Puffin population structure: There is more than meets the eye

Genetic study provides evidence for four genetic clusters.

Who doesn’t like Atlantic Puffins (Fratercula arctica)? Small black-and-white seabirds with colorful beaks that nest in rabbit-hole-like burrows. It sounds like something out of a fairytale. But these iconic birds do exist and I have had the pleasure of observing one in close proximity. On a holiday in Wales with my father and some friends, we were planning to visit a breeding colony on a nearby island. Due to the bad weather, however, the boat trip was cancelled and we were forced to change our plans. Walking along the Welsh shores, we suddenly discovered a stranded Puffin. This bird was exhausted, but still managed to bite my fathers finger. We brought it (the Puffin, not my fathers finger) to a nearby house where the surprised owner promised to deliver it at an animal shelter. We never knew if he did and what happened to this particular Puffin.

Despite their attractive looks and endangered status, little genetic work has been done on Puffins. Their current taxonomy is largely based on size differences:

  • F. a. grabae: the smallest subspecies in France, Britain, Ireland and southern Iceland
  • F. a. arctica: the intermediate subspecies in Norway, Iceland and Canada
  • F. a. naumanni: the largest subspecies in the high Arctic (e.g., Spitsbergen, Greenland, northern Canada)

A recent study in the journal Communications Biology provided a genomic perspective on this seabird species. Are these subspecies also supported by genetic data?

Four Clusters

Oliver Kersten and his colleagues compared the genetic make-up of 71 birds to detect any population structure. They could delineate four main clusters. The Puffins from Spitsbergen were clearly distinct from the other populations. And there were more subtle differences between birds from Canada, the Isle of May and multiple colonies from Iceland/Norway/Faroe Islands. Interestingly, these four genetic groups do not correspond to the three subspecies described above:

Although the genetically distinct Spitsbergen cluster coincides with the classification of morphologically large puffins in the High Arctic (F. a. naumanni), we observe gene flow from Spitsbergen into Bjørnøya, which has been considered F. a. arctica. Furthermore, the geographic divide between F. a. grabae and F. a. arctica lies farther south than previously thought, with the Faroese puffins being genetically closer to F. a. arctica than to F. a. grabae.

Moreover, the genetic population structure in the nuclear data was not observed in the mitochondrial DNA (mtDNA). The lack of clear population differentiation in mtDNA could be due to recent population expansions (but see also the seabird paradox). More detailed demographic analyses are needed to unravel the evolutionary history of the Atlantic Puffin.

The genomic data pointed to four genetic clusters (see figures c and d). This population structure was not visible in the mitochondrial DNA (figure b), suggesting a recent population expansion. From: Kersten et al. (2021).

Hybrid Population

In the quote above, you could already read that the researchers found “gene flow from Spitsbergen into Bjørnøya”. For readers unfamiliar with islands in the Arctic: Bjørnøya is a small island between Spitsbergen and Norway that houses less than 1000 breeding pairs. Although the Spitsbergen population is clearly differentiated from the other populations, it still contributes to the formation of a hybrid population on Bjørnøya. An interesting case of secondary contact that requires further investigation.

In summary, a genomic exploration of the Atlantic Puffin uncovered four distinct genetic clusters and a region of secondary contact on the small island of Bjørnøya. I wonder where the Welsh Puffin we found on holiday fits in…

References

Kersten, O., Star, B., Leigh, D. M., Anker-Nilssen, T., Strøm, H., Danielsen, J., … & Boessenkool, S. (2021). Complex population structure of the Atlantic puffin revealed by whole genome analyses. Communications Biology4(1), 1-12.

Featured image: Atlantic Puffin (Fratercula arctica) © Charles J. Sharp | Wikimedia Commons

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