SUBJECT: Osmoconformers
DATE: 10/95; 5/96
We have a lab on osmoregulators and osmoconformers that we like a great
deal.
Students collect data over a two day period and they must graph it to draw
conclusions. It is a good lab that makes them think; they can't know the
results
intuitively.
We have been using shore crabs (Hemigrapsus) and peanut worms (Sipunula).
We
want to use an animal, not a protist or plant. One of the goals in Organismal
Biology, a majors course, is to provide an opportunity to see a wide variety
of
organisms.
We are having trouble getting the worms. Does anyone know a good "osmoconformer?
Thanks.
Christine Case
Skyline College
case@smcccd.cc.ca.us
At the BIOLAB workshop several summers ago we used mussels as examples of
osmoconformers. Mussels are generally available in grocery stores these
days. We used small pieces of glass rod to hold the shells open and
observed substantial weight loss or gain within an hour. It is pretty
neat to see that "control" animals, without the peg to keep the
shell
open, are able to exclude the external water and show no weight change.
I have used Paramecium and have had several groups of students do a very
good job of correlating contractile vacuole rate with salinity. However,
I agree completely with Janice that this is not for freshmen. The
majority of students experienced only frustration -- only those with
previous microscopy experience and/or a high level of dedication were
successful, and this success required about six weeks of work. If I were
to try this sort of lab again, I would work with the mussels.
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Robert B. Ketcham Biology (302) 831-2377
Laboratory Coordinator Univ of Delaware rketcham@strauss.udel.edu
Newark, DE 19716-2590
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We have used Pugettia sp. kelp crabs as our osmoconformer for a number of
years, with considerable success. They make a useful comparison of diversity
of water balance control in related organisms. The main disadvantage may
be
that they are moderately expensive.
Rob Longair
Dept. of Biological Sciences
University of Calgary
Calgary, Alberta
CANADA T2N 1N4
Phone (403) 220-7387
Fax (403) 289-9311
longair@acs.ucalgary.ca
We use earthworms in our Zoology lab for an experiment on osmoconformers.
Bill
Rogers (RogersW@Winthrop.edu) developed the lab and has a write-up available.
He simply places the earthworms in test tubes for a period of time and reweighs
them.
From: greggk@acad.winthrop.edu
We also have used earthworms in general zoology labs in an experiment that
Sam McGinnis and I devised over the years. Currently the worms are
subjected to various conditions that simulate their natural environment,
i.e., wet and dry "pavement", wind conditions, puddles of water,
misty
rain, and control soil habitats. We decided this was more realistic after
a number of years of subjecting worms to changes in salinities and
measuring responses by changes in body weight.
I would be glad to send along information on the lab, but folks will have
to wait until mid-December when I get back to Hayward from a sabbatical
leave at Harvard [elyke@oeb.harvard.edu].
Appreciate the suggestions for other animals to use in these types of
experiments.
Regards, Ned Lyke
From: elyke@s1.csuhayward.edu (Edward Lyke)
5/96
We do an osmoregulator/osmoconformer lab at Swarthmore in Biology 2 and
it
works splendidly. We use fiddler crabs (Uca pugilator) for the
osmoregulators and bloodworms (Glycera dibrachiata) for the osmoregulators.
Both live in intertidal environments where salinities fluctuate, but the
worms normally live in burrows where they can escape much of the salinity
fluctuation. This gives you a chance to talk about physiological vs.
behavioral osmoreguation, and to point out that the experiment doesn't
necessarily give the animals a chance to do what they would in nature.
We submerge the animals (groups of 5 fiddler crabs or 3 worms) in the
following concentrations of seawater: 8, 24 and 40 ppt. The bloodworms
tend to bloat and become lighter colored in the 8 ppt solution, and to
become darker in the 40 ppt solution. The nice thing about Glycera is that
you can see the blood cells bumping around in the segmental gills with just
a dissecting microscope, much like the little balls in very old-fashioned
gas pumps (am I showing my age?). Students really get a kick out of seeing
this, because they imagine that they can't see cells at this level of
magnification.
We submerge the animals in the solutions for a total of 100 minutes, and
the students weigh the animals every 20 minutes so they can watch the time
course of the effect. We use pieces of fine netting (the kind you can get
in the fabric store) as weighing containers for the worms; the worms should
be handled carefully with the net, not with hands or forceps, as much as
possible. For the crabs, we use a tupperware container with holes punched
in the bottom as a weighing container. Students need to develop a method
for blotting the weighing containers consistently for each weighing. Keep
the worms at 24 ppt when not being used in the experiment.
You may find the following papers on related species useful in interpreting
results. We put them on reserve so students can read them when they write
their lab reports:
Norfolk, J.R.W. 1978. Internal volume and pressure regulation in Carcinus
maenus. J. exp. Biol. 74:123-132.
Shumway, S.E. and J. Davenport. 1977. Some aspects of the physiology of
Arenicola marina (Polychaeta) exposed to fluctuating salinities.
57:907-924.
We get the bloodworms from Maine Bait Company, Academy Street, Box 204,
New
Castle, ME 04553. Phone 207-563-3000.
The fiddler crabs come from Gulf Specimen, P.O. Box 237, Panacea, FL
32346. Phone 904-984-5297. Uca pugilator are better than the U. pugnax,
which is what we would get if we went to collect them ourselves. U.
pugilator keep much more easily in the lab and are more likely to feed from
the sand. We have been able to keep them for weeks and have students from
several different classes (biomechanics, physiology, etc.) use them for
projects after we're done with them in Bio 2.
Let me know if you need more info.
Sara Hiebert
Biology Department
Swarthmore College
Swarthmore, PA 19081
610-328-8053
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