Natural hybridization with invasive bleak Alburnus alburnus threatens the survival of Iberian endemic calandino Squalius alburnoides complex and Southern Iberian chub Squalius pyrenaicus

Abstract

Hybrids of invasive bleak Alburnus alburnus and native endemic calandino Squalius alburnoides complex and Southern Iberian chub Squalius pyrenaicus were found in the River Jarama (Tagus River basin, central Spain). Morphological analyses show that hybrids are intermediate in shape between the parent species. Molecular mitochondrial and nuclear analyses evidence that hybridization was different in terms of the direction of gene introgression, with hybrids ♀ A. alburnus × ♂ S. pyrenaicus and ♀ S. alburnoides complex × ♂ A. alburnus. As far as we know, this is the first evidence of interspecific hybridization between a fish hybrid complex and an invasive exotic fish. The hybridization occurred at least during 3 years in a short time period after the arrival of exotic bleak. The spread of bleak in the Iberian Peninsula can be a serious threat for the survival of endemic Squalius species, as well as other close Leuciscinae such as the endangered jarabugo Anaecypris hispanica.