote from their abstract: “The development of genetics in [these ants] establishes this ant species as a model organism to study the complexity of eusociality.” Let me translate a bit. “Eusociality” refers to the complex social systems found in the ants, bees and termites. The evolution of eusociality and the superorganism is a big problem in evolutionary biology. These researchers are taking the position that we can understand the evolution of these complex societies as a matter of genetics.

Really? I don’t begrudge them the hope, but what can genetically blinded ants tell us about the evolution of sociality? Color me doubtful, I guess.

Fueling my doubt is an accompanying article (not a paper yet, this is from a news article (link below) about a group of European researchers.) about how the pattern of ant pheromones varies in related lineages of ants. Some background: the chemical communication among ants involves semi-waxy molecules that are secreted onto the ant’s exoskeleton, called cuticular hydrocarbons (CHCs). These CHCs are smelled / tasted by other ants, and serve the ongoing communication amongst nestmates. The chemical communication among ants is extraordinarily rich: ants sense not only individual molecules, but mixtures of molecules. Think of it as a kind of painting. You can make up millions of colors by various combinations of just four primary colors (Cyan, Magenta, Yellow, Black: the CMYK color profile). In the same way, ants can use just a few types of CHC to paint themselves with an extraordinary range of pheromone “colors.”

These researchers were curious how closely related ant species could distinguish themselves from one another, using their different patterns of CHCs. They expected that the diversity of CHC patterns would closely reflect their genetic lineage. In other words, they expected that a species “pheromone color” would mark lineages quite closely, as if species A was red, species B blue, species C yellow and so forth.

What they found instead was a much richer pheromone coloration that reflected adaptive conditions. As if, for example, species A would paint itself red in some situations, orange in other circumstances, mauve in still others. In other words, pheromone coloration communicated both species identity, and adaptation.

Returning then to our mutant ants, what could a mutation that effectively blinded ants to this extraordinarily rich sensory landscape tell us about the evolution of a complex phenomenon like sociality? Again, color me skeptical.

I wrote about this problem in Purpose and Desire, and phrased it this way. The notion of sociality as an expression of “sociality genes” cannot really tell us much about the evolution of these remarkable social systems. What makes more sense is to treat the evolution of complex societies as an expression of cognition, which is what really drives lineages forward in time: evolution.

References

Trible, W., L. Olivos-Cisneros, et al. Orco Mutagenesis Causes Loss of Antennal Lobe Glomeruli and Impaired Social Behavior in Ants. Cell 170(4): 727-735.e710.

Yan, H., C. Opachaloemphan, et al. An Engineered orco Mutation Produces Aberrant Social Behavior and Defective Neural Development in Ants. Cell 170(4): 736-747.e739.

https://phys.org/news/2017-08-chemical-profile-ants-rapidly.html

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