Proposal
Marine Ecology
March 17, 2009
64/80
No species or site info
No stats
No interpretation
No accept/reject
Membranipora membranacea Defense Signal Propagation
By: Jamie Gordon, Kelly O’Loughlin, and Amanda Worsham
Question
How do predator-induced defense signals propagate through Membranipora membranacea colonies when exposed to Doridella steinbergae predation?
Introduction 4/4
The propagation and transmission of signals within colonial species are not well understood. One species that sends signals as a result of colony connectivity is the bryozoan, Membranipora membranacea. Bryozoans are an abundant colonial intertidal species, which play an important role in the intertidal by sustaining diversity through competition with other sessile creatures and providing food for various invertebrates (Gordon 1972), making it an excellent candidate for the study of colonial signal transmission. However, these bryozoans negatively affect seagrass communities by reducing the ability of kelp to absorb nitrates from seawater (Hurd and Durante et al. 1994) reducing the kelps’ growth and reproduction (Hepburn et al. 2006). It has been shown that the nudibranch Doridella steinbergae, the bryozoan’s primary predator, induces a predatory response causing the heterozooids in the colony to develop defensive spines around its perimeter. Since Membranipora membranacea is an invasive species in some areas, it would be advantageous to know how the colony communicates a predatory response to help preserve the health and diversity of the intertidal through environmentally friendly regulations of the bryozoans. Once we know the mechanism of transmission we can relate colonal connectivity of bryozoans to other colonial organisms such as corals, hydrozoan jellies, pyrosomes, and salps. This information could then be used for conservation and protection of colonial organisms. It has been discovered that the signal is transmitted through the finuncular network (Ruppert et al. 2004), while the propagation of predator induced defense signals through Membranipora membranacea colonies when exposed to Doridella steinbergae is unknown. We would like to know if these signals are circumvented around the colony or from the point of predation out in a radial manner. Work on colony connectivity can prove very useful for future projects involving colonial organisms.
Pattern 2/2
When part of the bryozoancolony, Membranipora membranacea, is attacked or eaten, the zooids on the perimeter of the colony grow spines to help ward off further predatory attacks. The spines do not grow in the center or middle of the attacked colony. Once a colony has been attacked it retains the spines it has developed but does not grow any additional spines in the absence of future attacks. (For graphs see Figures 1 and 2). 4/4
Goals 2/2
We would like to analyze colony connectivity in the colonial bryozoan, Membranipora membranacea, in order to determine the pathway of signal propagation resulting from predation by the nudibranch, Doridella steinbergae.
Hypotheses 6/6
HG1: The defense signal is only transmitted around the perimeter zooids in the colony after an attack by Doridella steinbergae on Membranipora membranacea, inducing the growth of spines.
HS1: If the zooids are removed from the perimeter at two opposing locations on the colony of Membranipora membranacea, disconnecting the perimeter zooids and a predator is introduced to one half of the colony, then the zooids on the attacked half will grow spines and the zooids across the colony from the predator will not grow spines. (Figure 3).
HS2: If the colony of Membranipora membranacea is cut in half, and a predator attacks one half, the zooids on the opposing half will not grow any spines and the perimeter zooids on the attacked half will grow spines. (Figure 4).
HG2: The defense signal is transmitted throughout the entire colony after an attack by Doridella steinbergae onMembranipora membranacea, inducing the growth of spines.
HS3: If the zooids in the center of the Membranipora membranacea colony are removed and a predator is introduced on the outer perimeter, signals will propagate through all zooids in the Membranipora membranacea colony, resulting in the growth of spines on all inner and outer perimeter zooids. (Figure 5).
HS4: If the zooids in the center of the Membranipora membranacea colony are removed and a predator is introduced on the inner perimeter, signals will propagate through all zooids in the Membranipora membranacea colony, resulting in the growth of spines on all inner and outer perimeter zooids. (Figure 6).
Methods 4/5 per (no stats)
For all experiments, we will harvest bryozoans colonies from kelp holdfasts found on the beach or in tide-pools. For our first experiment, that supports our first specific hypothesis, we will remove the perimeter zooids from two opposite edges of the colony by pulling out the soft body part of the bryozoans with tweezers under a dissecting microscope (Figure 3). There will be two tanks, a treatment tank and a control tank. In each of these two, ten gallon tanks, we will place five bryozoans colonies. The water temperature and tank atmosphere will be kept at natural intertidal conditions. We will place one nudibranch on each of the five colonies for the treated tank and no nudibranches will be placed in the control tank.
For our second experiment, that supports our second specific hypothesis, we will remove the central transect of zooids from each colony (Figure 4). This will leave the colony completely cut in half, but still close together. We will remove the zooids by, again, pulling out the soft body part of the bryozoans with tweezers under a dissecting microscope. In each of two, ten gallon tanks, we will place five of the separated bryozoans colonies. There will be one treatment tank and one control tank. The water temperature and tank atmosphere will be kept at natural intertidal conditions. A nudibranch will be placed on one half of each of the five colonies in the treatment tank, and no nudibranches will be placed in the control tank.
For our third experiment, that supports our third specific hypothesis, we will remove the central zooids from the colony creating a “doughnut hole” in the middle (Figure 5). We will remove the soft body parts of the bryozoans again by using tweezers under a dissecting microscope. In each of two, ten gallon tanks, we will place five colonies with their middle sections removed. The water temperature and tank atmosphere will be kept at natural intertidal conditions. A nudibranch will be placed on the outer edge of the five colonies in the treatment tank, and no nudibranches will be placed in the control tank.
For our fourth experiment, that supports our fourth specific hypothesis, we will remove the central zooids exactly as we did in experiment three (Figure 6). There will be two, ten gallon tanks. One tank will be a treatment tank and one will be a control. The water temperature and tank atmosphere will be kept at natural intertidal conditions. A nudibranch will be placed on each of the five colonies in the treatment tank, however instead of introducing them to the outer edge, they will be introduced to the inner perimeter of the colony where the zooids were removed.