C . Avila et al. J. Exp. Mar. Biol. Ecol. 252 2000 27 –44
33
Fig. 4. Feeding deterrence tests of mantle pieces, papillae, and crude extracts at natural concentrations of B .
hodgsoni, using the seastar O . validus as predator. Results from the Fisher’s exact test are indicated with P
values; n.s., not significant; T, treatment; C, control.
This experimental design was similar to that used by McClintock and Baker 1997b who placed food pellets in the ambulacral groove half way between the mouth and the
tip of the arm and considered movement of the pellet to the mouth and extrusion of the cardiac stomach a positive feeding response. While these investigators followed the
pellets for about 20 min, we carried out our tests for 24 h, since we observed that seastars could sometimes ingest or reject food after a few hours. We considered the food
item rejected when physical contact between the seastar and the food item ceased. Seastars were observed during the first 45 min, and then checked every 2–3 h up to 24 h
to observe whether food items were completely eaten, were still in contact with the seastars, or rejected. As in McClintock and Baker 1997b, we analyzed the data by
using a Fisher’s exact test Sokal and Rohlf, 1981 to determine significant differences between control and experimental treatments.
3. Results
A total of 40 specimens of Bathydoris hodgsoni were collected in different areas of the Weddell Sea at different depths Fig. 1, Table 1. Length and wet weight were
34 C
. Avila et al. J. Exp. Mar. Biol. Ecol. 252 2000 27 –44
Fig. 5. Feeding deterrence tests of the different fractions obtained from the ethereal extract of the mantle of B .
hodgsoni at natural concentrations, using the seastar O . validus as predator. Below fraction number the main
components of the fractions are indicated. Results from the Fisher’s exact test are indicated with P values; n.s., not significant; T, treatment; C, control.
recorded for several specimens Table 2; the use of specimens is also indicated there chemical analysis, diet or feeding tests. Qualitative stomach content analysis indicated
that the individuals examined had been feeding mainly on crinoids, sponges, alcyonarians and gorgonarians Table 3.
3.1. Location of hodgsonal As previously reported, B
. hodgsoni possesses the sesquiterpene hodgsonal Fig. 3; Iken et al., 1998. Hodgsonal is located only in the external body tissues of individuals
from different areas Fig. 1, and no differences in its concentration were detected by TLC among the different external body sections gills, foot and dorsal mantle.
Similarly, no differences in concentration of hodgsonal between the dorsal papillae and the rest of mantle tissue were detected by calibrated quantitative TLC. Several
specimens studied separately yielded similar percentages of hodgsonal Tables 4 and 5, ranging from 0.05 to 0.15 mantle dry mass Table 5.
3.2. Feeding deterrence tests Mantle pieces, mantle ethereal extract and papillae caused significant feeding
deterrence in Odontaster validus P , 0.05, Fig. 4. However, the ethereal extract of the
C . Avila et al. J. Exp. Mar. Biol. Ecol. 252 2000 27 –44
35
Fig. 6. Feeding deterrence tests for hodgsonal at different concentrations 0.05–1, using the seastar O .
validus as predator. Results from the Fisher’s exact test are indicated with P values; n.s., not significant; T, treatment; C, control.
viscera as well as the butanolic extracts of mantle and viscera were not deterrent against O
. validus P . 0.05 in the three experiments at natural or higher two-fold con- centrations Fig. 4.
The ethereal extract of the mantle of a single individual was further fractionated by column chromatography, and the different fractions obtained were tested for feeding
deterrence against O . validus. The fractions containing high R compounds fr. 1; 1.5
f
mg, fatty acids fr. 2; 4.6 mg, sterols fr. 3; 11.6 mg, and low R compounds fr. 5;
f
5.9 mg were not deterrent in O . validus tests P.0.05 for all tests at natural or higher
concentrations Fig. 5. The crude fraction containing hodgsonal fr. 4 yielded 5.4 mg. This was further
purified to yield 1 mg of pure hodgsonal. Feeding deterrence against O . validus was
tested by preparing krill with hodgsonal at five concentrations ranging from 0.05 to 1 of dry mass. All except the lowest concentration 0.05 caused significant feeding
deterrence in O . validus Fig. 6.
4. Discussion
