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From: snell@utzoo.UUCP (Richard Snell)
Newsgroups: sci.bio
Subject: Animal hybridization: gulls 
Message-ID: <7817@utzoo.UUCP>
Date: Mon, 23-Mar-87 09:19:02 EST
Article-I.D.: utzoo.7817
Posted: Mon Mar 23 09:19:02 1987
Date-Received: Mon, 23-Mar-87 09:19:02 EST
Organization: U of Toronto Zoology
Lines: 57

Keywords: evolution speciation clines

In article <14184@cca.CCA.COM> g-rh@cca.UUCP writes
>	You are talking about clines (a chain of sub species).  a specific
>example is the herring gull cline consisting of
>
>(1) The British lesser black-backed gull, Larus fuscus graellsii,
>(2) Scandanavian lesser black=backed gull, Larus fuscus fuscu,
>(3) Siberian vega gull, Larus argentatus vegae,
>(4) American herring gull, Larus argentatus smithsonianus,
>(5) British herring gull, Larus argentatus argentatus
>
>1 can interbreed with 2, 2 with 3, and so on, but 5 and 1 cannot
>interbreed.  The difference is one of size -- the British herring
>gull is twice as big as the lesser black-backed gull.
         ^^^^^^^^^^^^


What are your sources for the statements that 2 can breed with 3,
and 3 with 4.  What evidence do you have that 4 ever _actually_ breeds 
with 5?  A few references would be nice.

In fact, 1 and 5 certainly _can_ interbreed, as was shown by
the experimental inducement of hybrization by 
M.P. Harris (Ibis 112:488, 1970).
Harris includes a partial review of the instances of non-experimentally
induced (i.e., natural) hybridization between these two types of gull.

As well, the difference between these "species" is _not_ size.  
It is primarily colour, particularly the colour of the back.  
Here are some data on the `size' of 
the males of these birds (data from _Birds of the Western Palearctic,
 Vol. 3_, by Cramp and Simmons, 1983).

                        Herring Gull    Lesser Black-backed Gull
                        (L. argentatus) (L. fuscus)

average winglength      425 mm          430 mm
average tail length     170 mm          163 mm
range of weights        750-1150 g      770-1000 g


The systematics of these large gulls is most complex.  It is also
poorly understood.  The supposed subspecies mentioned above may, or
may not, represent biologically meaningful units.  Of course, the issue
of whether _any_ subspecies are taxonomically meaningful is quite separate
from any discussion of clines and their significance.

A brief summary of the current taxonomy of these two "species"
Herring Gulls (Larus argentatus) and Lesser Black-backed Gulls (Larus fuscus)
is in Cramp and Simmons.

__
Name:   Richard Snell
Mail:   Dept. Zoology, Univ. Toronto
        Toronto, Ontario, Canada    M5S 1A1
UUCP:   {allegra,decvax,ihnp4,linus,pyramid,yetti}!utzoo!snell