Invertebrate Zoology Laboratory Assignment #2 (100 pts)
Due on 10/07/13 on Turnitin.com and as a hardcopy in lab
Background. Phylum Cnidaria contains two major body forms: the polyp and the
medusa. The polyp stage is mostly sessile, while the medusa stage is adapted for dispersal
and a planktonic lifestyle. While polyps may be benthic and mostly sessile, they have a
remarkable ability to clone themselves, and these clones can take over a landscape (rock)
and even float away on debris, thereby dispersing the population. Alternatively, medusae
live in the plankton (i.e., the open water column), which requires the ability to regulate
buoyancy (float), swim (although this is limited by water movement), and feed on other
swimming animals. However, not all medusae are big predators, as you’ll see in the
publication on the moon jellyfish. Below are a series of questions taken from both your
laboratory observations and the two publications listed below that test your knowledge
about the ecology and biology of a local anemone (Diadumene lineata) and scyphozoan
(Aurelia aurita). Both species are common to our coastline – the anemone is an invasive
species found on boat docks, and the jellyfish is regularly found washed up on our shores
during the summer and fall seasons.
Publications.
Costello, JH & Colin, SP. 1994. Morphology, fluid motion and predation by the
scyphomedusa Aurelia aurita. Marine Biology 121: 327-334.
Ting, JH & Geller, JB. 2000. Clonal diversity in introduced populations of an Asian sea
anemone in North America. Biological Invasions 2: 23-32.
Directions. Answer all questions presented below. Unless the question asks you to list
your answers, please use complete sentences. Poor grammar and sentence structure will
affect your grade. Do not copy your answers directly from the publications – this is
plagiarism and you will receive no credit. Do not use quotes; instead, use your own
words when answering each question with a complete sentence. Upload this file to
Turnitin.com prior to coming to lab and also turn in a hardcopy (paper) to the TA James
Gallant in lab on the day it is due. Late hardcopies or electronic copies will receive an
automatic 10% deduction from the final grade (or other penalties according to the TA).
________________________________________________________________________
1. In the Ting and Geller (2000) publication, what two lines of evidence suggest that
introduced populations of the sea anemone, Diadumene lineata, are mononclonal? Based
on this evidence, the authors derived two hypotheses. What is the primary experimental
hypothesis that Ting and Geller (2000) are testing in their study, and what is their null
hypothesis? (8 pts total = 2 pts per answer)
2. Where were the two native populations of anemones sampled? (1 pts each = 2 pts)
3. The authors isolated DNA from their clonal anemones of different populations around
North America using an SSCP assay and amplified the ITS region (internal transcribed
spacer sequence) between ribosomal genes of individual anemones. The ITS region is
known to be sensitive enough to detect different genotypes within a species. However,
the authors acknowledge that they migh have underestimated genotypic diversity? Why?
(10 pts)
4. The authors found that genotypic diversity was high (i.e., aneomes were ployclonal) in
populations of Diadumene lineata despite what previous authors have hypothesized.
What three characteristics were reported in previous investigations to hypothesize
(incorrectly) that anemones were strictly monoclonal. (10 pts total)
5. Briefly explain the advantages of clonal growth in D. lineata in terms of local
extinction versus region extinction. Why is this important for an invader such as D.
lineata? (20 pts)
6. Aurelia aurita does not generally feed on large invertebrates, which would be difficult
with such tiny oral tentacles. Instead, most prey are quite small and are often caught on
the exumbrellar surface of Aurelia. How do these potential prey items get to the mouth if
they are caught on the opposite side of the body? (10 pts).
7. Medusae like species of Aurelia aurita swim by pulsing their bell, which occurs in two
alternating phases of circular muscle contraction and relaxation. Briefly describe this
process, indicating what happens to the bell diameter, bell cavity (=subumbrellar space),
and movement of the medusa as it pulses along. (10 pts)
8. If, during swimming, the same water that was pushed out of the bell cavity was then
sucked back in on the subsequent pulse, the medusa would only move and back forth in
the same spot, and hence never eat. Briefly explain how swimming movements of the
medusa function to draw prey items toward the animal. Be sure to explain how prey are
then caught, disabled, and brought to the mouth. (20 pts)
9. Aurelia aurita is often considered to be a generalist feeder. However, prey selection is
expected to change as a medusa grows from ephyra to adult. Provide an explanation for
this change in prey selection based on biomechanics. (10 pts)