Genetic study finds few admixed individuals in the contact zone.
Today I learned a new word: yaffling. It refers to the sound a Eurasian Green Woodpecker (Picus viridis) makes when it flies off (click here to listen to it). I have heard this loud “laughter” during countless forest walks. Indeed, this distinctive call echoes throughout most of the European forests because this species occurs from northern Sweden all the way down to southern France. When you cross the Pyrenees into Spain, however, you will meet another woodpecker species – the Iberian Green Woodpecker (P. sharpei) – that produces a similar call. A recent study in the Journal of Ornithology explored a contact zone between these two woodpeckers.
Le Pic Vert
The Iberian and Eurasian Green Woodpecker might sound alike, they differ by several plumage features. The color of the face is most obvious: the Iberian birds have a grey face whereas the face is black in Eurasian woodpeckers. In the Pyrenees, which we crossed in the introduction of the blog post, individuals with intermediate plumage have been observed. Already in the 1920s, Jouard asked if there was “une nouvelle forme de Pic Vert” in the Pyrenees (For my non-French-speaking readers: a new form of Green Woodpecker).
No Gene Flow
This observation, along with more recent ones, suggests that there is a hybrid zone between these Woodpeckers. Jean-Marc Pons and his colleagues collected samples within and outside the putative contact zone. Based on a suite of 19 molecular markers, they characterized the genetic structure in this region. They found “no introgression of nuclear loci in allopatric populations located on both sides of the contact zone, which thus acts as an efficient barrier to gene flow.” This finding contributes to the idea that Eurasian and Iberian Green Woodpecker are distinct species.
In the contact zone, the researchers found several individuals that carried DNA from both species. This indicates that although hybridization occurs, the genes are not flowing between the species. There is probably some selection against hybrids. Based on these findings, the contact zone is most likely a so-called tension zone. This particular type of contact zone occurs when the effects of dispersal of parental species into the zone and selection against hybrids balance each other.
Cline analyses revealed that the hybrid zone is about 245 kilometers wide and centered in the area between Béziers and Montpellier (for more on cline theory, you can read this blog post). This seems like the perfect place for a hybrid zone, given that the University of Montpellier is known for its excellent evolutionary research.
Pons, J. M., Masson, C., Olioso, G., & Fuchs, J. (2019). Gene flow and genetic admixture across a secondary contact zone between two divergent lineages of the Eurasian Green Woodpecker Picus viridis. Journal of Ornithology, 1-11.
This paper has been added to the Piciformes page.