When individuals from two different species interbreed, hybrid organisms may emerge that display characteristics from both genetic lineages. While hybridization is a common natural phenomenon, it is often seen as a challenge in biodiversity conservation. Now, a study published in the journal Proceedings of the National Academy of Sciences ( PNAS ) reveals that hybridization between the Mediterranean shearwater and the Balearic shearwater - a seabird at critical risk of extinction - has been decisive in maintaining genetic diversity and facilitating the survival of the most threatened seabird in Europe.
With doctoral student Guillem Izquierdo-Arànega as the main driving force, the research was led by professors Julio Rozas, Marta Riutort and Jacob González-Solís from the Faculty of Biology and the Biodiversity Research Institute of the University of Barcelona (IRBio), along with Joan Ferrer Obiol from the University of Milan (Italy). Cristian Cuevas-Caballé, recently awarded his PhD at the UB, is also a co-author of the article, along with other experts.
The new research emphasizes that hybridization should be considered in conservation and management plans, especially at a time when human pressure on biodiversity is accelerating the decline and extinction of life forms across the planet. In the specific case of shearwaters, there is also an urgent need to reduce the accidental bycatch of seabirds in fishing gear to prevent the future extinction of these iconic species.
The Balearic shearwater: an extinction foretold?
The Balearic shearwater (Puffinus mauretanicus), a taxon endemic to the Balearic Islands, is critically endangered according to the International Union for Conservation of Nature (IUCN). Its breeding area is limited to the Balearic Islands, it has a low reproductive rate, and suffers high additional mortality due to accidental bycatch in longline fisheries. Several simulations suggest that it could become extinct in the coming decades if urgent action is not taken.
The new study investigates the dynamics of hybridization between the Balearic shearwater and the Mediterranean shearwater (Puffinus yelkouan) and its effect on the genomic diversity of the Balearic shearwater - a poorly studied issue that has limited conservation strategies. These two genetically close lineages have undergone recurrent episodes of divergence and hybridization during the Pleistocene glacial cycles, creating a geographical gradient of hybridization and genetic differentiation from the Eastern Mediterranean to the Pityusic Islands (Ibiza and Formentera). The study also finds that the Menorca population is genetically closer to the yelkouan lineage than to the mauretanicus.
