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RE: A. striatum identification/sibling species
Thanks for the clarification.
mike
-----Original Message-----
From: Bruce J. Turner [mailto:fishgen at vt_edu]
Sent: Thursday, May 09, 2002 2:52 PM
To: killietalk at aka_org
Subject: RE: A. striatum identification/sibling species
Dear Mike: yes, "sibling species" and "cryptic species" usually refer to
the same thing. For reasons that I do not understand completely, "sibling
species" seems to have won out as a term for general use. I would have
preferred "cyrptic," for "sibling" is too readily confused with "sister
species" for my taste, and the two concepts are different. The best
definition of sibling species that I know of for the lay reader is in Ernst
Mayr's new book, "What Evolution Is, " in box 8.1 on pg 167. I wouldn't
change Mayr's definition at all, except that there are many allopatric
sibling species as well as sympatric ones. It has been clear for quite
some time that many of our "species" of West African rivulins are likely
arrays opf morphologically nearly identical sibling species which are often
more chromosomally divergent than their similar morphologies would suggest.
This much was already clear from Scheel's work. The problem is, no one is
following up with more detailed work...
There is a little experiment that folks can do to convince themselves of
the existence of these sibling species:
1. Cross F. gardneri Misaje with F. gardneri Akure in either reciprocal
combination. These two populations nominally belong to the same
subspecies, I think F. g. "nigerianum." Riase the hybrid progeny but do
not sell or distribute them in any way. You will find that you get
fast-growing, vigorous F1 hybrids that are very pleasing to look at as well.
2. Try to interbreed the hybrids. You will have males and females, and
they will happily spawn the whole day long. But very little or nothing
will ever hatch. Backcrossing to the female Akure parent (if you have made
your cross in that direction) will hield a few progeny. Backcrossing to
the female Misaje parent will yield almost nothing again...
3. Destroy/discard the hybrids.
>Dr. Turner,
>You wrote, "...in fact, we use a special name, "sibling species' (different
>from "sister species") when "good" species cannot readily be distinguished
>morphologically."
>
>Is this the same thing as "cryptic species"? Is "cryptic species" a term
>that is properly applied to killifish?
>
>Thanks,
>mike
>
>-----Original Message-----
>From: Bruce J. Turner [mailto:fishgen at vt_edu]
>Sent: Thursday, May 09, 2002 1:00 PM
>To: killietalk at aka_org
>Subject: Re: A. striatum identification.
>
>
>Please let me add my plea to Wright's. If you didn't get it with a
>locality designation, then don't use one, no matter how well you think you
>may have "back idnetified" your stock, and even if this means your material
>goes without a locality designation altogether. We already have enough
>sources of potential confusion without adding to the mix.
>
>In saying the above, I am also struck by the irony of how the "worm has
>turned" over the years. When locality designations were first introduced
>by Scheel and others who knew that many populations of bitaeniatum,
>bivittatum, gardneri, etc. were chromosomally divergent and would likely
>yield sterile hybrids if crossed, people often did not want to use them.
>Dealers, in particular, would complain bitterly about the absence of common
>names, and getting them to use a locality designation was all but
>impossible, possibly because the practice was unfamiliar. Long time
>breeders were almost equally reluctant. And then there were the arm chair
>biologists who learned about "binomial nomenclature" in school and for some
>reason thought that the use of a locality designation. impeached the purity
>of the nomenclature... Nowadays locality designations are so widely used
>that their absence seem to make people feel insecure... I suspect that the
>use of locality designations by collectors and importers of Rift Lake
>cichlids during the same period may have helped these gain acceptance among
>killifish specialists too. Certainly, they helped with dealers---ours here
>in the Blacksburg area are comfortable with "gardneri Akure," "gardneri
>Misaje," etc.
>
>One other note and at the risk of lecturing (which is what I do for a
>living and into which mode I drop too readily): Chomosomally divergent and
>intersterile populations of Aphyosmemion, Chromaphyosemion, Fundulopanchax,
>etc. are likely validly considered distinct species (under the biological
>species concept). Scheel was aware of this, and of the fact that many
>biologsts would have given each chromosomally distinct form a different
>name (i.e., described them as new species). He was reluctant to do this
>because he wanted his species to be morphologically divergent as well, even
>though that is NOT part of the biological species concept---in fact, we use
>a special name, "sibling species' (different from "sister species") when
>"good" species cannot readily be distinguished morphologically. Scheel's
>views are evidently held also by his colleagues/successors like Wildekamp,
>Huber,and Radda. When I was younger (and a bit more inclined to be
>arrogant or dogmatic) I argued about this with Joergen at some length --
>for I felt that his attitude was quite "retro" (or even reactionary). And,
>as Joergen would be the first to admit, it does make the locality
>designations (which are sometimes labels for distinct sibling species) very
>important, and these are obviously easily lost or confused in the course of
>subsequent exchanges, commerce, etc. For those who like history, it might
>be fun to know that the arguments between Joergen and myself exactly
>parallel a famous series of disagreements in evolutionary genetics between
>A.H. Sturtevant and T. Dobzhanksy when sibling species of Drosophila, which
>differed only in their chromosomes, were discovered in the
>1930's---Sturtevant didn't want to name them because he feared that would
>make life too difficult for the "museum man" (as he put it) who needed to
>have species based on morphology; Dobzhansky disagreed, and ultimately
>prevailed, which is why we have species today like D. simulans, D.
>persimilis, D. similis, etc.
>
> However, recently I have begun to realize that Scheel's practice is a
>good interim measure. It enables us to keep stocks derived from different
>populations separate and labelled a long time before we have had a chance
>to assess the level of their actual chromosomal or genetic distinctiveness.
>This fauna, by modern standards, is only superficially surveyed, and it
>merits detailed work, and by this I mean effort beyond the "alpha" level---
>population-by-population chromosomal, morphological, and general genetic
>surveys. These are not, to my knowledge, now being done. In the future,
>when someone emerges who devotes his/her career to doing this, some of our
>different stocks will doubtless prove to be conspecific in the rigorous
>sense, while other will likely need to be labeled as distinct species.
>
>***************************************************************************
*
>**
>
> Bruce J. Turner
> Assoc. Professor of Biology
> VPISU, Blacksburg, VA 24061
> (540)-231-7444
> fishgen at vt_edu
>
>
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****************************************************************************
**
Bruce J. Turner
Assoc. Professor of Biology
VPISU, Blacksburg, VA 24061
(540)-231-7444
fishgen at vt_edu
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Join the AKA at http://www.aka.org/AKA/Applic.htm
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