Data from: Species integrity enhanced by a predation cost to hybrids in the wild

Species integrity can be challenged, and even eroded, if closely related
species can hybridize and produce fertile offspring of comparable fitness
to that of parental species. The maintenance of newly diverged or closely
related species therefore hinges on the establishment and effectiveness of
pre- and/or post-zygotic reproductive barriers. Ecological selection,
including predation, is often presumed to contribute to reduced hybrid
fitness, but field evidence for a predation cost to hybridization remains
elusive. Here we provide proof-of-concept for predation on hybrids being a
postzygotic barrier to gene flow in the wild. Cyprinid fishes commonly
produce fertile, viable hybrid offspring and therefore make excellent
study organisms to investigate ecological costs to hybrids. We
electronically tagged two freshwater cyprinid fish species (roach Rutilus
rutilus and bream Abramis brama) and their hybrids in 2005. Tagged fish
were returned to their lake of origin, exposing them to natural predation
risk from apex avian predators (great cormorant, Phalacrocorax carbo).
Scanning for regurgitated tags under cormorant roosts 3–4 years later
identified cormorant-killed individual fish and allowed us to directly
test for a predation cost to hybrids in the wild. Hybrid individuals were
found significantly more susceptible to cormorant predation than
individuals from either parental species. Such ecological selection
against hybrids contributes to species integrity, and can enhance species
diversification.