The Effects of Dominant Lobster Smell on Heart Rate in Homarus americanus

Fighting Dominance in Homarus americanus is established by display or fighting, and is maintained by display. One of the chemical displays during fighting is the lobsters directing streams of urine at each other. (Atema and Voigt, 1995) Atema and Karavanich (1991) found that memory of a specific opponent lasts for about a week when the two contestants are housed in isolation. Blocking or catheterizing neophores and lesioning antennules shows that this memory is based on chemical signals mediated by olfaction Atema and Voigt (1995) have shown this memory is based on chemical signals in urine mediated by olfactory

Scrivener’s physical pathway of winners; (1971) - antenna point, approach, meral spread, follow, rush, scissor, meral spread, antenna point And losers; -antenna point, back, abdomen flex, back antenna point Behavior and Physiology In lobsters, it has been found that startle responses can cause ceases in heart rate for a few seconds, probably in response to neural inhibition of the cardiac ganglion (McMahon, 1999) J. L. Wilkens, L. A. Wilkens and McMahon (1973) have found that a startle response in crabs can be caused by a variety of mechanical and chemical stimuli

Atema and Voigt (1995) have described stimulatory effects of food extracts as well as tank water from aquaria containing prey or conspecifics However, effects of heart rate from tank water of conspecifics has never been examined before The purpose of our experiment was to determine if chemo-receptive cues from a dominant lobster could alter the heart rate of the subordinate lobster

We believe chemical cues from the dominant lobster, without being seen, will cause an increase in heart rate of the subordinate

Materials and Methods Animals Two lobsters were chosen to fight, one appeared passive and one appeared dominant after observation. A third lobster was isolated visually and chemically from the other two. Fighting Procedure The bands were taken off the lobsters They were left to fight for approximately 15 minutes There were only two brief altercations The dominant chased off the passive both times

Surgery Wires were placed in the carapace to monitor heart rate The wires were hooked up to an impedance converter Powerlab was used to monitor the lobster’s heart rate Experimental procedure Two lobsters, the control and the loser of the fight, were left in boxes in a separate tank, isolated visually and confined They were exposed to a constant flow of water through a tube that was aimed at the antennules.

The dominant lobster was isolated in a small separate holding tank for 1 day. The water was then introduced during certain times of the experiment at different amounts (mls). The water was added through a funnel directed into the tubes leading to the lobsters Heart rate was monitored before and after the dominant lobster water was added and analyzed using a student t-test in Statview (Abacus Concepts)

Results

Fig. 1 Normal Heart Rate Before Stimulus

Fig. 2 Bradycardia After Stimulus Water Reached Lobsters

Fig. 3 Fig. 3 represents the heart rate before the stimulus was introduced and after the stimulus was introduced in the control lobster t(9)=1.961,p=.0815.

Fig. 4 shows the mean heart beat of the losing lobster before and after stimulus was introduced t(9)=.024,p= There were no responses to the stimulus and heart rate remained virtually identical before and after stimulus was introduced.

Discussion We found that there was no effect of dominant lobster water on heart rate in the lobster who lost the fight. However, although not significant, there seemed to be an affect of dominant lobster water on the isolated lobster. Behavior and Physiology J.L. Wilkens, L. A. Wilkens and Mcmahon (1973) have found that a startle response in crabs can be elicited by a wide variety of chemical and mechanical stimuli oHowever, Wilkens et al found that habituation can occur to frequently repeated stimuli oIn lobsters, it has been found that startle responses can cause ceases in heart rate for a few seconds, probably in response to neural inhibition of the cardiac ganglion (McMahon, 1999) o We witnessed Bradycardia, which was visible in the first two trials, and then decreased in subsequent trials which were conducted within 5-20 minutes of each other.

Wilkins, et al also suggested that this startle response can result in arythmia in order to conceal themselves around a potential predator oWe originally thought that when we added lobster smell the heart rate would increase, to get oxygen to the muscles and get blood flowing in order to prepare to defend itself. oThe lobster that did fight the dominant one had no reaction at all when the smell was introduced Possible Improvements A larger n should have been used, two individuals was not enough to get significant results It could have helped to have the lobsters completely isolated in different tanks throughout the whole experiment

The study done by Kravitz published in 1999 suggests that serotonin may be a very important hormone contributing to aggression A possible follow up of our experiment could be to measure the levels of serotonin in the different lobsters tested, or to inject serotonin in the submissive lobster and see what difference that makes in heart rate or behavior