Adventures in the Andes: The Tantalizing Tale of the Torrent Duck

Molecular and morphological analyses uncover three distinct lineages in the Torrent Duck.

The Torrent Duck (Merganetta armata) surely lives up to its name. These beautiful ducks – the males have a striking black and white head and a fire-red bill – fearlessly dive into the rapid waters of the Andes. They have a wide distribution, ranging from southern Chile all the way up to Venezuela. Their widespread occurrence and affinity for wild waters raises an important question: How do the Andean river networks shape the population structure of this species? On the one hand, rivers could promote dispersal and gene flow between distant populations. On the other hand, rivers could act as barriers to gene flow, leading to population differentiation. A recent study in the journal Zoologica Scripta tackled this question and assessed the population structure of this widespread species.

 

Three Groups

Natalia Gutiérrez-Pinto and her colleagues analyzed the mitochondrial control region of 198 Torrent Ducks. These analyses uncovered three distinct lineages that correspond to previously described subspecies. A Northern Andes group (colombiana) with birds from Colombia, Ecuador, and northern Peru. A Central Andes group (leucogenis) that covers Peru and northwestern Bolivia. And a Southern Andes group (armata) with individuals living in southeastern Bolivia and Argentina.

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Analyses of the mitochondrial control region uncovered three distinct lineages that correspond to previously described subspecies of the Torrent Duck. From: Gutiérrez-Pinto et al. (2019) Zoologica Scripta

 

Barriers

The distribution of these three groups seems to match the geographic regions delineated by Jon Fjeldså: Páramo, Puna and Southern Andes. The main geographical barriers between these regions are the North Peruvian Low (between Páramo and Puna) and the Bolivian Altiplano (between Puna and Southern Andes). In case of the Torrent Ducks, the Bolivian Altiplano appears to be an effective barriers between the Central and Southern Andes groups. The high elevations of the Tunari mountain range separate both groups.

The role of North Peruvian Low, however, is less clear. This region was not densely sampled in the study, preventing the researchers from assessing potential gene flow across this barrier. Moreover, the North Peruvian Low has a complex topography which might provide Torrent Ducks with small watersheds that connect the Northern with the Central Andes group. More research in this area is needed to characterize this barrier.

Merganetta_armata

A pair of Torrent Ducks in Colombia © Alejandro Bayer Tamayo | Wikimedia Commons

 

Morphology

As mentioned above, the three mitochondrial lineages correspond to three previously described subspecies. A morphological analysis of these birds showed that the Northern Andes group (colombiana) is highly differentiation from the other two groups. The differences between the Central (leucogenis) and the Southern (armata) groups are more subtle. Possibly, these birds represent the extremes of a range of phenotypes. There might even be a hybrid zone at some location. Denser sampling is required to figure this out. If it turns out that they hybridize, you will definitely read it on this blog.

 

References

Gutiérrez‐Pinto, N., McCracken, K. G., Tubaro, P., Kopuchian, C., Astie, A., & Cadena, C. D. (2019). Molecular and morphological differentiation among Torrent Duck (Merganetta armata) populations in the Andes. Zoologica Scripta.

 

This paper has been added to the Anseriformes page.

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