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Fishery Bulletin 105(4) 



to the Tris buffer solution alone (Fig. 5). Nor did they 

 respond to either of the molecular weight fractions (>3 

 kDa nor <3 kDa) prepared from the horseshoe crab egg 

 odorant solutions by ultrafiltration at any concentration 

 tested (Fig. 5). When recombined, the molecular weight 

 fractions again induced a response at 10^:1 dilution 

 (Fig 5). 



Discussion 



Electrophysiological techniques appear suitable for 

 determining odorant solutions that stimulate the pal- 

 lial nerve in both knobbed and channeled whelks. The 

 sustained increases in nerve activity of the pallial nerves 

 of these two species (exemplified by the results shown 

 in Fig. 2) are similar to those recorded by Bailey and 

 Laverack (1963, 1966) upon exposure of the osphradium 

 of the common whelk (Buccinuni undatum) to extracts 

 prepared from the blue mussel (Mytilus edulis). Bailey 

 and Laverack (1966) also observed extended periods of 

 increased nerve activity, which they termed "the Mytiliis 

 response." Wedemeyer and Schild (1995) demonstrated 

 similar increases in activity of the pallial nerves of the 

 pond snail (Lymnaea stagnalis) in response to expo- 

 sure of the osphradium to mixtures of amino acids, to 

 hypercapnia, and to hypoxia. The sustained activity in 



EZZZ2 Knobbed whelk 

 Y////////A Channeled whelk 



FSW 



1:400 1:200 1:133 1:100 

 Stimulus dilution 



Figure 4 



Mean responses ( ±95% confidence interval) of knobbed 

 (Busycon carica) and channeled iBusycotypus canalicu- 

 latum) whelks to horseshoe crab (Limulus polyphemus) 

 hemolymph diluted with filtered sterilized water. The 

 data are the ratio of integrated activity in the pal- 

 lial nerve recorded during exposure of the osphradium 

 to odorant solutions to intergrataed activity recorded 

 before exposure to odorant solution. The numbers of 

 individuals used in each trial are shown above each 

 bar (n). A significant response (indicated by "*") was 

 determined to have occurred when the mean ratio of 

 integrated nerve activity was significantly different 

 from 1.0 (based on the 95% CI). The solid line indicates 

 a ratio of integrated activity value = 1.0. 



the pallial nerve during odor stimulation observed in 

 knobbed and channeled whelks (exemplified in Fig. 2) 

 is also consistent with Ferner and Weissburg's (2005) 

 findings that slow moving gastropod moUusks locate odor 

 sources in turbulent flow conditions by temporally aver- 

 aging odor concentrations across a plume. In contrast, 

 the more rapid onset and offset of olfactory responses 

 (i.e., shorter temporal resolution) of the crustacean olfac- 

 tory system (Gomez and Atema, 1996) appears to hinder 

 their olfactory navigation in turbulent environments 

 (Weissburg and Zimmer-Faust, 1993, 1994). 



It is possible that increases in nerve activity in re- 

 sponse to odorant solutions also include increases in 

 proprioceptor activity resulting from odor-induced mus- 

 cular contractions. The pallial nerve appears to be a 

 sensory nerve that conveys a suite of information to 

 the circumesophogeal ganglion (Laverack and Bailey, 

 1963). The pallial nerves of whelks show a low level 

 of almost constant spontaneous activity (Fig. 2C), and 

 rapid onset and offset increases in activity associated 

 with slight spontaneous movements of the head, probos- 

 cis, or siphon (Fig. 2A). The origin of the spontaneous 

 activity is unknown, but the latter (the rapid onset 

 and offset increases in activity) are most likely due to 

 activity of axons within the pallial nerve originating 

 from proprioceptors (Laverack and Bailey, 1963). It is 

 possible, therefore, that the ultimate origin for nerve 

 activity seen during application of odorant solutions to 

 the osphradium are proprioceptors, and that these are 

 being stimulated by increased movements in response to 

 application of odorant solutions to the osphradium. This 

 does not, however, invalidate the results. Responses to 

 odorant solutions are still being recorded, albeit not 

 directly in the manner assumed. 



One of the objectives of the present project was to 

 determine whether odorant solutions prepared from 

 horseshoe crab eggs stimulated chemosensory receptors 

 in the whelk species targeted by the pot fishery. Ferrari 

 and Targett (2003) suggested the potential use of olfac- 

 tory attractants from horseshoe crab egg extracts as an 

 alternative to horseshoe crab bait. Their conclusion was 

 based on the behavioral responses of the common mud 

 snail to heat-stable proteinaceous compounds extracted 

 from horseshoe crab eggs. Because both knobbed and 

 channeled whelks respond to horseshoe crab egg odor- 

 ant solutions prepared with FSW at a 10^^:1 dilution 

 (Fig. 3), our results support their findings. Horseshoe 

 crab eggs clearly contain a compound (or compounds) 

 detectable by whelks even at low concentrations; there- 

 fore odorant solutions prepared from horseshoe crab 

 eggs need to be examined further. 



Defining chemical cues from a specific molecular 

 weight class that elicit a response in whelks may prove 

 to be difficult. Channeled whelk responded to odorant 

 solutions prepared from horseshoe crab eggs with Tris 

 buffer solution, as well as the recombined molecular 

 weight fractions (i.e., >3 kDa and <3 kDa). They did 

 not respond to either molecular weight fraction inde- 

 pendently (Fig. 5). These results imply that neither the 

 initial extraction (FSW vs. Tris buffer solution) nor ul- 



