secondary intergradation

secondary intergradation

a zone of hybridization in which two previously separated populations have come together and interbred.
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The origin of clinal variation in natural populations has been debated since Mayr (1942 in Yang and Yeh 1995) postulated a differentiation between zones of primary and secondary intergradation. Mayr defined primary intergradation as clinal variation that develops within a continuous series of populations and secondary intergradation as the consequence of junction between populations that have become differentiated in allopatry.
Rather, this high divergence suggests that the Iberian Peninsula is an area of secondary intergradation between two deeply diverged branches (Smith et al.
The hypothesis of secondary intergradation was developed to explain the Spanish ratio cline between M and A haplotypes, which are highly divergent (ca.
The existence of an extended clinal variation for morphological characters had prompted the hypothesis of primary intergradation and was congruent with the hypothesis of secondary intergradation. These morphological clines extend from the equator to the Polar Circle, that is, over distances that are much larger than the formerly postulated transition/contact zone.
Raymond & Hardy (1983) believed this variability to suggest secondary intergradation. In general, the specimens of E.
The origin of clinal variation in natural populations has been debated since Mayr (1942) postulated a differentiation between zones of primary and secondary intergradation. Mayr defined primary intergradation as clinal variation that develops within a continuous series of populations and secondary intergradation as the consequence of junction between populations that have become differentiated in allopatry.
As climatic and ecological variables change only gradually along this cline (Espenshade 1964; Cohen 1973), a sharp discontinuity dividing populations into northern and southern groups would suggest secondary intergradation. Such a pattern combined with evidence of restricted gene flow within transitional populations would support specific status for the North Carolina type.

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