Hybridization, introgression, and the nature of species boundaries.
Species can be defined as populations that are diagnosably distinct, reproductively isolated, cohesive, or exclusive groups of organisms. Boundaries between species in sympatry are maintained by intrinsic barriers to gene exchange; these boundaries may not be uniform in space, in time, or across the genome. Here, we explore the nature of the species boundary, defined as the phenotypes/genes/genome regions that remain differentiated in the face of potential hybridization and introgression. We emphasize that species boundaries are semipermeable, with permeability (gene exchange) being a function of genome region. The early evidence for semipermeable species boundaries came from data on differential introgression in hybrid zones. This "genic view" of species was common in the hybrid zone literature even when few molecular markers were available to characterize genome-wide patterns of variation. Now, molecular tools allow detailed characterization of differentiation between diverging lineages and patterns of variation across natural hybrid zones, but the questions being asked by evolutionary biologists have remained much the same. Recent data (from DNA sequences and genotypes) reinforce earlier conclusions about the semipermeable nature of most species boundaries. However, debate persists over the nature and extent of genome divergence that accompanies speciation.
['Harrison|Richard G|RG|', 'Larson|Erica L|EL|']
D000222:Adaptation, Physiological D000818:Animals D000829:Animals, Domestic D002678:Chimera D018556:Crops, Agricultural D049810:Genetic Speciation D005828:Genetics, Population D016678:Genome D006801:Humans D006824:Hybridization, Genetic D020412:Multifactorial Inheritance D060047:Reproductive Isolation
reproductive isolation hybrid zones genomic divergence speciation