Subject: [Tweeters] yellowlegs phylogeny
Date: Feb 24 17:53:52 2009
From: Dennis Paulson - dennispaulson at comcast.net
Hello, tweets.
I hoped I could steal away into the night without having to deal with
this confusing situation, but I'll try to write something about the
relationship of the tringine sandpipers, as Gene said I would. You
should delete if you're not into this stuff.
Here is the paper I'm discussing: Multiple gene evidence for parallel
evolution and retention of ancestral morphological states in the
shanks (Charadriiformes: Scolopacidae), by S?rgio Luiz Pereira and
Allan J. Baker, 2005. Condor 107 (3): 514-526.
I will try to do justice to the authors' conclusions, but I'll also
say why I'm not convinced about all of them.
They analyze mitochondrial DNA, nuclear DNA, and morphological
characters of the group we call the tribe Tringini. This includes
yellowlegs, greenshanks, redshanks, Marsh Sandpiper, Wood Sandpiper,
Green Sandpiper, Solitary Sandpiper, Willet, Spotted and Common
Sandpipers, Terek Sandpiper, and the two species of tattlers. The
very rare Nordmann's Greenshank wasn't analyzed, as they had no DNA
from it.
First of all, the Terek Sandpiper (Xenus cinereus) and Actitis
sandpipers (Common, A. hypoleucos, and Spotted, A. macularius) fall
out as separate from the other species and distinct from each other,
and I won't say anything more about them. The authors consider
everything else to be in the genus Tringa. All data show the Green
and Solitary Sandpipers to be closely related, and they are very
likely sister species, one for each hemisphere, with very similar
appearance and life style. The Wood Sandpiper is superficially
similar, but it doesn't group with them.
The mitochondrial DNA data put the Lesser Yellowlegs in a group with
Willet, Wood Sandpiper, Marsh Sandpiper, and Common Redshank, while
Greater Yellowlegs is grouped with Common Greenshank and Spotted
Redshank. Analysis of nuclear DNA doesn't resolve very much, although
it indicates Wandering and Gray-tailed Tattler being in different
clades, which isn't very believable, and Marsh Sandpiper separate
from the Lesser Yellowlegs group. But clearly this method won't
resolve the phylogeny of this group, so the authors must have
depended much more on mitochondrial DNA for their molecular
phylogenetic tree on p. 520, which basically grouped them as follows:
1) Green and Solitary a sister group to all other Tringa; 2) within
the remaining group, the two tattlers a sister group to all the
others; 3) within the remaining group, Greater Yellowlegs, Common
Greenshank, and Spotted Redshank a sister group to all the others,
and the yellowlegs and greenshank more closely related than either is
to the redshank; 4) within the remaining group, Lesser Yellowlegs and
Willet a sister group to another group containing Wood Sandpiper,
Common Redshank, and Marsh Sandpiper. Within the latter group, Wood
Sandpiper and Spotted Redshank more closely related than either is to
the Marsh.
They seemed to pay little attention to the morphological dataset,
which clearly separates the Willet from the classical long-legged
shanks. But morphology may not be too important to show relationships
in a group in which there is strong selection on all sorts of shape
variation for different foraging niches. DNA work on Dunlin, if I
recall correctly, shows that changes in morphology evolve quite
rapidly, differentiating populations that show little genetic
difference.
The paper states as one of its conclusions, "Our analysis indicated
that T. melanoleuca [Greater Yellowlegs] is more closely related to
the Greenshank (T. nebularia), as previously suggested by Mayr and
Short (1970) and T. flavipes [Lesser Yellowlegs] is more closely
related to Catoptrophorus [Willet]. Indeed, body structure, color of
bare parts, and call notes are more similar between these two species
than between the two yellowlegs (Hayman et al. 1986)."
I guess the authors are talking about Greater Yellowlegs and Common
Greenshank here. I agree that these two are quite similar, but notice
they didn't have anything to say about the purported relationship
between Lesser Yellowlegs and WIllet, the latter dramatically
different from both yellowlegs. They never did address why they were
willing to accept a close relationship between these two species.
The authors also state, about the yellowlegs, "They can be
distinguished by call notes, shape of bill, and body size but these
species may overlap in size, which confounds species identification
(Hayman et al. 1986)." I hadn't realized Hayman et al. had said the
two yellowlegs overlap in size, but that is quite false, and their
acceptance of that makes me wonder how well the authors know these
birds.
It has been stated that perhaps the Greater Yellowlegs is a mimic of
the Lesser, thus their extreme similarity. I'd probably call it
convergence rather than mimicry, and the same situation with the
extremely similar (differing in size, bill size, and call note, just
like the yellowlegs) Common Greenshank and Marsh Sandpiper. All four
species are what I call "sentinel" shorebirds, which I wrote about in
Birding a few years ago. Other shorebirds such as Stilt Sandpiper and
Wilson's Phalarope might mimic the similar-sized Lesser Yellowlegs to
associate with it for protection from predators, but I'm not all
convinced that it would be good evolutionary strategy for the larger
species (GRYE) to mimic the smaller (LEYE).
The fine details of plumage are pretty much identical within the
species pairs of the two yellowlegs and the greenshank/Marsh
Sandpiper, but the two Eurasian species are very different from the
yellowlegs, and this more than anything causes me to question the
phylogenetic conclusions in this paper. I see no reason in any
mimicry/convergence scenario for the minute details of plumage to
become that similar. The plumage of Stilt Sandpipers and Wilson's
Phalaropes have not become similar to that of the yellowlegs, if
indeed they are mimicking the flight patterns of the Lesser
Yellowlegs. Nor have Red Knots become similar in plumage to Black-
bellied Plovers, if they are mimicking their flight pattern. I think
if there truly is mimicry, as I speculated in the Birding article, it
is only in flight pattern, not in all aspects of plumage.
The authors separate the two species of redshanks phylogenetically
and write as if that is surprising. But I have never considered
Spotted Redshank and Common Redshank closely related just because
they both have red legs. There are many more differences between them
than there are between the yellowlegs or between greenshank and Marsh
Sandpiper. The winter ranges of the two redshanks don't overlap as
much as the yellowlegs winter ranges, so I'm even more skeptical of
mimicry/convergence in this pair.
Finally, how do you get a Willet from a Lesser Yellowlegs? That's a
lot harder than solving a problem like Maria. Moving from foraging in
the water to foraging on mudflats could lead to the evolution of
shorter legs. Perhaps there is more competition from smaller
shorebirds on the mudflats, which could lead to the evolution of
larger size. I can't explain why the flashy wing pattern of a Willet
would evolve from the plain pattern of a yellowlegs, nor why all of
their vocalizations would be so different. Note that the two
dowitcher species have quite different flight calls, but their songs
are almost identical, and the two yellowlegs have much more similar
songs than either does to a Willet. Even if the flight calls of the
yellowlegs converged to facilitate their association in winter
flocks, there is no reason for their songs to have converged. I'm
still not convinced of the validity of all parts of this phylogeny.
NOTE: I am in no way belittling the use of molecular tools to study
relationships of organisms. I think we are very fortunate that we
have these tools available, and they have given us tremendous
insight. They probably don't answer all the questions.
So take a closer look at those yellowlegs and their relatives next
time you encounter them.
Dennis
-----
Dennis Paulson
1724 NE 98 St.
Seattle, WA 98115
206-528-1382
dennispaulson at comcast.net
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman1.u.washington.edu/pipermail/tweeters/attachments/20090224/5e5d1b26/attachment.htm