Wiktionary
intergrade
vb. To pass or change from one state to another by steps or stages.
Usage examples of "intergrade".
The great timber wolf of the central and northern chains of the Rockies and coast ranges is in every way a more formidable creature than the buffalo wolf of the plains, although they intergrade.
The Camargue, channels and hummocks, tasselled rushes where salt sea and mountain creek intergraded in a balance that shifted with the seasons, with ebb of tide and springtime spate.
They form a slight variety of what was formerly the ordinary plains bison, intergrading with it.