In
zoology, intergradation is the way in which two distinct
subspecies
In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
are connected via areas where
populations are found that have the characteristics of both. There are two types of intergradation: primary and secondary intergradation.
Primary intergradation
This occurs in cases where two subspecies are connected via one or more intermediate populations, each of which is in turn intermediate to its adjacent populations and exhibits more or less the same amount of
variability as any other population within the
species. Adjacent populations and subspecies are subject to
cline intergradation, and in these situations it is usually taken for granted that the clines are causally related (by
natural selection) to
environmental gradients.
[Mayr E, Ashlock PD (1991). ''Principles of Systematic Zoology''. Second edition. McGraw-Hill. .]
Secondary intergradation
When contact between a geographically isolated subspecies is reestablished with the main body of the species or with another isolate subspecies, interbreeding takes place as long as the isolate has not yet evolved an effective set of isolating mechanisms. Consequently, a relatively distinct zone or belt of
hybridization
Hybridization (or hybridisation) may refer to:
*Hybridization (biology), the process of combining different varieties of organisms to create a hybrid
*Orbital hybridization, in chemistry, the mixing of atomic orbitals into new hybrid orbitals
*Nu ...
will develop depending on the degree of
genetic and
phenotypic difference that was achieved by the previously isolated
subspecies
In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
.
See also
*
Ring species
References
{{Reflist
Hybridisation (biology)
Population genetics
Evolutionary biology