Evolution of discriminatory aggression in marine invertebrates

Many species of sessile marine organisms show allotype-conditional aggression towards conspecifics. However, a recent theoretical analysis (Grosberg & Quinn, 1989, Evolution 43, 504-515.) was unable to find conditions permitting a discriminatory ESS against unconditionally aggressive or non-aggressive strategies. This study shows that discrimination can be an ESS if animals interact with clonemates more frequently than randomly as occurs when animals reproduce by budding of fission. This agrees well with the observation that clonal sea anemones are usually discriminators and solitary species usually non-aggressive to conspecifics (Francis, 1988, Biol. Bull. 174, 241-253.) In addition, discrimination can be an ESS if discriminators retaliate against unconditionally aggressive conspecifics of the same allotype, or if the payoff to two sharers of a resource is greater than the payoff to both when sharing does not occur.