Bimodal hybrid zones and speciation

Contact zones exemplify a series of stages in speciation, In unimodal hybri d zones intermediates predominate; in bimodal zones hybrids are rare and pa rental forms predominate; and finally, species might overlap, but never hyb ridize. Recent studies show bimodality to be associated strongly with assor tative mating or fertilization, and only weakly with overall levels of gene tic divergence or intrinsic genomic incompatibility. Ecological divergence across most bimodal hybrid zones suggests that ecology contributes more to speciation than genomic incompatibility. This continuum of stable contact z ones provides empirical evidence for a route to speciation. which does not require allopatry.