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From: dplatt@teknowledge-vaxc.UUCP
Newsgroups: talk.origins,sci.bio
Subject: Re: question about animal hybridization
Message-ID: <10980@teknowledge-vaxc.ARPA>
Date: Fri, 20-Mar-87 14:30:04 EST
Article-I.D.: teknowle.10980
Posted: Fri Mar 20 14:30:04 1987
Date-Received: Sun, 22-Mar-87 21:30:07 EST
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In-reply-to: lew@ihlpa.ATT.COM's message of 20 Mar 87 15:48:29 GMT
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Lew Mammel, Jr. asks,

> My question is, is there an example of this intransitivity among
> known populations of animals? ( N.B. animals, not plants! )

I'm not sure about the biological angle (intergroup fertility), but
I'm pretty sure that there is at least one known case involving the
standard definition of species (intergroup interbreeding).  There is a
"ring" of species of arctic birds (gulls, I believe) that exhibits
this sort of behavior.  As I recall, the species are believed to have
diverged from one parent stock, by progressive migration in an
eastwards direction over a fairly long period of time.  Adjacent
groups can (and do?) interbreed, with one exception.  If you go to the
point at which the circle "wraps around" to the point at which it
started, you'll find that the species that "wrapped around" has
diverged sufficiently from the original variety (which still populates
that area) that the two do not (cannot?) interbreed viably.

Sorry I don't remember the details on this... I'll see if I can dig
them up sometime soon.