Winsor H. Watson

Characterization and distribution of FMRFamide immunoreactivity in the rat central nervous system

FMRFamide immunoreactive material (irFMRFamide) was studied in rat brain and gastrointestinal tract. Highest irFMRFamide concentrations were found in tissues of the gastrointestinal tract and, in the brain, highest concentrations were found in the hippocampus, midbrain, brainstem and hypothalamus. High pressure liquid chromatographic characterization of irFMRFamide demonstrated that the immunoreactive material in brain, pancreas and duodenum was different from molluscan FMRFamide but it was also distinct from any known neuropeptide.

Lobster trap video: in situ video surveillance of the behaviour of Homarus americanus in and around traps

A lobster-trap video (LTV) system was developed to determine how lobster traps fish for Homarus americanus and how behavioural interactions in and around traps influence catch. LTV consists of a low-light camera and time-lapse video cassette recorder (VCR) mounted to a standard trap with optional red LED arrays for night observations. This self-contained system is deployed like a standard lobster trap and can collect continuous video recordings for >24 h. Data are presented for 13 daytime deployments of LTV (114 h of observation) and 4 day and night deployments (89 h of observation) in a sandy habitat off the coast of New Hampshire, USA. Analyses of videotapes revealed that traps caught only 6% of the lobsters that entered while allowing 94% to escape. Of those that escaped, 72% left through the entrance and 28% through the escape vent. Lobsters entered the trap at similar rates during the day and night and in sandy and rocky habitats. Lobsters generally began to approach the trap very shortly after deployment, and many appeared to approach several times before entering. These data confirm the results of previous laboratory-based studies in demonstrating that behavioural interactions in and around traps strongly influence the ultimate catch.

The neuropeptide proctolin acts directly onLimulus cardiac muscle to increase the amplityde of contraction

The pentapeptide proctolin increases the amplitude of contraction but not heart beat frequency of the isolated heart of Limulus polyphemus. It acts directly on the heart muscle and has no effects on the neurones of the cardiac ganglion or on the cardiac neuromuscular EJPs. A peptide with molecular weight, enzymatic susceptibilities and physiological effects similar to those of proctolin occurs in the Limulus cardiac ganglion. It is suggested that proctolin, or a family of proctolin-like peptides, may modulate muscle contraction in more than one subphylum of the Arthropoda.

Daily Patterns of Locomotion Expressed by American Lobsters (Homarus Americanus) in Their Natural Habitat

Abstract The local movements and activity patterns of American lobsters, Homarus americanus, were monitored inside a 50 m by 50 m underwater enclosure (mesocosm) using ultrasonic telemetry. Forty-four lobsters of both sexes, ranging in size from 62 to 93 mm in carapace length, were continuously tracked for 2-10 days in 2002 and 2003. As a population, the movement rate of lobsters depended on time of day, as defined by dawn, day, dusk or night. Lobster movement rates were significantly higher during night and dawn than day and dusk hours. Movement rates did not differ by lobster sex, size or between years of the study. The effect of time of day differed between lobsters, and there was considerable variability in the time of day when individual lobsters were most active. Thirty lobsters moved significantly more during the night, five moved significantly more during the day, and nine did not move significantly more during the day or night. Therefore, while there was a general tendency for lobsters in this study to be more active at night, certain factors in their natural habitat modulated this nocturnal bias, which led to a tremendous amount of variability in their daily patterns of behavior.

Presence and distribution of immunoreactive and bioactive FMRFamide-like peptides in the nervous system of the horseshoe crab, limulus polyphemus

FMRFamide immunoreactivity was detected in all regions of the Limulus nervous system, including the brain (6.5 +/- 0.6 pg FMRFamide/mg), cardiac ganglion (2.06 +/- 0.67 pg FMRFamide/mg), and ventral nerve cord (5.8 +/- 0.7 pg FMRFamide/mg). The distribution of immunoreactive FMRFamide (irFMRFamide) was mapped by immunofluorescence and the distribution corresponded to regional RIA data. A good proportion of the CNS and cardiac ganglion neuropile contained irFMRFamide, and fluorescent cell bodies were observed in several areas. High performance liquid chromatography (HPLC) was employed to separate and characterize the FMRFamide-like peptides from extracts of Limulus brains. HPLC fractions were analyzed using coincidental radioimmunoassay and bioassay (the radula protractor muscle of Busycon contrarium). There appear to be at least three FMRFamide-like peptides in the Limulus brain, including one similar to clam FMRFamide. FMRFamide acts on Limulus heart in a biphasic manner at relatively high concentrations (10(-5)M), but has no effect on the activity of the isolated ventral nerve cord. These data suggest that in Limulus FMRFamide-like peptides are acting as neurotransmitters, or neuromodulators.

The behavior of lobsters in response to reduced salinity

Abstract Two experiments were conducted to measure the behavioral responses of lobsters, Homarus americanus (Milne-Edwards), to reductions in salinity. In the first experiment animals were placed in a 3 ft diameter tank that was divided in half by plastic mesh. Spontaneously active lobsters were able to move between the two halves of the tank by passing through either of two conduits. The conduits were equipped with optical sensors to monitor the passage of animals, and a perfusion system to control the salinity of the area in, and around, the conduit. When the salinity in the vicinity of both conduits was the same (28–32 ppt), lobsters exhibited no preference for either conduit. However, when the salinity in one of the conduits was lowered, lobsters preferred to pass through the high salinity (20–25 ppt) conduit rather than the one with low salinity (10–15 ppt). In addition, females appeared to be more selective in their preference and exhibited higher overall activity than males when exposed to reduced salinity. In the second experiment, individual lobsters were placed in a shelter at one end of a long seawater table and exposed to seawater of gradually decreasing salinity. The salinity required to cause a movement out of a shelter, i.e. an avoidance response, was recorded. On average, lobsters first ventured small distances ( one body length) when levels approached 12.62 ppt ± 1.59. Although it was not statistically significant, females again seemed to be either more sensitive to salinity or found it more aversive, because they tended to initiate movements at salinities greater than those required to influence males. These behavioral data indicate that: 1. (1) adult lobsters are capable of detecting changes in salinity which are comparable to the levels found during natural fluctuations in coastal bays and estuaries; 2. (2) when exposed to low salinity of sufficient magnitude, they attempt to avoid it, and; 3. (3) females appear to be more sensitive to drops in salinity and/or they find it more aversive. Previous studies have demonstrated that estuarine lobster populations are dominated by males and that there are seasonal migrations of lobsters into, and out of, estuaries. We conclude that the behavioral responses of male and female lobsters to low salinity may determine, in part, the distribution and movements of lobsters in estuarine habitats.

Thermosensitivity of the lobster, Homarus americanus, as determined by cardiac assay.

It is generally accepted that crustaceans detect, and respond to, changes in water temperature, yet few studies have directly addressed their thermosensitivity. In this investigation a cardiac assay was used as an indicator that lobsters (Homarus americanus) sensed a change in temperature. The typical cardiac response of lobsters to a 1-min application of a thermal stimulus, either warmer (n = 19) or colder (n = 17) than the holding temperature of 15 degrees C, consisted of a short bradycardia (39.5 +/- 8.0 s) followed by a prolonged tachycardia (188.2 +/- 10.7 s). Lobsters exposed to a range of rates of temperature change (0.7, 1.4, 2.6, 5.0 degrees C/min) responded in a dose-dependent manner, with fewer lobsters responding at slower rates of temperature change. The location of temperature receptors could not be determined, but lesioning of the cardioregulatory nerves eliminated the cardiac response. Although the absolute detection threshold is not known, it is conservatively estimated that lobsters can detect temperature changes of greater than 1 degree C, and probably as small as 0.15 degrees C. A comparison of winter and summer lobsters, both held at 15 degrees C for more than 4 weeks, revealed that although their responses to temperature changes were similar, winter lobsters (n = 18) had a significantly lower baseline heart rate (34.8 +/- 4.4 bpm) and a shorter duration cardiac response (174 s) than summer lobsters (n = 18; 49.9 +/- 5.0 bpm, and 320 s respectively). This suggests that some temperature-independent seasonal modulation of cardiac activity may be occurring.

The effects of reduced salinity on lobster (Homarus americanus Milne-Edwards) metabolism: implications for estuarine populations

Abstract During periods of substantial freshwater runoff, lobsters that inhabit estuaries, such as the Great Bay Estuary in NH, are exposed for several days to weeks to seawater that is diluted as low as 10 ppt. To assess the physiological stress imposed by these conditions, we measured the oxygen consumption, heart rate, ventilation rate and hemolymph osmolarity of lobsters while sequentially exposing them, for 24-h periods, to seawater of 20, 15, and 10 ppt. Measurements of hemolymph osmolarity confirmed previous results which demonstrated that at salinties below 20 ppt lobsters are limited osmoregulators; allowing their hemolymph osmolarity to drop as the environmental salinity is reduced, but always maintaining it higher than the ambient osmolarity. All animals exposed to 10 ppt, at 15 °C, were capable of surviving for at least 72 h. There was a nearly linear increase in oxygen consumption, heart and scaphognathite rates in animals exposed to dilute seawater, with almost a twofold increase in metabolic rate when animals were moved from 20 to 15 to 10 ppt. At the lowest salinity tested (10 ppt) the average oxygen consumption was higher for females than for males. We conclude that at low salinities the energetic demands of osmoregulation are greater for females than males, and for both sexes the physiological stress imposed may determine, in part, their distribution and/or movements in estuarine habitats.

Circatidal and Circadian Rhythms of Locomotion in Limulus polyphemus

The nocturnal increases in the sensitivity of the lateral eye of Limulus polyphemus, the species of horseshoe crab found along the Atlantic coast, have been firmly established as being controlled by an endogenous circadian clock (1, 2, 3) located in the brain (4). Virtually nothing is known, however, about the control of the animal’s behavioral rhythms of mating and spawning that are observed in the intertidal zone during high tides in late spring (5, 6, 7). Many other marine species, especially intertidal crabs, exhibit similar rhythmic behaviors that have been demonstrated to be under the control of endogenous clocks that are circatidal (8, 9, 10, 11, 12), circadian (10, 12), or both. While there is some evidence that the activity of juvenile horseshoe crabs is primarily nocturnal (13, 14), and possibly controlled by a circadian clock (14), we know of no published work showing that locomotor activity in the adult is endogenously controlled on either a 12.4-h (circatidal) or 24-h (circadian) basis. We report here that locomotor activity in adult individuals of L. polyphemus is endogenously modulated on both a circatidal and a circadian basis and that when the animals are subjected to a light-dark (LD) cycle, most activity occurs at night. The locomotor activity of individual adult horseshoe crabs was recorded using activity chambers located in recirculating aquaria. Animals were exposed to three conditions: a 12:12 LD cycle, at 11–14 °C (“fall” conditions, LD1), a 14:12 LD cycle, at 17–21 °C (“summer” conditions, LD2), and constant darkness (DD). Typical records of the locomotor activity of three horseshoe crabs exposed to these three different photoperiods are presented in Figure 1. Circatidal rhythms were observed in all animals. While significant activity rhythms (15) in the tidal range (12.4 h) were found in only 3 of 6 animals (tau 12.83 0.78 h [mean SEM]) during LD1, in LD2, significant tidal rhythms (12.2 0.1 h) were observed in all animals. In some cases in LD2 (4 of 6 animals), clear free-running rhythms were sometimes apparent, (Fig. 1; middle, bottom panels), while in other cases the activity appeared to synchronize to the LD cycles (Fig. 1; top). In DD, circatidal rhythms (12.6 0.2 h) were found in 5 of 6 animals (Fig. 1; all panels). Most animals (5 of 6 in LD1; 6 of 6 in LD2) exhibited significant rhythms in the circadian range (tau 24.29 0.14 h). Periodogram analyses (15) and visual inspection indicated that 5 of the 6 animals tested synchronized their activity to the initial 12:12 LD cycle (LD1). The single animal that did not thus synchronize had a very low level of activity. Significantly more activity occurred during the dark phase than the light phase in 4 of 6 animals (Fig. 1; top and bottom [but not middle] panels). The average period (tau) for these animals in the daily (24-h) range in LD1 was 24.12 0.09 h. Upon subsequent exposure to “summer” conditions (LD2), 3 (of 6) animals remained synchronized to the LD cycle (Fig. 1; top panel). In others (2 of 6), this apparent synchronization was not stable (Fig. 1; middle, days 10–18 and days 29–42) and, in still another animal, the synchronization, if any, was unclear (Fig. 1; bottom). Animals that both synchronized and showed a clear onset of activity initiated their activity a significant amount of time (1.7 0.1 h; P 0.005) before the lights went out during LD2 but not LD1 (1.1 0.5 h; P 0.15). Significantly more activity occurred during D versus L periods in 3 of 6 animals (Fig. 1; top panel only). In constant darkness (DD), all animals also expressed significant circadian rhythms (25.27 0.69 h; Fig. 1, all panels). In addition, the activity patterns of 3 of 6 animals in DD exhibited evidence of entrainment based on the similarity of phasing with the previous LD cycle (Fig. 1; top, middle). L. polyphemus was significantly more active overall during LD2 than during LD1 and DD (P 0.03). Neither circatidal (P 0.78) nor Received 12 February 2004; accepted 7 June 2004. * To whom all correspondence should be addressed. E-mail: chrisc@mail.plymouth.edu Reference: Biol. Bull. 207: 72–75. (August 2004)

Swimming Behavior of the Nudibranch Melibe leonina

Swimming in the nudibranch Melibe leonina consists of five types of movements that occur in the following sequence: (1) withdrawal, (2) lateral flattening, (3) a series of lateral flexions, (4) unrolling and swinging, and (5) termination. Melibe swims spontaneously, as well as in response to different types of aversive stimuli. In this study, swimming was elicited by contact with the tube feet of the predatory sea star Pycnopodia helianthoides, pinching with forceps, or application of a 1 M KCl solution. During an episode of swimming, the duration of swim cycles (2.7 ± 0.2 s [mean ± SEM], n = 29) and the amplitude of lateral flexions remained relatively constant. However, the latency between the application of a stimulus and initiation of swimming was more variable, as was the duration of an episode of swimming. For example, when touched with a single tube foot from a sea star (n = 32), the latency to swim was 7.0 ± 2.4 s, and swimming continued for 53.7 ± 9.4 s, whereas application of KCl resulted in a longer latency to swim (22.3 ± 4.5 s) and more prolonged swimming episodes (174.9 ± 32.1 s). Swimming individuals tended to move in a direction perpendicular to the long axis of the foot, which propelled them laterally when they were oriented with the oral hood toward the surface of the water. The results of this study indicate that swimming in Melibe, like that in several other molluscs, is a stereotyped fixed action pattern that can be reliably elicited in the laboratory. These characteristics, along with the large identifiable neurons typical of many molluscs, make swimming in this nudibranch amenable to neuroethological analyses.