Conflict, Cooperation and the Evolution of Conditional Social Behaviors in Colonial Marine Invertebrates

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Grosberg 9906741The tension between conflict and cooperation drives the evolution of social behavior, occasionally leading to permanent transitions in social organization. More commonly, however, the tension results in the evolution of transitory social liaisons among conspecifics that form, disintegrate and reform from place to place and generation to generation. Underlying many of these transient associations is a spectrum of plastic behaviors -some altruistic, some selfish - whose expression depends on the social environment provided by interacting conspecifics. Current theories of social evolution build on the fundamental role of kin selection, while acknowledging that other facets of the social environment influence the costs and benefits of altruistic and selfish behaviors, hence the conditions under which they should be expressed. All else being equal, individuals should direct altruistic (or cooperative) behaviors toward relatives, and selfish behaviors away from relatives. Individuals should also modulate the expression of altruistic and selfish behaviors according to the prevailing social environment and their own ontogenetic state. Finally, changes in the social environment experienced by different species should promote the diversification of social behavior.Despite the ubiquity and theoretical importance of these conditional behaviors in the regulation of ecological interactions involving predators, competitors, and mates, virtually nothing is known about how the social environment affects their expression and evolution, especially in marine organisms. This research project will test and extend the basic predictions of social evolutionary theory using a group of colonial marine cnidarians (the hydractiniids) that exhibit dramatic, context-dependent behaviors, including intergenotypic fusion (and chimera formation) and aggression, and that experience a broad range of social environments. By examining from ecological, genetic, and phylogenetic perspectives how selection mediated by the social environment influences the expression and evolution of fusion and aggression in this behaviorally and socially diverse group of hydrozoans, this research will build a general foundation for understanding the evolution of conditional behaviors, the cues underlying their expression, and their widespread effects at the level of the population and community.