The evolution of interacting phenotypes: genetics and evolution of social dominance

Although the argument over genetic influences on social dominance is contentious, genetic models of interacting phenotypes provide a theoretical framework for heritable effects on, and therefore evolution of, social behavior. Here we adapt the interacting phenotype model to show how social dominance can evolve. Our model makes a number of predictions: rapid evolution of behavior, strong correlated responses in associated traits (such as a badge of status), and, because context is important for social dominance, integrated evolution of both dominant and subordinate behavior reflecting direct and indirect genetic effects and social selection. We also describe the results of empirical work, artificial selection based on social status within a hierarchy in the cockroach Nauphoeta cinerea, that we used to test the predictions of our model. There was little change within selection lines in the expression of agonistic behavior, but by just generation 7 of selection, in comparisons between lines, high-line males consistently dominated low and control males, while low-line males were consistently subordinate to high-line and control males. There was a strong correlated response to selection in the pheromonal badge of status. Some correlated responses to selection differed among replicate lines, with the compound that makes males subordinate changed in one replicate, while the compound that confers dominance was altered in the other. Overall, our results are consistent with predictions from models of interacting phenotypes: social dominance is influenced by additive genetic variation, can evolve as a result of social selection, and evolution of social interactions appears to be rapid. Finally, different responses in the replicates allowed us to test very specific predictions regarding the role of the social pheromone in N. cinerea, highlighting the value of artificial selection experiments as a tool in evolutionary behavioral genetic studies.