Usenet post by Joseph E Boxhorn. Forwarded to ANNELIDA for comment. I have not
yet seen the paper referred to. (For non-usenetters an FAQ is a document of
Frequently Asked Questions (with answers :-)) GBR.
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From: jboxhorn at alpha1.csd.uwm.edu (Joseph E Boxhorn)
Newsgroups: talk.origins
Subject: Observed Speciation FAQ
Date: 20 Mar 1996 03:56:56 GMT
Organization: Information & Media Technologies, University of Wisconsin -
Milwaukee
Lines: 79
Distribution: world
Some recently published data calls into question whether one of the
examples listed in the Observed Instances of Speciation FAQ actually
represents a speciation event. In the FAQ I wrote:
> 5.7 Speciation in a Lab Rat Worm, Nereis acuminata
> In 1964 five or six individuals of the polychaete worm, Nereis
> acuminata, were collected in Long Beach Harbor, California. These were
> allowed to grow into a population of thousands of individuals. Four
> pairs from this population were transferred to the Woods Hole Oceanographic
> Institute. For over 20 years these worms were used as test organisms in
> environmental toxicology. From 1986 to 1991 the Long Beach area was
> searched for populations of the worm. Two populations, P1 and P2, were
> found. Weinberg, et al. (1992) performed tests on these two populations
> and the Woods Hole population (WH) for both postmating and premating
> isolation. To test for postmating isolation, they looked at whether
> broods from crosses were successfully reared. The results below give
> the percentage of successful rearings for each group of crosses.
> WH X WH 75% P1 X P2 77%
> P1 X P1 95% WH X P1 0%
> P2 X P2 80% WH X P2 0%
> They also found statistically significant premating isolation between
> the WH population and the field populations. Finally, the Woods Hole
> population showed slightly different karyotypes from the field
> populations.
Please note that the conclusions drawn above depend upon an assumption
that either P1 or P2 represent an ancestral strain to the Woods
Hole strain. Given this we would expect to find a goodly amount of
genetic similarity between at least one of the wild strains and the
lab strain. This should be especially true for allozyme loci. This
is because these enzymes are held to be fairly neutral to selection.
In a follow up to this study, Rodriguez-Trelles, et al. (1996) used
allozyme electrophoresis to examine 18 genetic loci in 12 enzyme
systems in several Nereis populations including the original study
populations. They then compared the Woods Hole population to both
of the Long Beach populations and a population from the Atlantic
Ocean.
The Woods Hole strain showed no variability at any of the 18 loci.
At 13 of the loci it had no alleles in common with either the P1 or
P2 population. At 2 more loci alleles were fixed in the Woods Hole
strain that were present at low frequencies in the P1 and P2 strains.
The authors estimated that the probability of getting the alleles
they found in the Woods Hole strain by random choice from either
P1 or P2 was 5.3 X 10^(-6).
The Nei's genetic distances between the Woods Hole strain and P1
and P2 are respectively 1.75 (+/- 0.51) and 1.76 (+/- 0.52).
These distances are larger than what is seen between most pairs
of congeneric species in many sorts of organisms. They are on the
order or the genetic distances found between the P1 (and P2) strain
and the Atlantic Ocean strain (1.36 +/- 0.40).
The authors conclude that the Woods Hole strain probably
represented, at collection in 1964, a different species from P1
or P2. I feel that in view of the fact that one of the authors of
the original paper is also an author of this new paper, we should no
longer consider this an example of observed speciation.
Rodriguez-Trelles, F., J. R. Weinberg and F. J. Ayala. 1996.
Presumptive rapid speciation after a founder event in a
laboratory population of Nereis: Allozyme electrophoretic
evidence does not support the hypothesis. Evolution.
50:457-461.
Weinberg, J. R., V. R. Starczak and P. Jora. 1992. Evidence for rapid
speciation following a founder event in the laboratory.
Evolution. 46:1214-1220.
--
Joseph Boxhorn (jboxhorn at csd.uwm.edu)
Department of Biological Sciences University of Wisconsin--Milwaukee
"Coffee does not make you nervous - your own inadequacies do this.
Coffee merely increases your perception of your own shortcomings."
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Geoff Read <gread at actrix.gen.nz>
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