From: max@hilbert.cyprs.rain.com (Max Webb)
Subject: Re: Oahu wallabies (was Re: Logic and God)
Organization: Cypress Semiconductor Northwest, Beaverton Oregon
Date: Thu, 3 Sep 1992 23:34:06 GMT

In article <715512375.16997@minster.york.ac.uk> cjhs@minster.york.ac.uk writes:
>Seconded. Peter Lamb in particular went to a lot of trouble to check
>out the Oahu wallaby story, and I also looked up what references I
>could. As far as I am aware, the assertion frequently made in this
>group that the Oahu wallabies are incapable of interbreeding with their 
>Australian cousins is entirely supposition, and I would have thought it
>is a pretty unlikely supposition. (Disclaimer -- my opinion is that of
>a complete novice at biology; more informed guesses welcome.)

I don't think it is unlikely, although not proven, that there is some
degree of reproductive isolation.  Here is a brief summary of one of
the references often cited here in this group; it describes a mechanism
that appears to enhance rapid speciation. Here is my summary of it's contents.

::::include previous article::::
In the Australian Journal of Zoology, 1990, 37, pages 351-363 is an
article entitled "Chromosome Evolution, Phylogeny, and Speciation
of Rock Wallabies (Petrogale:Macropodidae)".

Those who claim that species walls are fixed, inviolate boundaries
should take a look at this. They collected wallabies at 200km intervals
throughout their known range. There are (according to this author)
21 different taxa, grouped in 11 species. The taxa come with varying
degrees of reproductive isolation - hybrids are not wholly infertile.
[So much for inviolable species boundaries ]. Question for the
creationists: Did Noah visit australia, traversing it's surface, and
depositing wallabies with subtly different chromosomal structure, to
create a distribution of species and semi-species? Or are you willing
to grant us that speciation occurs?

...

The concept here is stasipatric speciation. A "migrating male, derived
from a colony newly homozygous for the structural rearrangement,
could invade a nearby small, local colony of rock wallabies, and be
established as the alpha male of that colony. Here the structural
change would rapidly become established because of homozygote superiority".

Heterozygosity more adversely effects the fertility of males than females.
His less fertile heterozygous sons would be dominated by him, and over 
the next 6  to 12 years he would mate several more times with his
(somewhat fertile) heterozygous daughters. Either the colony will flip
to become  homozygous in the new gene struture, or the new gene structure
will die out. "An analogous situation was found at the godmani-Mareeba
race hybrid zone where allelic gene frequencies suggested capture
of a godmani colony by a single migrating male of the Mareeba race".

Returning to the Oahu wallabies: if the escaping pair of wallabies were
heterozygous in chromosomal character (likely given the great
variety of taxa), this combination of social structure, and hybrid
subfertility would force the outcropping to become homozygous for
some combination of the characters of the original pair. Once this
occurs, the Oahu wallabies would be maximally fertile within their clan,
and subfertile without.It doesn't take too long for this process to
produce good species with 100% reproductive isolation. In fact, _two_
iterations seem to be able to do it, by my reading of the article.

Based on this article, I would be surprised to find that some reproductive
isolation had not occurred. But it still doesn't substantiate the claim
that the Oahu wallabies form a 'good' species.

Regards
	Max G. Webb
::::end quotation::::