XVI International Botanical Congess

Botanists often view hybridization as contributing to adaptive evolution while zoologists generally consider hybridization as testing the efficacy of species isolating barriers. Recent reviews by botanists also reveal other fundamental differences in viewpoint concerning the fitness of hybrids relative to their parents and the role ofexogenous selection in maintaining hybrid zones. We add to this important area of speciation biology by stressing the need to examine hybridization within a genetic framework. A review of the literature demonstrates the importance of both selection against hybrids and exogenous selection in the maintenance of hybrid zones. We discuss ways in which particularly fit recombinant genotypes may be able to escape, even when hybrids are on average less fit, and so contribute to hybrid speciation. We illustrate these concepts with one and two locus population genetic models which emphasize the roles of gene interaction, recombination and random drift in hybrid speciation. We conclude with a call for research programs that incorporate genetic methodologies to enhance our understanding of hybridization in evolution.