Re: gardneri/study

["Bruce J. Turner" <fishgen at vt_edu>]

Indeed, you are correct. Many of the local populations that we know of in
gardneri, various chromoaphyosemion, the A. christyi complex, etc. are
chromosomally divergent and intersterile or nearly so in lab crosses.  This
seems to be primarily because the chromosomal differences are robertsonian
translocations which tend to lower fertility in F1 interpopulation hybrids
(heterozygotes for translocations, sometimes multiple translocations).
Sometimes these local populations are also divergent in color pattern, but
many times they are not, or at least the divergence among populations is no
greater than the variation within them. However, specialists in the African
rivulines (NOT including me) have traditionally been reluctant to recognize
forms taxonomically as distinct species if they are not also
morphologically divergent.(They will agree that the divergent forms are
really species, they just don't want to recognize them with different
names). Some colleagues insist that the divergence be in some aspect other
than color pattern---some measurable property (e.g., scale counts, fin rays
counts) that can be detected in museum specimens. This seems to be nowadays
a mostly European tradition.  It was Joegen Scheel's position, and it has
been adopted, sometimes explicitly, sometimes implicitly, by such modern
specialists as Huber, Radda and Wildekamp.  Thus we have the unsatisfactory
situation of a species name (e.g. gardneri) being used for more than one
biological species. Providing that people know what's going on, while I
don't particularly like this situation, I am not inherently bothered by it
too much.  The problem is that not everyone knows what's going on, and a
neophyte could be mislead into crossing populations with the same name,
only to generate sterile or nearly sterile hybrids.  This has actually
happened on more than one occassion...

******************************************************************************

					Bruce J. Turner
					Assoc. Professor of Biology
					VPISU, Blacksburg, VA 24061
					(540)-231-7444
					fishgen at vt_edu


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