Differentiation of ancestral populations and hybrid intermediacy. Invasive sculpins separate from all stream sculpins along the first CV axis. Sculpin populations from Stream Broel and Stream Naaf separate along the second CV axis. BI hybrids form an intermediate group between their parental populations. Distance based assignment based on these two axes correctly identifies pure candidates while a majority of BI hybrids are wrongly assigned to one of the parental groups with which they overlap.