T. Teyke et al., ORIENTATION OF APLYSIA-CALIFORNICA TO DISTANT FOOD SOURCES, Journal of comparative physiology. A, Sensory, neural, and behavioral physiology, 170(3), 1992, pp. 281-289
The behavior of the marine mollusc Aplysia was examined under differen
t experimental conditions designed to determine the food searching str
ategy of the animals. In a small, open field tank with still water, th
e animals took an average of 42 min to find a piece of seaweed, even t
hough the stimulus was never located more than 30 cm away from the ani
mal. Observations of the animals indicated that their search was not d
irected, without a clear tendency towards the food, and during the cou
rse of a search, they often crawled through most of the area of the ta
nk. The search time, the distance travelled, and the strategy of the s
earch of the animals was similar for different types of seaweed. If an
imals were aroused into activity by the presence of seaweed extract, t
he time for them to contact a piece of odorless glass fiber paper in t
he open field was not significantly different than that for a piece of
seaweed. The probability at which the animals contacted the seaweed,
as a function of the distance travelled, resembled the detection proba
bility determined according to a theory of random search. We thus prop
ose that the aroused animals move in a random pattern until they are v
ery close to the food. This strategy can be advantageous in still wate
r since chemicals do not provide distinct gradients that can serve as
cues for chemotactic orientation from distances greater than a few cen
timeters from the source. In a Y-maze in still water, Aplysia did not
perform above chance in selecting the arm that contained the seaweed.
In streaming water, the animals entered the arm that contained seaweed
significantly above chance only if a large piece of seaweed was used,
so as to provide a very strong stimulus. Similarly, presentation of a
high concentration of glutamate or a high concentration of seaweed ex
tract to one side of the animal could evoke turning towards the stimul
us. In the Y-maze, animals that repeatedly entered and exited both arm
s before making a choice, performed better than those that went direct
ly into one arm. We conclude that chemical food stimuli can evoke dire
cted orientation only when the animal is very close to the stimulus (w
ithin a few centimeters, at most). For Aplysia, the role of distant ch
emical stimuli may not be to guide their orientation, but rather to ev
oke the food-induced arousal state. In this behavioral state, several
behaviors, such as locomotion are altered, and these changes may provi
de the basis for locating food from a distance.