MODELS OF SYMBIOSIS

A tentative outline of concepts is proposed for the evolutionary genet ics of symbiosis. There are three main topics. The first concerns the tension between the integrative and disruptive forces of kin selection . Kin selection can be disruptive because competition among close rela tives favors dispersal and a reduction in relatedness among neighbors. Kin selection acts independently within each species of a symbiotic c ommunity but has important consequences for the integration of the com munity into a cooperative unit. The second topic describes the evoluti on of beneficial, synergistic effects between species, The evolution o f mutual effects depends on various correlations between species, Gene tic correlations are analogous to linkage disequilibrium in standard M endelian genetics. Correlations in reproductive success between symbio tic partners arise from codispersal and reproductive synchrony. The th ird topic concerns the evolution of asymmetrical symbioses in which on e species can dominate its partner. Dominance may explain the evolutio n of uniparental inheritance among cytoplasmic symbionts and a peculia r form of germ-soma separation in the symbionts of insects.