Anas is a genus of dabbling ducks. It includes mallards, wigeons, teals, pintails and shovelers in a number of subgenera. Some authorities prefer to elevate the subgenera to genus rank. Indeed, as the moa-nalos are very close to this clade and may have evolved later than some of these lineages, it is rather the absence of a thorough review than lack of necessity that this genus is rather over-lumped.
of this genus is one of the most confounded ones of all living birds. Research is hampered by the fact the radiation of the two major groups of Anas
- the teals
and mallard groups -; took place in a very short time and fairly recently, roughly in the mid-late Pleistocene
. Furthermore, hybridization
probably has long played a major role
evolution, with within-subgenus hybrids regularly and between-subgenus hybrids not infrequently being fully fertile. The relationships between species are much obscured by this fact, and mtDNA sequence
data is of dubious value in resolving their relationships; on the other hand, nuclear DNA
sequences evolve too slowly to resolve the phylogeny
of the subgenus Anas
Some major clades can be discerned. For example, that the traditional subgenus Anas, the mallard group, forms a monophyletic (in the loose sense, i.e. non-holophyletic) group has never been seriously questioned by modern science and is as good as confirmed (but see below). On the other hand, the phylogeny of the teals is very confusing.
It is fairly clear by now that the dabbling duck lineages more distantly related to mallard group (which includes the type species of Anas) than the wigeons are should arguably be separated in their own genera. These would include the Baikal Teal, the Garganey, the spotted black-capped Punanetta group, and the shovelers and other blue-winged species. Whether the widgeons, which are very distinct in morphology and behavior, but much less so in mtDNA cytochrome b and NADH dehydrogenase subunit 2 sequences, should also be considered a distinct genus Mareca (including the Gadwall and Falcated Duck) is essentially the one remaining point of dispute as regards the question which taxa should remain in this genus and which ones should not.
The following arrangement is based on morphological, molecular and behavioral characters and presents apparent major evolutionary groupings compared to the subgenera the species were placed in at one time or another.
Probable genus Sibirionetta - Baikal Teal
Probable genus Querquedula - Garganey (may include Punanetta)
Probable genus Punanetta
Probable genus Spatula - blue-winged ducks/shovelers and allies (polyphyletic?)
Possible genus Mareca - wigeons (may include Chaulelasmus and Eunetta)
Subgenus Chaulelasmus - Gadwall
Subgenus Eunetta - Falcated Duck
Subgenus Dafila - pintails
Subgenus Nettion - teals (paraphyletic)
- Indian Ocean clade
- Atlantic/Red-and-green head clade
- New Zealand clade (Placement unresolved)
Subgenus Melananas - African Black Duck
Subgenus Anas - mallard and relatives (may include Melananas)
- Basal African species ("Afranas")
- American clade
- Mottled Duck, Anas fulvigula - sometimes included in Anas platyrhynchos
- Florida Duck, Anas fulvigula fulvigula - sometimes included in Anas platyrhynchos
- American Black Duck, Anas rubripes - sometimes included in Anas platyrhynchos
- Mexican Duck, Anas diazi - sometimes included in Anas platyrhynchos
- Pacific clade - the moa-nalos might be derived from this group.
- Mallard, Anas platyrhynchos
- Spotbill, Anas poecilorhyncha
- Chinese Spotbill, Anas (poecilorhyncha) zonorhyncha - sometimes considered a subspecies of Anas superciliosa
Formerly placed in Anas:
A number of fossil
species of Anas
have been described. Their relationships are often undetermined:
- Anas sp. (Late Miocene of China)
- Anas sp. (Late Miocene of Rudabánya, Hungary)
- Anas greeni (Ash Hollow Late Miocene?/Early Pliocene of South Dakota, USA) - Nettion red-and-green head clade (doubtful)?
- Anas ogallalae (Ogalalla Late Miocene?/Early Pliocene of Kansas, USA) - Nettion red-and-green head clade (doubtful)?
- Anas pullulans (Juntura Late Miocene?/Early Pliocene of Juntura, Malheur County, Oregon, USA) - Punanetta?
- Anas cheuen (Early-Middle Pleistocene of Argentina) - Dafila?
- Anas bunkeri (Early -? Middle Pliocene - Early Pleistocene of WC USA) - Nettion red-and-green head clade?
- Bermuda Islands Flightless Duck Anas pachyscelus (Shore Hills Late Pleistocene of Bermuda, W Atlantic)
- Anas schneideri (Late Pleistocene of Little Box Elder Cave, USA)
Several prehistoric waterfowl supposedly part of the Anas assemblage are nowadays not placed in this genus anymore, at least not with certainty:
- "Anas" basaltica (Late Oligocene of "Warnsdorf", Czechia) is apparently an indeterminate heron.
- "Anas" blanchardi, "A." consobrina, "A." natator are now in Mionetta
- "Anas" creccoides (Early-mid Oligocene of Belgium), "A." risgoviensis (Late Miocene of Bavaria, Germany) and "A." skalicensis (Early Miocene of "Skalitz", Czechia), though possibly anseriform, cannot be placed with any certainty among modern birds at all.
- "Anas" albae (Late Miocene of Polgárdi, Hungary), "A." eppelsheimensis (Early Pliocene of Eppelsheim, Germany), "A." isarensis (Late Miocene of Aumeister, Germany) and "A." luederitzensis (Kalahari Early Miocene of Lüderitzbucht, Namibia) are apparently Anatidae of unclear affiliations; the first might be a seaduck.
- "Anas" integra and "A." oligocaena are now in Dendrochen
- "Anas" robusta is now tentatively placed in Anserobranta
- "Anas" velox (Middle - Late? Miocene of C Europe) and "A." meyerii (Middle Miocene of Öhningen, Germany; possibly the same species) do not seem to belong into the present genus either; they may still turn out to be ancestral dabbling ducks.
Highly problematic, albeit in a theoretical sense, is the placement of the moa-nalos. These are in all probability derived from a common ancestor of the Pacific Black Duck, the Laysan Duck, and the Mallard, and an unknown amount of other lineages. Phylogenetically, they may even form a clade within the traditional genus Anas. However, as opposed to these species - which are well representative of dabbling ducks in general - the moa-nalos are the most radical departure from the anseriform bauplan known to science. This illustrates that in a truly evolutionary sense, a strictly phylogenetic taxonomy may be difficult to apply.
- Bernor, R.L.; Kordos, L. & Rook, L. (eds): Recent Advances on Multidisciplinary Research at Rudabánya, Late Miocene (MN9), Hungary: A compendium. Paleontographica Italiana 89: 3-36. PDF fulltext
- Carboneras, Carles (1992): Family Anatidae (Ducks, Geese and Swans). In: del Hoyo, Josep; Elliott, Andrew & Sargatal, Jordi (editors): Handbook of Birds of the World, Volume 1: Ostrich to Ducks: 536-629. Lynx Edicions, Barcelona. ISBN 84-87334-10-5
- Johnson, Kevin P. & Sorenson, Michael D. (1999): Phylogeny and biogeography of dabbling ducks (genus Anas): a comparison of molecular and morphological evidence. Auk 116(3): 792–805. PDF fulltext
- Johnson, Kevin P. McKinney, Frank; Wilson, Robert & Sorenson, Michael D. (2000): The evolution of postcopulatory displays in dabbling ducks (Anatini): a phylogenetic perspective. Animal Behaviour 59(5): 953–963 PDF fulltext
- Kulikova, Irina V.; Drovetski, S. V.; Gibson, D. D.; Harrigan, R. J.; Rohwer, S.; Sorenson, Michael D.; Winker, K.; Zhuravlev, Yury N. & McCracken, Kevin G. (2005): Phylogeography of the Mallard (Anas platyrhynchos): Hybridization, dispersal, and lineage sorting contribute to complex geographic structure. Auk 122(3): 949-965. [English with Russian abstract] DOI: 10.1642/0004-8038(2005)122[0949:POTMAP]2.0.CO;2 PDF fulltext Erratum: Auk 122(4): 1309. DOI: 10.1642/0004-8038(2005)122[0949:POTMAP]2.0.CO;2
- Livezey, B. C. (1991): A phylogenetic analysis and classification of recent dabbling ducks (Tribe Anatini) based on comparative morphology. Auk 108(3): 471–507. PDF fulltext
- McCracken, Kevin G.; Johnson, William P. & Sheldon, Frederick H. (2001): Molecular population genetics, phylogeography, and conservation biology of the mottled duck (Anas fulvigula). Conservation Genetics 2(2): 87–102. PDF fulltext
- Sorenson et al (1999): Relationships of the extinct moa-nalos, flightless Hawaiian waterfowl, based on ancient DNA. Proceedings of the Royal Society.