05/10/2019
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Torrent Duck: one species or three?

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With a wide distribution on Andean rivers from Venezuela to southern Chile, Torrent Duck Merganetta armata is generally treated as a single species comprising three to six subspecies. The subspecies list below represents the congruent views of IOC (worldbirdnames.org), Clements, and Birdlife/HBW taxonomies: 

  • M a colombiana – Venezuela S to N Ecuador;
  • M a leucogenis – C Ecuador to C Peru;
  • M a turneri – S Peru and extreme N Chile (N Tarapacá);
  • M a garleppi – Bolivia;
  • M a berlepschi – N Chile, S Bolivia and NW Argentina;
  • M a armata – most of Chile (S from Atacama) and S Argentina (S from San Juan).

In a recent study using mtDNA and morphometric information, Gutiérrez-Pinto et al (2019) investigate this arrangement. Synonymizing belepschi, garleppi and turneri with leucogenis, the authors suggest that Torrent Duck may in fact compromise three monotypic species, denoted above with different text colour.


Figure 2 from Gutiérrez-Pinto et al (2019), showing sampling sites (a), differences in head pattern of drakes (b), and phylogeny (c).

The authors estimate the groups diverged c 567,000 years ago, with birds in the northern Andean lineage (mostly the known range of colombiana, although intriguingly also containing birds from northern Peru) are the most differentiated, having a smaller body size than central and southern birds, with less overlap in morphological measurements, and exhibiting the most genetic structure. While the central and southern lineages are seperable genetically, their morphologies are rather similar. The southern Andean lineage extends over the full range of armata, but also contains samples from as far as central Bolivia (previously referable to leucogenis); clearly the taxonomy and distributions of the relevant taxa remains rather vexed.

 

Reference

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. DOI: https://doi.org/10.1111/zsc.12367

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