Hybrid Origins of Plant Species

Abstract

▪ Abstract The origin of new homoploid species via hybridization is theoretically difficult because it requires the development of reproductive isolation in sympatry. Nonetheless, this mode is often and carelessly used by botanists to account for the formation of species that are morphologically intermediate with respect to related congeners. Here, I review experimental, theoretical, and empirical studies of homoploid hybrid speciation to evaluate the feasibility, tempo, and frequency of this mode. Theoretical models, simulation studies, and experimental syntheses of stabilized hybrid neospecies indicate that it is feasible, although evolutionary conditions are stringent. Hybrid speciation appears to be promoted by rapid chromosomal evolution and the availability of a suitable hybrid habitat. A selfing breeding system may enhance establishment of hybrid species, but this advantage appears to be counterbalanced by lower rates of natural hybridization among selfing taxa. Simulation studies and crossing expe...