Last week, someone asked for a summary of Zink's paper in which he
advocates splitting the Fox Sparrow (_Passerella iliaca_) into 4
species. Here goes:

Zink, R.M. 1994. The geography of mitochondrial DNA variation, population
structure, hybridization, and species limits in the Fox Sparrow
(_Passerella iliaca_). Evolution 48: 96-111.

Zink looked at geographic variation of mitochondrial DNA haplotypes at 39
localities throughout the range of the species. He found 4 lineages that
corresponded to 4 morphological/geographical groups of subspecies: the
"_iliaca_" or Red group (n. Alaska to Newfoundland), "_unalaschcensis_" or
Sooty (Aleutian Islands to Vancouver Is.), "_megarhynchus_" or
Thick-billed (California), and "_schistacea_" or Slate-colored (Rocky
Mountains and Great Basin). _unalaschcensis_ and _schistacea_ were the
two most closely related taxa, and _iliaca_ was the most divergent.
There was little mtDNA variation within each of the 4 lineages.

Under the phylogenetic species concept, these would be 4 species.
He says: "Phylogenetic species are minimally diagnosable clusters of
individuals, which may or may not be reproductively isolated (Cracraft
1983, 1987, 1989; de Queiroz and Donoghue 1988).", p. 106.
However, since there
is limited hybridization among the four groups, especially between the
Slate-colored and Thick-billed groups, advocates of the biological species
concept would argue for fewer species. Exactly how many is difficult to
guess. Zink says: "In short, biological species are taxa that are
reproductively isolated; degree of isolation required for species status
varies among authors (Mayr 1963, 1982).", p. 106. Zink says that,
depending on how much hybridization advocates of the biol. sp. concept
might come up with 1, 3, or 4 species. He goes on to say: "Such
decisions depend upon arbitrary decisions about the frequency of
hybridization required to confer species status.", p. 106. He also
says: "Hybridization is an ancestral condition, of no value in grouping
taxa into the species category (Rosen 1979, Cracraft 1983, McKitrick and
Zink 1988). Hybridization between _megarhyncha_ and _schistacea_involves
apparently non-sister taxa (species). A 'species'
consisting of _megarhyncha_ plus _schistacea_ is paraphyletic (Fig. 3)
and would be of no use in any comparative exercise (Brooks and McLennan
1991). Treating _megarhyncha_ and _schistacea_ as conspecific, but
_iliaca_ and _unalaschcensis_ as separate species would misrepresent the
recovered pattern of evolutionary history (Fig. 3)." I should also add
to Zink's statements by pointing out that
there is often reproductive compatibility between
genera, but not between species within those genera. This also suggests
that reproductive isolation may occur after speciation, rather than as a
necessary precursor to it.

So take your pick: 4 phylogenetic species, or 1-4 biological species
(depending on how you feel). For the listers, wait for the next
supplement to the AOU checklist.

I didn't want to paraphrase Zink, since he said everything s
succinctly. In the paper, he also discusses the apparent lack of
similarity of the Fox
Sparrows' mtDNA geographic variation with that of other organisms. He
does admit, however, that such variation has been studied in few
other taxa.

Anthony Lang, Dept. of Zoology | "Always keep your
Univ. Toronto, Ontario, Canada, M5S 1A1 | stick on the ice."
tony at zoo.toronto.edu | RED GREEN

==========================

From: "Byron K. Butler" <BBUTLER at yalevm.ycc.yale.edu>
Subject: Mayr; also the PSC

From: Byron K. Butler, Guilford, CT

By now, everyone on BirdChat is aware of Zink's Fox Sparrow(s) paper
in t the Feb, 1994 issue of Evolution. However, no one has mentioned that
the first 43 pages consist of tributes to Ernst Mayr by several different
authors. One of these is by Frank Gill and is titled, "Ernst Mayr, the
ornithologist." On page 17 Gill discusses the phylogenetic species concept
(PSC), comparing it to the biological species concept (BSC). This is
especially relevant to Zink's paper. The entire first 43 pages of this
issue make for very interesting and enlightening reading for all
interested in 20th century evolutionary thought.

Gill's paper in this issue also cites Walter Bock.1994. Ernst Mayr,
naturalist: his contributions to systematics and evolution. Biology and
Philosophy 9:1-61.