Bursatella leachii - behaviour

March 11, 2001
From: James

Like in earlier messages I too am faced with the AP biology assignment about Bursatella leachii. I'm sure you remember it you had so many requests for help.

The question:
A scientist working with Bursatella leachii, a sea slug that lives in an intertidal habitat in the coastal waters of Puerto Rico, gathered the following information about the distribution of the sea slugs within a ten-meter square plot over a 10-day period. Distribution of slugs within a ten-meter square plot. Midnight 8 cm between individuals; 4a.m. 8.9; 8a.m. 44.8; noon 174; 4p.m. 350.5; 8p.m. 60.5; midnight 8.

Then you have to using the data provided
• (1)summarize the pattern.
• (2)Identify three physiological or environmental variables that would cause the slugs to vary their distance from each other.
• (3)and explain how each variable could bring about the observed pattern of distribution.
• Finally choose one of the variables that you identified and design a controlled experiment to test your hypothetical explanation. Describe results that would support or refute your hypothesis.

I have read all of the other student's requests and your responses. I did discover a web site that might help http://www.neurobio.upr.clu.edu/neuroethology-98/field.htm.
It is titled: FIELD STUDIES IN PUERTO RICO and describes a study on the behaviour Bursatella. In brief it suggests that they separate during the day to feed and then regroup at night to reproduce.

Should you find more information regarding this please share it with me. If it is true that they separate during the day to feed and then regroup at night to reproduce then observing them in an aquarium setting over a peroid of time would clearly prove or disprove this idea.
What do you think?
My best to you,
James

james_elk@msn.com

James, 2001 (Mar 11) Bursatella leachii - behaviour. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/3919

Dear James,
Firstly thanks very much for finding this site - the project described there certainly seems to be the source of the question. In my earlier replies I had assumed that the 10 meter quadrat they described was representative of the whole population but that clearly can't be so. The quadrat must be an unrepresentative place where Bursatella retires at night. Obviously the quadrat they describe can't be surrounded by similar quadrats or there would be a traffic jam of Bursatella as they moved out of their quadrats to feed.

I have copied the relevant paragraph from the website you have discovered. The site is part of the University of Puerto Rico website and describes the Institute of Neurobiology's "Tropical Neuroethology program:"

Field Studies in Puerto Rico
The discipline of Ethology emphasizes the study of animal behavior in the field. Before the neural basis of any behavior (i.e. Neuroethology) can be studied, these behaviors must be characterized and quantified in the natural habitat of the animal. Field studies help to generate hypotheses, quantify natural behavior patterns, and verify their relevance to the animal. Some of the primary marine model systems used in neuroethological research are easily accessible in the coastal habitats of Puerto Rico. The species we are studying Bursatella leachi, the ragged sea hare, exhibits a variety of easily distinguishable behavior patterns and undergoes frequent transitions between these patterns. Some of the behavior patterns characterized in Bursatella are respiratory pumping, head waving, feeding, grazing, and copulating. Field observations are made using snorkeling and diving techniques, including underwater photography. Observations are usually made early in the morning when Bursatella are in aggregates and visibility is higher. The Bursatella display different behavior patterns depending on the time of day. During early morning, they are found in stationary aggregates ranging from 2-12 specimens. Two forms of reproductive behavior- copulation and egg laying - are predominant. Three to four hours after sunrise, these groups disperse and the animals spend the day as mobile individuals or pairs. Emission of fecal pellets (1-3 per minute) suggests that animals are engaged in a high level of feeding during the day. During the two to three hours following sunset, the animals reassemble. Based on these observations, it is currently postulated that the animals feed during the day and engage in reproductive behaviors during the night. Under the guidance of Steve Jury, students are undertaking the completion of the ethogram for Bursatella as part of the course. Other aquatic species found in the tropical waters off Puerto Rico being examined in the course are the spiny lobster Panulirus argus, Aplysia dactylomela and freshwater prawn Macrobrachium rosenbergii.
From: http://www.neurobio.upr.clu.edu/neuroethology-98/field.htm.

I also found a couple of useful references on an associated page http://www.neurobio.upr.clu.edu/neuroethology-98/faculty.htm:
• Ramos, L.J., Rocafort, J.L.L., and Miller, M.W. (1995) Behavior patterns of the aplysiid gastropod Bursatella leachii in its natural habitat and in the laboratory. Neurobiol. of Learning and Memory, 63: 246-259.
• Miller, M.W. (1997) A cellular approach to the study of complex natural behavior patterns in the ragged sea hare (Bursatella leachii), a marine invertebrate indigenous to Puerto Rico. Puerto Rico Health Sci. J., 16: 23-36.

Concerning your question about testing this behaviour in an aquarium. This type of behaviour, where an animal changes what it is doing at regular intervals, is often triggered by an internal 'body clock'. It is called an endogenous rhythm. The simplest expression of this is seen in the many animals that sleep at night and wake during the day. The 'clock' is based in the brain and its timing is kept accurate by the light/dark - day/night cycle. In many marine animals the timing of their internal rhythms is complicated by the need to respond to the tidal cycle as well. Without the constant reinforcement of both the day/night cycle and the tidal cycle their rhythms can become seriously messed up.

I remember as a student keeping the herbivorous bubble-shell Haminoea zealandiae in two aquaria. Initially the animals in both tanks would stay buried in the sandy mud at the same time the tide would be covering their natural habitat, and would be out crawling around on top of the sandy mus in the aquaria when it was low tide outside. The slugs were in tanks where they were continually under water. Over a period of about 3 weeks the match between the tidal cycle and their tank rhythm disappeared and instead their rhythm became synchronised with the day/night cycle. Surprisingly though, in one tank they all emerged from the mud at about 4 pm and in the other tank they all buried themselves at 4 pm. I can't say much about this as it was just an interesting observation rather than a controlled experiment. I suspect if you tried to test the rhythms of Bursatella in an aquarium, it would be hard to provide a 'natural' environment. If they didn't act in the same way they are reported to do in the field, then you wouldn't know whether the original observations were wrong, or whether your experimental setup was.

Thanks again for telling us about the Puerto Rico website.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Mar 11). Comment on Bursatella leachii - behaviour by James. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/3919

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