Research to be published in the journal Molecular Phylogenetics and Evolution has shown that genetic analysis does not support the treatment of Balearic and Yelkouan Shearwaters as separate species.
The taxonomy of North Atlantic and Mediterranean shearwaters in the genus Puffinus has been a controversial subject for decades. Until the end of the 1980s, checklists included only one medium-sized species in the region, with Manx Shearwater Puffinus puffinus including the subspecies P p mauretanicus and P p yelkouan.
The treatment of Yelkouan Shearwater (pictured) and Balearic Shearwater as separate species has never been universally adopted (Natalino Fenech).
The species was then split into Manx and 'Mediterranean Shearwater', which comprised mauretanicus and yelkouan. These were in turn split into Balearic Shearwater and Yelkouan Shearwater respectively, following taxonomic recommendations at the turn of the century, though this approach was never adopted by the Howard and Moore checklist.
The team led by Joan Ferrer Obiol of the University of Barcelona sent DNA extracts from 42 shearwaters of the eight North Atlantic and Mediterranean Puffinus species and subspecies to the University of Texas for detailed and varied analysis, alongside a review of morphological, behavioural and ecological evidence. The work was set against the application of several different approaches to species delimitation.
It was revealed by fineRADstructure analyses that Balearic and Yelkouan Shearwaters, rather than being diverged species, are on the cusp of beginning speciation. This was supported by phylogenetic analysis, which showed the two taxa are currently diverging.
Results showed that Balearic Shearwater (pictured) and Yelkouan Shearwater are only just beginning to evolve into different species (Richard Stonier).
The recently described Canary Islands subspecies of Manx Shearwater P p canariensis showed higher genetic differentiation from the nominate form of that species than there was between mauretanicus and yelkouan, which were the least differentiated taxa analysed.
The fineRADstructure analysis of Barolo, Boyd's and Audubon's Shearwaters supported their treatment as separate species. Divergence dating analyses placed the split between the West Atlantic clade (lherminieri) and the East Atlantic clade (boydi and baroli) at approximately 1 million years ago, with the divergence between boydi and baroli occurring approximately 120,000 years ago.
Comparison of the genomes of mauretanicus and yelkouan showed no fixed differences, only allele frequency differences. However, fine-scale population structure analysis was at least able to support the treatment of yelkouan and mauretanicus as two distinct groups.
The authors propose a return to late 20th century treatment of mauretanicus and yelkouan as subspecies of Mediterranean Shearwater Puffinus yelkouan. They emphasised that despite the evidence pointing towards lumping the two taxa as one species again, this should not influence conservation action in a negative way, as both forms are still 'evolutionary significant units'.
Currently, Balearic Shearwater is listed as Critically Endangered by the IUCN, while Yelkouan Shearwater is categorised as Vulnerable. Both taxa are at risk due to longline fishing bycatch in the Mediterranean.
They argued that the fine-scale population structure revealed by the study should be used to protect the birds, offering advanced detail compared to previous approaches in order to identify more precise origins of victims of bycatch.
Reference
Obiol, J F et al. 2022. Species delimitation using genomic data to resolve taxonomic uncertainties in a speciation continuum of pelagic seabirds. Molecular Phylogenetics and Evolution. DOI: https://doi.org/10.1016/j.ympev.2022.107671
