Chlorella NOT speciation. ?Contamination.

James Mahaffy (mahaffy@dordt.edu)
Fri, 29 Nov 1996 11:14:24 -0600 (CST)

Folks,

Glen in a recent post (Mon, 25 Nov 1996 19:27:26) cited "the change in
family in a microscopic single celled creature which was observed to
suddenly become a multicellular life form." In the post he refers to
Talk Origins post of an alga, Chlorella pyrenoidosa (vulgaris) that
changed its form to "being in the genus Coelosphaerium, which is in a
different family from Chlorella" (Quote from Boxhorn). Sorry folks not
everything, even on the venerable Talk Origins is good science, and this
WOULD NOT be a good example to cite for speciation. It is not Glenn's
fault (he can hardly be expected to know algae genera). In fact I don't
even recall the genus, Coelosphaerium, and I TAed phycology once at the
U. of Illinois. But I do know how easy it is to contaminate cultures
and that I lot of the colonial (better term than multicellular) forms
can have unicellular stages.

But when I looked up the genus Coelosphaerium in my phycology (algae)
text, I found that it was not only a different family - it was a blue
green. This would have implied a kingdom switch from a eukaryot (having
a nucleus) to a prokaryot. While more devolution, that would be an
earth shaking change, which if provable could be published in Science
and not posted to folks that don't know algae (most protozoa folks don't
either - so maybe the researchers thought it just changed its form). It
was most likely a case of contamination. I raise some algae for class
and it is not that easy to get unialgal cultures and keep them that way.
I have had several of
mine get contaminated by blue greens. Might also mention that many of
the marine algae have a life cycle which has two radically different
forms. In one form they can be a filamentous structure and in another
part of their life cycle a different enough form that sometimes the same
alga was originally classified as two different genera. A good example
of this is some of the large Kelps, big brown algae, that have a
gametophyte stage (1N) that is filamentous and microscopic.

-- 
:
James F. Mahaffy                   e-mail: mahaffy@dordt.edu
Biology Department                 phone: 712 722-6279
Dordt College                      FAX 712 722-1198
Sioux Center, Iowa 51250