Anas
Female Mallard (Anas platyrhynchos) with brood of young, a typical member of this genus. Female Mallard (Anas platyrhynchos) with brood of young, a typical member of this genus.
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Aves Order: Anseriformes Family: Anatidae Genus: Anas Linnaeus, 1758
Species
Some 40-50; see text.

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 (Carboneras 1992). 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.

Systematics

The phylogeny 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 in Anas evolution, with within-subgenus hybrids regularly and between-subgenus hybrids not infrequently being fully fertile (Carboneras 1992; see also Mariana Mallard). The relationships between species are much obscured by this fact, and mtDNA sequence data is of dubious value in resolving their relationships (e.g. Kulikova et al. 2005); on the other hand, nuclear DNA sequences evolve too slowly to resolve the phylogeny of the subgenus Anas for example.

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 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 (Livezey 1991) and behavior (Johnson et al. 2000), but much less so in mtDNA cytochrome b and NADH dehydrogenase subunit 2 sequences (Johnson & Sorenson 1999), should also be considered a distinct genus (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 (Livezey 1991), molecular (Johnson & Sorenson 1999, McCracken et al. 2001) and behavioral (Johnson et al. 2000) characters and presents apparent major evolutionary groupings compared to the subgenera the species were placed in at one time or another.



Probable genus N.N.

• Baikal Teal, Anas formosa (formerly in Nettion)

Probable genus Querquedula - Garganey (may include Punanetta)

• Garganey, Anas querquedula

Probable genus Punanetta

• Silver Teal, Anas versicolor
• Puna Teal, Anas puna - formerly included in Anas versicolor
• Hottentot Teal, Anas hottentota

Probable genus Spatula - blue-winged ducks/shovelers and allies (polyphyletic?)

• Blue-winged Teal, Anas discors
• Cinnamon Teal, Anas cyanoptera
• Borrero's Cinnamon Teal, Anas cyanoptera borreroi - possibly extinct (late 20th century?)
• Red Shoveler, Anas platalea
• Cape Shoveler, Anas smithii
• Australasian Shoveler, Anas rhynchotis
• Northern Shoveler, Anas clypeata

Possible genus Mareca - wigeons (may include Chaulelasmus and Eunetta)

• Eurasian Wigeon, Anas penelope
• Amsterdam Island Duck, Anas marecula - tentatively placed here; extinct (c.1800)
• American Wigeon, Anas americana
• Chiloe Wigeon, Anas sibilatrix

Subgenus Chaulelasmus - Gadwall

• Gadwall, Anas strepera
• Washington Island Gadwall, Anas strepera couesi - extinct (c.1880s)

Subgenus Eunetta - Falcated Duck

• Falcated Duck, Anas falcata

Subgenus Dafila - pintails

• Northern Pintail, Anas acuta
• Eaton's Pintail, Anas eatoni
• Kerguelen Islands Pintail, Anas eatoni eatoni
• Crozet Islands Pintail, Anas eatoni drygalskii
• Yellow-billed Pintail, Anas georgica
• South Georgia Pintail, Anas georgica georgica
  

  Male Northern Pintail, Anas acuta
• Niceforo's Pintail, Anas georgica niceforoi - extinct (1950s)
• White-cheeked Pintail, Anas bahamensis (formerly Poecilonetta)
• Red-billed Teal, Anas erythrorhyncha (formerly Poecilonetta)
• Cape Teal, Anas capensis (formerly in Nettion)

Subgenus Nettion - teals (paraphyletic)

• Indian Ocean clade
• Bernier's Teal, Anas bernieri
• Mauritian Duck, Anas theodori - extinct (late 1690s)
• Sunda Teal, Anas gibberifrons
• Rennell Island Teal, Anas gibberifrons remissa - extinct (c.1959)
• Grey Teal, Anas gracilis - formerly included in Anas gibberifrons
• Chestnut Teal, Anas castanea

• Green-winged/Red-and-green head clade
• Common Teal, Anas crecca
• Green-winged Teal, Anas carolinensis - formerly included in Anas crecca
• Speckled Teal, Anas flavirostris
• Andean Teal, Anas (flavirostris) andinum
• New Zealand clade (Placement unresolved)
• Auckland Islands Teal, Anas aucklandica
• Brown Teal, Anas chlorotis - formerly included in Anas aucklandica
• Macquarie Islands Teal, Anas cf. chlorotis - prehistoric
• Campbell Island Teal, Anas nesiotis - formerly included in Anas aucklandica

Subgenus Melananas - African Black Duck

• African Black Duck, Anas sparsa

Subgenus Anas - mallard and relatives (may include Melananas)

• Basal African species ("Afranas")
• Meller's Duck, Anas melleri
• Yellow-billed Duck, Anas undulata

• 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.
• Mariana Mallard, Anas (platyrhynchos) oustaleti - sometimes considered a subspecies of Anas superciliosa; extinct (1981)
• Hawaiian Duck, Anas wyvilliana - sometimes included in Anas platyrhynchos
• Philippine Duck, Anas luzonica
• Laysan Duck, Anas laysanensis - sometimes included in Anas platyrhynchos
• Lisianski Duck, Anas cf. laysanensis - hypothetical; extinct (c.1845)
• Pacific Black Duck, Anas superciliosa
• Ambiguous
• Mallard, Anas platyrhynchos
• Spotbill, Anas poecilorhyncha
• Chinese Spotbill, Anas (poecilorhyncha) zonorhyncha - sometimes considered a subspecies of Anas superciliosa

Formerly placed in Anas:

• Bronze-winged Duck, Speculanas specularis
• Crested Duck, Lophonetta specularioides
• Salvadori's Teal, Salvadorina waigiuensis

A number of fossil species of Anas have been described. Their relationships are often undetermined:

• Anas velox (Middle - Late? Miocene of C Europe) - Nettion red-and-green head clade?
• Anas isarensis (Late Miocene of Aumeister, Germany)
• Anas sp. (Late Miocene of Rudabánya, Hungary: Bernor et al. 2002) - mid-sized species
• 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, USA) - Punanetta?
• Anas eppelsheimensis (Early Pliocene of Eppelsheim, Germany) - Nettion red-and-green head clade?
• Anas cheuen (Early-Middle Pleistocene of Argentina) - Dafila?
• Anas bunkeri (Early -? Middle Pliocene - Early Pleistocene of WC USA) - Nettion red-and-green head clade?
• Anas pachyscelus (Shore Hills Late Pleistocene of Bermuda, W Atlantic)
• Anas schneideri (Late Pleistocene of Little Box Elder Cave, USA)

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 form a clade with the traditional genus Anas (Sorenson 1999). 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 not always be desirable.

References

• 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. doi:10.1023/A:1011858312115 PDF fulltext
• Sorenson et al (1999): Relationships of the extinct moa-nalos, flightless Hawaiian waterfowl, based on ancient DNA. Proceedings of the Royal Society.