Magel et al,: Activity in the pallial nerve of Busycon canca and Busycotypus cano/iculotum 



489 



fy'^^''^ Horseshoe crab eggs 



m^mppm Hard clam tissue 



Knobbed whelk 



2.1 -y Channeled whelk 

 / 



1.6  

 1.4  

 1.2  

 1.0 



0.8 



14 



i. 



1. 



ii 



P 



^1 



i 



FSW 1:10' 



1;10 



Stimulus dilution 



13 

 * 



PI 



i 

 I. 



1 



1:10' 1:10^ 



Figure 3 



Mean responses (±95'X CI) of knobbed (Busycon carica) and channeled (Busycotypus canaliculatum) whelks 

 to odorant solutions prepared from horseshoe crab (Limulus polyphemus) eggs and hard clam (Mercenaria 

 mercenaria) tissue. FSW refers the use of filtered sterilized water in place of an odorant solution. The 

 data are the ratio of integrated activity in the pallial nerve recorded during exposure of the osphradium 

 to integrated activity in the pallial nerve recorded before exposure to the odorant solutions. The numbers 

 of individuals used in each trial in) are shown above each bar. 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'if confidence interval). The solid line indicates a ratio of integrated 

 activity value = 1.0. 



odorant solution). The ratios of nerve activities during 

 application of the odorant solutions to that recorded 

 immediately before application were calculated to test 

 for the presence of responses. This technique reduces 

 the influence of interanimal variability, as well as the 

 inherent variability associated with the use of suction 

 electrodes iStys et al., 1991). 



Data sets were screened for normal distributions with 

 the Anderson-Darling test (Minitab version 14.20.2, 

 Minitab Inc., State College, PA) and all passed. Data 

 were averaged across individuals for each species of 

 whelk, and the standard errors (SE) and 95% confidence 

 intervals (CIs) were calculated. A significant response 

 to an odorant solution was deemed to have occurred if 

 the 95% CI of the mean ratio of integrated nerve activ- 

 ity did not overlap 1.0. This was equivalent to using 

 a two-tailed t-test with P < 0.05 taken as the level of 

 significance. 



Results 



The pallial nerve typically showed spontaneous activity, 

 although nerve activity clearly increased as the concen- 

 tration of a detectable odorant solution in the osphra- 

 dium chamber reached maximal concentration (Fig. 2). 

 Once the flow of FSW was resumed (90 seconds after 

 stimulus onset), the concentration of odorant solution in 

 the osphradium chamber decreased (Fig. IB) and nerve 



activity diminished (Fig. 2). Nerve activity generally 

 returned to near prestimulus levels within the record- 

 ing period (Fig. 2). 



Neither species responded to FSW alone (Fig. 3). 

 Odorant solutions extracted from horseshoe crab eggs 

 with FSW elicited a significant increase in pallial nerve 

 activity in both knobbed and channeled whelks at a 

 dilution of 10^:1, but not at any of the higher dilution 

 ratios (i.e., lower concentrations) (Fig. 3). Odorant so- 

 lutions extracted from hard clam tissue also elicited a 

 significant increase in pallial nerve activity of knobbed 

 whelk at the lO'^il dilution ratio, but not at higher di- 

 lutions (Fig. 3). This solution was not tested on chan- 

 neled whelk. In contrast to odorant solutions prepared 

 from horseshoe crab eggs by using FSW, odorant solu- 

 tions containing horseshoe crab hemolymph generated 

 a species-specific pattern of responses. These elicited 

 significant increases in pallial nerve activity in knobbed 

 whelk at both 100:1 and 133:1 dilutions, whereas chan- 

 neled whelk did not respond to any of the four concen- 

 trations tested (Fig. 4). 



Odorant solutions prepared from horseshoe crab eggs 

 by using 50 mM Tris buffer solution were tested only on 

 channeled whelk (Table 1). This stimulus elicited a sig- 

 nificant increase in pallial nerve activity at a dilution 

 of 10'^:1, but not at higher dilutions (Fig. 5) — a result 

 identical to that recorded in channeled whelk with the 

 use of horseshoe crab eggs odorant solutions prepared 

 with FSW (Fig. 3). Channeled whelk did not respond 



