Still, there is very little intergradation in the areas where subspecies meet.

In some regions, there are areas of intergradation with other subspecies.

The distribution of the two are known to approach each other, but there is no evidence of intergradation.

Intergradation does not occur between these two forms.

Here too is a broad zone of intergradation.

Intergradation between the two subspecies occurs in the lower Tennessee River unit.

There are two subspecies, with extensive intergradation where their ranges contact:

In some cases, intergradation may occur.

A zone of intergradation occurs between the two subspecies in north-central Queensland.

Individuals showing intermediate features are known from the small area of contact in north-central Brazil, but intergradation between the two species is generally limited.

There are two types of intergradation:

Intergradation between the subspecies does occur.

If there is little intergradation in this region, the case for the southern Andean populations being a distinct species is rather robust.

Such a broad area of intergradation has been taken as evidence of substantial genetic exchange between the two taxa.

The gradual variation over geographic range and extensive intergradation means that acceptance of the various subspecies varies between authorities.

Wide intergradation with P. o. gibraltariensis and treated as a synonym of it by many authorities.

Primary intergradation:

Secondary intergradation:

Clench (1947) discounted the idea of imbricata being a separate variety at all because of the complete intergradation he saw between the forms.

At some localities individuals with intermediate features are commonly seen, but at others the two morphs seemingly co-occur without signs of intergradation.

In zoology, intergradation is the way in which two distinct subspecies are connected via areas where populations are found that have the characteristics of both.

Intergradation with A. p. leucostoma occurs east of Mobile Bay, Alabama, and slightly further east from there.

There are two subspecies which are not very distinct and almost form a continuous cline, with an extensive intergradation zone in northern Peru:

This taxon is a subspecies of Achatinella viridans as there is a complete intergradation between them.

Birds in eastern Chad (E. striolata jebelmarrae) show some evidence of intergradation with House Bunting.