| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Boston University Marine Program, Marine Biological Laboratory, Woods Hole, Massachusetts 02543
1 Xavier University, Cincinnati, OH 45207.
Odor plume tracking behavior has been studied mostly in animals with bilateral chemoreceptor organs, which permit spatial comparison, a mechanism basic to locating an odor source (1). Marine snails have a single olfactory organ that samples water entering through the siphon (2). We expected that the siphon of such animals would swing from side to side, effecting bilateral sampling. We were interested in seeing if this animal could become a beneficial model for the study of spatial odor sampling.
Whelks (subfamily Busyconinae) are large marine neogastropod snails that prey upon live bivalve molluscs but will scavenge when carrion is available. We tested two sympatric species of the Busyconinae: the channeled whelk Busycotypus canaliculatus tends to be nocturnal, whereas the knobbed whelk Busycon carica does not show a preferred active time (3). Busycotypus also moves at a faster rate and preys upon more active bivalves (4).
Whelks have several sensory organs. Bilateral tentacles contain mechanoreceptors and chemoreceptors; eyes are located at their base (5). The siphon supplies water and its chemical contents to gills and the osphradium, the major chemoreceptor organ. Whelks can detect waterborne odors from potential prey, predators, and conspecifics (5,2). Because odor travels via water currents, whelks depend on hydrodynamic factors, especially currents and turbulence, which influence their ability to orient (2,5,6).
Although whelks have a wide range of prey, pieces of horseshoe crab (Limulus polyphemus) have been overwhelmingly successful as a bait in whelk traps (7). Research is in progress to determine the compounds responsible for the whelk’s attraction to female Limulus and to produce an artificial bait (Nancy Targett, pers. comm.). In addition to our basic scientific goals, we were also interested in contributing to bait development. Therefore, we measured the responses of channeled and knobbed whelks in a flume to various target sources introduced upstream. The target sources were dead Limulus bodies, Limulus hemolymph, dark-painted cement casts of Limulus, 5% mussel juice (from Geukensia demissa, a food source readily consumed in the laboratory), seawater, and the non-flowing tubing, nozzle, and lead weight of the liquid stimulus introduction system. The flume was large (dimensions: 10 m x 2 m x 0.5 m) and had a constant background flow of 7 cm s-1. Target sources were used individually and in combinations; the liquid stimuli were introduced onto the bottom of the flume, via gravity flow, through a 5-mm-diameter nozzle (flow velocity 40 ml/min, Reynolds number = 100). In each trial, five whelks were placed 1 m downstream from the target sources, and responses were recorded on videotape for at least 45 min. Paths of both the siphon tip and the center of the shell were digitized at 1 Hz. From these data, crawling velocity, heading angles, and turn angles were determined. "Orientation" was defined as a path ending or passing within one body length from the source. "Non-orienting" whelks responded by moving from their starting position but did not pass close by the source. "Zigzag" was defined as locomotion with turn angles greater than 45° over more than 50% of the path; all other tracks were "smooth."
In general, responsiveness to any source was low (range 0.00%–19.23%) when compared to that of Illyanassa obsoleta responding to Mytilus edulis (range 60%–100%) (8). Over the course of the summer, the activity of all the whelks tended to decrease (ANOVA, F = 3.17, P = .058). This trend may have been due to increasing temperature (20 to 23.5 °C) or to the natural decrease in feeding that occurs May to September during the mating season (9). Whelks may show stronger feeding attraction and activity in their natural environment, during the winter, or at night.
Channeled whelks responded and oriented more often than knobbed whelks (ANOVA, F = 6.48, P = .018) (Fig. 1A). Knobbed whelks zigzagged more than channeled whelk. Because channeled whelks oriented more often (
2 = 7.5, P = .0062), but zigzagged less (2 = 6.29, P = .012), zigzag may not be characteristic of orientation behavior (Fig. 1A). Zigzag was not an individual characteristic, because zigzagging whelks also exhibited smooth behavior. We limited further analysis to the responses of orienting channeled whelks. When these whelks approached a target source, half of them exhibited no change in velocity, and the other half decreased their speed or (in rare cases) stopped near the source. Only two zigzagged, and these stopped or decreased in speed near the source. Zigzagging occurred in similar proportions in response to control conditions, food, and combination targets; this behavior, to our surprise, is thus unlikely to be a response to chemical stimuli.
|
2 = 12.76, P = .0004) and hemolymph (2 = 10.40, P = .0013)—but, to our surprise, not seawater (2 = 2.14, P = .14)—elicited significantly fewer responses. In fact, the flowing seawater control elicited more responses than mussel juice (2 = 4.72, P = .03) and hemolymph (2 = 5.81, P = .016) (Fig. 1B). Limulus cast elicited no responses (Fig. 1B), showing that attraction to Limulus bodies was not due to their hydrodynamic (wake-producing) properties. Lower responses to chemical sources (hemolymph and mussel juice) than to controls (seawater and no flow) suggest, if anything, that these presumed attractants were actually repellents. In conclusion, the evidence indicates behavioral differences between channeled and knobbed whelks. It also demonstrates that Limulus bodies are an attractive target for channeled whelks, whereas Limulus hemolymph and the hydrodynamic wake are not attractive. Because orienting paths most often showed a smooth character, the use of bilateral chemoreceptive organs, such as the tentacles, should be considered.
Supported by the National Science Foundation Research Experience for Undergraduates at the Boston University Marine Program (OCE 0097498). We thank Gabriele Gerlach for statistical advice and the laboratory of Robert Barlow, Jr. for the loan of the Limulus cast.
Literature Cited
This article has been cited by other articles:
|
|
 |
|
  J.W.S. Scolding, C.A. Richardson, and M.J. Luckenbach Predation of cockles (Cerastoderma edule) by the whelk (Buccinum undatum) under laboratory conditions J. Mollus. Stud., November 1, 2007; 73(4): 333 - 337. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
= .01). (B) Responses of orienting channeled whelks (Busycotypus) to control and experimental sources, presented in order of responsiveness. Dead Lim, dead, punctured and bleeding Limulus body; SW, seawater control; No Flow, fluid source nozzle and lead weight only; MJ, mussel juice; Hemo, Limulus hemolymph; Lim cast, dark painted cement cast of Limulus. "a" and "b" denote significant differences (