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Jeffrey Lotz jlotz at medea.gp.usm.edu
Wed Apr 5 08:05:54 EST 1995

derek a. zelmer (zelmeda4 at WFU.EDU) wrote:
: On 4 Apr 1995 CGE at CU.NIH.GOV wrote:

: > Personally, I've always viewed commensalism as a benign form of
: > parasitism in any case. This is in part because the same species can
: > be a 'commensal' in one host and a 'parasite' in a different host
: > (Zelmer definitions). An infection may also start out as 'commensal'
: > but due to environmental or other factors become 'parasitic'. Is it
: > worth having two rigid terms to describe what may be transient
: > conditions?

: As I alluded to earlier, I don't believe in commensals. They could only occur
: in the strictest sense, if an infection provided the host with some benefit
: that exactly counteracted the negative of the infection. The condition,
: therefore would not be transient. A parasite, no matter how benign, is 
: not a commensal.

: > Perhaps the definition of a parasite
: > should be: a eukaryote living in or on another eukaryote on which it
: > is dependent and from which it derives nutritional benefits. Unless
: > you WANT to include bacteria and viruses of course.

: I'd even include prions...but then again, I'm not fussy. The only reason 
: I could use to justify seperating the prokaryotes is their replication in 
: definitive hosts, but this is characteristic of some eukaryotes as well.

: > My list of commensals/parasites would probably be very
: > similar to Derek's ecto-/endo-symbionts.

: y list of symbionts includes parasites, but is a much longer list.

: 			Derek Zelmer

I would include viruses, bacteria etc. as parasites. I wouldn't agree that
a commensal is only when the cost/benfits are zero. There is probably an
interval from -x to +y where it doesn't matter. That is natural
selection can't tell the difference among - 0 +. So commensalism is
probably not a single point on the cost/benefit axis with no length but is an

Jeffrey M. Lotz                     Phone (601) 872-4247
Gulf Coast Research Lab             Fax   (601) 872-4204
P.O. Box 7000                       Internet: jLotz at medea.gp.usm.edu
Ocean Springs, MS 39566-7000 USA

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