Hybridization and backcrossing between the endangered brown shrike (Lanius cristatus superciliosus) and the common bull-headed shrike (L. bucephalus bucephalus)

Abstract

Abstract Interspecific hybridization has long been of interest to biologists due to its implications for species concepts, gene flow, and conservation. We found a putative hybrid between the endangered brown shrike (Lanius cristatus superciliosus) and the common bull-headed shrike (Lanius bucephalus) at the foot of Mt. Fuji, central Japan, where the adult sex ratio of brown shrikes is biased towards the male. Brown and bull-headed shrikes are closely related, and their hybridization is critical for the survival and conservation of the brown shrike. We tried to identify this individual based on genetic, morphological, plumage, and acoustic analysis. The hybrid had intermediate genetic, morphological, and plumage features between the two parental species. The maternal lineage of the hybrid was suggested to be the bull-headed shrike by COI analysis. We thus conclude that the hybrid resulted from interbreeding between a male brown shrike and a female bull-headed shrike, and a skewed sex ratio in the brown shrike may have contributed to this hybridization. Skewed sex ratio is a useful indicator of population viability and knowledge of this is helpful in rare species conservation. Genetic introgression between brown and bull-headed shrikes cannot be denied because the hybrid individual was fertile and backcrossing occurred. Exploring past and ongoing genetic relationships of the shrikes has led to insights into the evolutionary background and the potential of hybridization in an evolutionary context.