Help with taxonomy of protists
Charles F Austerberry
cfauster at BLUEJAY.CREIGHTON.EDU
Thu Aug 25 09:47:42 EST 1994
I teach a course I call "Biology of the Protists" here at
Creighton University. I come to the protists as a molecular/cellular
biologist, having done work on genome rearrangement in Tetrahymena. Of
course, my relative ignorance of most other protists is rather humbling,
especially in the areas of systematics and ecology. Nonetheless, the
students and I have a lot of fun doing the best we can. Jim Berger
helped me out a lot by sending me a text he and F.J.R. Taylor developed
for their course at Univ. of British Columbia, which I used to
strenghten my own background. As for my course, I use Michael Sleigh's
text "Protozoa and other Protists," (I hope it continues to be updated,
or at least stays in print, because I know of no good alternatives). I
also use Jahn, Bovee, and Jahn's key to the protozoa.
I think this discussion group will prove very valuable to me. Can anyone
offer answers to one or more of the following questions? Thanks!
1. Earlier this summer Andrew Roger, David Patterson, and Mark Siddall
debated the meaning of monophyly, and the value of the term holophyly.
That got me thinking about phenetics and cladistics approaches to
classifying protists. I'd like to provide the students with protistan
examples of how different approaches to systematics results in different
classification schemes. In particular, I'd like to use a) some examples in
which the difference rests on whether or not one attempts to distinguish
between common ancestry and convergence for some trait or traits, and
b) some examples in which the difference rests on whether or not one
attempts to distinguish between derived and primitive ancestral traits. Any
2. One set of traits of obvious importance would be plastid presence,
type, etc. That chloroplasts have been lost often seems clear. The
origin of chloroplasts is not so clear. The current trend in the literature
seems to favor a
monophyletic origin of plastids from some cyanobacterial ancestor, with
secondary symbioses within eukaryotes (e.g., cryptomonads). Wolfe et al.
(Nature Vol. 367, p. 566, Feb. 10 1994) have evidence of
light-harvesing-complex proteins in red algal chloroplasts
(Porphyridium), and Larkeum et al. (PNAS Vol. 91, 679-683, Jan. 1994)
have evidence of chlorophyll c-like pigment (along with chlorophylls a and
b) in Prochloron. So, is it reasonable to speculate that the photosynthetic
prokaryote that became the first chloroplast could have had phycobilisomes,
antenna complex proteins, and all three chlorophylls? Or, is it more
likely that the use of certain chlorophylls evolved multiple
times independently? Finally, how about the idea of a polyphyletic
origin for chloroplasts, a la Dodge? Is that still viable?
3. F.J.R. Taylor and others have placed great emphasis on the morphology of
mitochondrial cristae, but somewhere I read that mitochondrial cristae might
assume a variety of shapes depending upon the physiological state of the
cell at the time of fixation, as well as the method of fixation. What
seems to be the current majority opinion on the value of mitochondrial
cristae as a characteristic for systematics?
4. Tom Fenchel and Catherine Bernard discovered a ciliate with purple
endosymbionts, and suggested that this supported Woese' idea that
mitochondria evolved from photosynthetic nonsulphur bacteria rather than
from heterotrophic bacteria. Any comments? (Fenchel and Bernard, Nature
Vol. 362, p. 300, 25 March 1993).
Thanks again for any help you can give me. I hate feeling "out of the
loop," but I haven't been able to attend many meetings.
Dept. of Biology
Omaha, NE 68178-0103
cfauster at creighton.edu
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