Hybridization —the crossing between different species— has long been considered a threat to conservation, as it could dilute unique evolutionary lineages. However, an increasing number of studies show that this process can also play a positive role, bringing genetic variability and increasing the adaptive potential of threatened species.
A study published in Proceedings of the National Academy of Sciences (PNAS), led by the University of Barcelona with the prominent participation of members of the Catalan Biogenome Project (CBP), shows that the Balearic shearwater (Puffinus mauretanicus) —a seabird endemic to the Balearic Islands and listed as Critically Endangered— has maintained its genetic diversity thanks to recurrent episodes of hybridization with its sister species, the Yelkouan shearwater (Puffinus yelkouan).
A complex history of divergence and hybridization
The team reconstructed the demographic history of the two species and found that, while during glacial periods they remained isolated, in interglacial phases there were widespread hybridization events. This gene flow has been particularly relevant in contact zones such as Menorca and Cabrera, where both species coexist.
The results reveal that genetic introgression has facilitated the exchange of adaptive haplotypes, including genomic regions linked to differences in migratory strategies. Moreover, populations of Balearic shearwaters show no signs of inbreeding despite their decline, a fact attributed to the pervasiveness of hybridization with the Yelkouan shearwater.
The role of the CBP: genomes for conservation
This advance would not have been possible without the first reference genome of the Balearic shearwater, which was sequenced and annotated in the laboratories of Julio Rozas and Marta Riutort (UB-IRBio) as part of the Catalan Biogenome Project (CBP), a project promoted by the Institut d’Estudis Catalans (IEC).
As Marta Riutort, co-chair of the project, points out:
“This study demonstrates that reference genomes are essential tools for understanding evolutionary processes and applying them to conservation. The case of the Balearic shearwater is a clear example of how genomics allows us to identify gene flow, reconstruct past history, and predict future survival scenarios.”
Conservation: beyond genetics
The team’s simulations indicate that protecting hybrid colonies could safeguard the genetic diversity of the Balearic shearwater in the face of future demographic bottlenecks. Nevertheless, researchers stress that the top priority remains reducing mortality caused by accidental bycatch in fishing gear, which is currently the main threat to the species.
This study not only provides new tools for biodiversity management, but also reinforces the mission of the Catalan Biogenome Project: to generate reference genomes for species across the Catalan-speaking territories and place them at the service of science and conservation.
Article in PNAS: Izquierdo-Arànega, G. et al. “Pervasive and recurrent hybridisation prevents inbreeding depression in Europe’s most threatened seabird”