Symbiotic sympatric speciation: consequence of interaction-driven phenotype differentiation through developmental plasticity

 A mechanism of sympatric speciation is presented based on the interaction-induced developmental plasticity of phenotypes. First, phenotypes of individuals with identical genotypes split into a few groups, according to instability in the developmental dynamics that are triggered with the competitive interaction among individuals. Then, through mutational changes in the genes, the phenotypic differences are fixed to genes, until the groups are completely separated in genotype as well as phenotype. It is also demonstrated that the proposed theory leads to hybrid sterility under sexual recombination, and thus speciation is completed in the sense of reproductive isolation. As a result of this postmating isolation, the mating preference evolves later. When there are two alleles, the correlation between alleles is formed to consolidate speciation. When individuals are located apart in space, different species are later segregated spatially, implying that the speciation so far regarded to be allopatric may be a result of sympatric speciation. Relationships to previous theories, frequency-dependent selection, reinforcement, Baldwin's effect, phenotypic plasticity, and resource competition are briefly discussed. Relevance of the results to natural evolution is discussed, including punctuated equilibrium, incomplete penetrance in mutants, and the change in flexibility in genotype–phenotype correspondence. Finally, we discuss how our theory is confirmed both in the field and in the laboratory, in an experiment using Escherichia coli. Received: January 30, 2002 / Accepted: May 13, 2002