From: simon@dcs.warwick.ac.uk (Simon Clippingdale)
Subject: Response to Ken Mann (Was: Why Fossils Cannot be Used as Evidence)
Organization: Department of Computer Science, Warwick University, England
Date: Sun, 27 Sep 1992 21:11:31 GMT

In article <19920922.121630.653@almaden.ibm.com> mannk@fshvmfk1.VNET.IBM.COM (Ken Mann) writes:
> Simon Clippingdale writes:
>> One animal CAN evolve into another because they have been OBSERVED DOING
>> JUST THAT.

> Can you please site some of these OBSERVATIONS?

Sure thang, with apologies for the ages of the sources I looked up (not
being a biologist, I went to reference works rather than the original
refereed literature, but you can doubtless find the originals fairly
easily).

You may wish to bear in mind White's comment below that most of the
difference between sibling species arises after speciation (after
reproductive isolation is established), and that at the epoch of
speciation, little difference may be discernible although, in the
terms of the question, one animal has technically evolved into another
at that point.

No doubt new examples of speciation have been observed since these;
quoting Chris Colby's Evidence For Evolution FAQ:

# Speciation has been observed 4 times in the last 110 years in the
# wild. It has been forced in the lab a few times (see the August 1992
# issue of Evolution for a new example involving polychaete worms --
# I'll try to summarize this on t.o. if I have time.)

Some of the _Drosophila_ stuff I'm about to quote was thought to arise from
interaction between D. and microorganisms; more light may be shed by the
following reference, again from Chris's FAQ, which apparently deals with 
wasps:

# Breeuwer and Werren, 1990, Microorganisms associated with chromosome
# destruction and reproductive isolation between two insect species,
# Nature 346: 558 - 560

What follows are my extracts from Futuyma, _Evolutionary Biology_, 2nd
edition, 1986, Sinauer (tagged F:) and White, _Modes of Speciation_, Freeman,
1978 (tagged W:). Speciation by polyploidy, although far more prevalent
in plants, is noted by White (quote below) as a mode of speciation in
some animals (see also recent discussion here on _Tragopogon_ and ref.
(again courtesy Chris Colby) Roose and Gottlieb, 1976, Genetic and
Biochemical Consequences of Polyploidy in _Tragopogon_, Evolution 30:
818 - 830).

Drosophila stuff first:

F: Finally, laboratory experiments have often shown that incipient reproductive
F: isolation can develop between isolated populations of _Drosophila_ and
F: houseflies (_Musca domestica_) that are exposed to divergent artificial
F: selection for responses to light, gravity, or chemical features of the
F: food medium (e.g., del Solar 1966, Soans et al. 1974, de Oliveira and
F: Cordeiro 1980). -- Futuyma p226

F: In one case, finally, a new biological species has arisen spontaneously in
F: a laboratory. A strain of _Drosophila_paulistorum_ when first collected was
F: interfertile with other strains but developed hybrid sterility after being
F: isolated in a separate culture for just a few years (Dobzhansky and
F: Pavlovsky 1971). -- Futuyma p246

W: The remaining taxa of the [_Drosophila_] _paulistorum_ complex ... are
W: genetically isolated from one another by a combination of premating,
W: ethological factors and the usually complete sterility of the hybrid
W: males. [...] A strain from Llanos, Colombia, which produced fertile
W: male hybrids when crossed with Orinocan forms in 1958, no longer did
W: so from 1963 onward (Dobzhansky and Pavlovsky, 1967, 1971). Some wild
W: strains intermediate between Orinocan and Interior, and which originally
W: produced fertile male hybrids with both, lost the ability to produce
W: fertile male hybrids with the Interior semispecies after about a year
W: in the laboratory (Dobzhansky and Pavlovsky, 1975). -- White pp 68-69

More on this in White, pp 39-42.


On polyploidy:

F: Most models of sympatric speciation are highly controversial; the only
F: exception is one mode of instantaneous speciation, speciation by polyploidy,
F: that occurs in plants. [...] Such polyploid complexes have been described
F: for many plant genera (Grant 1981). -- Futuyma p228

W: Evolutionary polyploidy is much more widespread in the plant kingdom
W: than among animals ... Evolutionary polyploidy in animals is largely
W: confined to hermaphroditic and parthenogenetic forms, although a few
W: genuine cases are now known in some bisexual groups, particularly the
W: anuran amphibians. -- White p261


And two interesting general comments; first on the fact that most differences
arise subsequent to, rather than being the cause of, the speciation event:

W: Most of the genetic divergence between so-called closely related species
W: (even sibling species) is due to phyletic evolution which has occurred
W: subsequent to evolutionary separation, and has little or nothing to do
W: with speciation as such. -- White p43

and a nice one for doubters in principle of speciation:

W: There can be absolutely no doubt about the reality of allopatric
W: speciation; if populations are geographically isolated for a long
W: enough period of time they _will_ evolve into different species.
W: This is the one type of speciation whose actual existence is
W: uncontroversial. Controversy has developed, however, as to whether
W: all (or almost all) speciation conforms to the allopatric model
W: (or models, since there are a number of variants on the basic theme).
W: -- White p107

> Shalom!  |  INTERNET: mannk@fshvmfk1.vnet.ibm.com
>   Ken    |  VNET:     FSHVMFK1(MANNK)
>          |  IBMnet:   mannk@saskatchewan.fishkill.ibm.com
>-----------------------------------------------------------
>               You can only coast downhill!

Cheers

Simon
-- 
Simon Clippingdale                simon@dcs.warwick.ac.uk
Department of Computer Science    Tel (+44) 203 523296
University of Warwick             FAX (+44) 203 525714
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