Scrutinizing a Superspecies: Patterns of Gene Flow among Common, Long-legged and Upland Buzzard

Genetic study explores population structure of Palearctic Buzzards.

“That is clearly a honey buzzard (Pernis apivorus),” says the raptor expert while I squint my eyes to find a little black dot barely visible against a white cloud. I am always amazed at how some birdwatchers can recognize raptor species by their silhouette. Of course there are some obvious ones, such as the red kite (Milvus milvus) with its forked tail. But can you tell the difference between a common buzzard (Buteo buteo) and a long-legged buzzard (Buteo rufinus) when they soar up high? A recent paper in the journal Molecular Phylogenetics and Evolution shows that they are also genetically difficult to tell apart.

buzzard silhouette.jpg

Silhouettes of common buzzard and long-legged buzzard. Can you tell which is which?

 

Superspecies

The taxonomy of Palearctic buzzards (genus Buteo) is – to put it mildly – challenging. Several ornithologists have tried to create order in the subspecific chaos of this species complex. The failure to achieve this has been attributed to extensive gene flow between the different (sub)species. Therefore, common buzzard is often treated as a superspecies, comprised of several allospecies. Here is a recent classification proposed by Luise Kruckenhauser et al. (2004)

classification buteo.jpg

A classification for the genus Buteo (from: Kruckenhauser et al. (2004) Zoologica Scripta)

 

Three species and three markers types

Michael Jowers (University of Porto) and his colleagues decided to focus on three members of this superspecies: the common buzzard, the long-legged buzzard and the Upland buzzard (B. hemilasius). They collected samples across the range of these species and sequenced three types of markers: mitochondrial DNA, nuclear markers and microsatellites. Together these genetic markers provide a window on the recent history of the three buzzard species.  Let’s look at the results one marker type at a time.

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Common Buzzard in Belgium © Jente Ottenburghs

 

Mitochondrial Clusters and a Nuclear Mess

The mitochondrial markers differentiated between the species and agreed with the taxonomic classification. The Upland buzzard is clearly distinct from the other buzzards. The situation of common buzzard and long-legged buzzard is a bit more complicated. One subspecies of the long-legged buzzard (rufinus) forms a separate cluster whereas another subspecies (cirtensis, also known as Atlas long-legged buzzard) groups with two subspecies of the common buzzards (buteo and vulpinus). The clustering of cirtensis with common buzzard might be due to hybridization. In recent years, hybrids have been reported in Tunisia and the Strait of Gibraltar.

I can be short about the nuclear markers: everything is mixed. There is no clear clustering of particular subspecies or even species. This pattern is probably due to a combination of gene flow and the recent origin of the buzzard taxa.

network-buzzards

Mitochondrial haplotype network for three buzzard species. The Upland buzzard (dark blue) is clearly distinct from the others. One subspecies of long-legged buzzard (rufinus, light blue) is separate while another subspecies (cirensis, green) clusters with two subspecies of the common buzzard: buteo (red) and vulpinus (orange). From: Jowers et al. 2019 MPE.

 

More Gene Flow?

The microsatellites, finally, uncovered three clusters that correspond to the three species in this study. There were, however, signs of gene flow between the different clusters. Individuals from contact zones between particular species showed admixed genomes. In accordance with the mitochondrial network, there is probably gene flow between Atlas long-legged buzzard and common buzzard. Moreover, long-legged buzzard has also been exchanging genetic material with Upland buzzard. Indeed, hybrids between these species have been documented in central Asia.

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Long-legged buzzard (from: http://www.ebird.com/)

 

Speciation in Progress

These analyses reveal the taxonomic difficulties of Palearctic buzzards and indicate that the speciation process is still ongoing (and might never be complete). Speciation is a continuous process that prevents taxonomists from pigeonholing populations. Buzzards are a clear example of this.

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Upland buzzard (from: http://www.hbw.com/)

 

References

Jowers, M.J., Sánchez-Ramírez, S., Lopes, S., Karyakin, I., Dombrovski, V., Qninba, A., Valkenburg, T., Onofre, N., Ferrand, N., Beja, P., Palma, L. & Godinho, R. (2019) Unravelling population processes over the Late Pleistocene driving contemporary genetic divergence in Palearctic buzzards. Molecular Phylogenetics and Evolution, 134:269-281.

 

This paper has been added to the Accipitriformes page.

2 thoughts on “Scrutinizing a Superspecies: Patterns of Gene Flow among Common, Long-legged and Upland Buzzard

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