Hi tweets,

There's an interesting article in the latest Auk on systematics of the
dabbling ducks, by Kevin P. Johnson and Michael D. Sorenson. They analyzed
cytochrome-b and ND2 mitochondrial gene DNA sequences in these species, and
compared them to the morphological phylogeny developed by Bradley Livezey,
published in 1991, which served as the basis of the AOU check-list
committees's recent reshuffling of these taxa. This study illustrates both
the rapid progress that is being made in sorting out the evolutionary
relationships and biogeograhy of species using new techniques, and also how
far we still have to go in understanding these relationships. Every new
discovery conflicts to some extent with earlier evidence while in other
ways reinforcing it, and so -- as someone said here recently -- science,
like life, is dynamic and evolutionary.

Hare are some of the discoveries announced in this article. Expect these
to be reflected in various ways in field guides and check-lists four to ten
years out.

-- there is extremely low genetic divergence between Blue-winged Teal and
Cinnamon Teal, which means that either these two taxa diverged very
recently, or hybridization and introgression has occurred recently. It is
a case of two taxa appearing to the human mind, with its preconceptions and
the primacy it gives to visual evidence, as more different than they
"really" are.

-- there is extremely high divergence between the Green-winged Teal of
North America and the Common Teal of Eurasia, which are very similar in
appearance and have been treated as two forms of a single species by most
recent authorities (including the AOU). This genetic divergence is as
great as that between (for example) Mallard and Northern Pintail. Further,
the authors found that the sister taxon of the "Green-winged" form (Anas
carolinensis) is not the "Common" form (A. crecca), but the Speckled Teal
of South America (A. flavirostris), suggesting that flavirostris evolved
from birds colonizing South America from the Northern Hemisphere.

-- there are two genetically distinct forms of the Mallard, and both exist
in North America. One is closely related to Asian/Pacific taxa such as
Spot-billed Duck, while the other is closely related to North American taxa
such as Mottled Duck and American Black Duck. A great deal more study is
needed to sort out the distribution of these two types around the planet,
and the phylogenetic and biogeographical implications thereof.

-- the pintail and mallard groups have an African origin, as may the teal
group as well.

-- all the dabbling ducks have Southern Hemisphere origins. There have
been at least eight independent colonization events of the Northern
Hemisphere, and at least one recolonization of the Southern Hemisphere from
the Northern Hemisphere, but perhaps as many as five.

Here is a greatly simplified summary of the phylogeny of the four subgroups
of dabbling ducks, based on this study. Only the species that occur in
North America are listed. The first three subgroups constitute the genus
Anas; the fourth subgroup, consisting of four other genera, is South
American.

I. Wigeons-teals-pintails-mallards.
A. Pintails
1. A. acuta (Northern Pintail)
2. A. bahamensis (White-cheeked Pintail)
B. Teals
1. A. carolinensis (Green-winged Teal)
2. A. crecca (Common Teal)
C. Mallards
1. A. platyrhynchos (Mallard)
2. A. poecilorhyncha (Spot-billed Duck)
3. A. rubripes (American Black Duck)
4. A. fulvigula (Mottled Duck)
D. Wigeons
1. A. americana (American Wigeon)
2. A. penelope (Eurasian Wigeon)
3. A. strepera (Gadwall)
4. A. falcata (Falcated Duck)
II. Blue-winged ducks.
A. A. querquedula (Garganey)
B. A. clypeata (Northern Shoveler)
C. A. cyanoptera (Cinnamon Teal)
D. A. discors (Blue-winged Teal)
III. A. formosa (Baikal Teal)
IV. South American genera
A. Amazonetta
B. Tachyeres
C. Lophonetta
D. Speculanas

This issue of Auk contains two studies of this same sort on the phylogeny
of the blackbirds (Icteridae), which I have yet to read in detail, and
scads of other fascinating articles.

Hal Opperman
Medina, Washington
halop at accessone.com
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: text/enriched
Size: 4808 bytes
Desc: not available
Url : http://mailman1.u.washington.edu/pipermail/tweeters/attachments/19990813/f5314831/attachment.bin