Abstract
Hybrid zones are, roughly speaking, narrow regions in which genetically
distinctpopulationsmeet, mate, andproducehybrids.They areoften only a few
hundred meterswide andyet may be severalhundred kilometerslong. They are
found in a wide varietyof organisms:Tables 1 and 2 list about 150 reasonably
clear examples, in which there is a spatialtransitionbetween two hybridizing
forms. Such a widespreadandstrikingphenomenonrequiresexplanation; more
importantly, offers us severalways of understanding natureand origin of
it the
species. First, hybridzones pose interestingquestions for the taxonomist, for
they contrasttwo views of the species: as a set of populations delimited by
genetic barriersto gene exchange; and as a set of populationsmaintainedin a
particular stableequilibrium selection. Second, the wide rangeof genotypes
by
found in a hybrid zone can be used to analyze the genetic differences and
selective forces thatseparate taxainvolved. This may allow some inferences
the
aboutthe way these differencesevolved and, by extrapolation,aboutthe way
fully isolated species diverge from each other. Finally, models of parapatric
speciation, and of Wright's "shiftingbalance," involve the formation, move-
ment, and modification of hybrid zones. Hybrid zones must be understood
before the plausibility of these models can be judged.
Description
Analysis of Hybrid Zones
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