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ALLEMAN, LANI L. (Hopkins Marine Station of Stanford University,
Pacific Grove, California). Factors Affecting the Attraction
of Acmaea asmi to Tegula funebralis (Mollusca: Gastropoda:
Prosobranchia). The Veliger
The behavioral basis of the association between Acmaea asm.
and Tegula funebralis has been investigated. The observations
indicate that A. asmi is not a
cacted by a diffusible substance.
but senses its substrate through contact with its tentacles. The
critical substance(s) on the shell are easily destroyed or dis¬
solved by ethanol and slightly removed by distilled water,
These factors are also present on Pagurus-inhabited Tegula
shells, but are not found on uninhabited shells found on the beach,
PLEASE DO NOT TYPE BELOW THIS LINt
18
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Factors Affecting the Attraction of
Acmaea asmi to Tegula funebralis
(Mollusca; Gastropoda; Prosobranchia)
by
Lani Lee Alleman
Hopkins Marine Station
Stanford University
Pacific Grove, California,350
Toctusle1.
Lani Alleman
Acmaea asmi (Middendorff, 1849) lives almost exclusively as a
commensal on the shell of Tequla funebralis (A. Adams, 1854). Pre-
vious workers found this association to be quite specific, A. asmi
preferring T. funebralis to Tegula brunnea (Philippi, 1848). Test
(1945) suggested that T. funebralis released a chemical attractant.
The source of this attractant was considered to be the shell by
Radford (1959), whereas, Eikenberry and Wickizer (1960) concluded
that both animal and shell were necessary. The following study
attempts to settle these differences and to provide further infor-
mation on behavioral and chemical aspects of this association.
Materials and Methods
Nost organisms used in this study were collected in inter-
tidal areas near Hopkins Marine Station, except for Tegula brunnea
Crmel Bag, Calig.
which was collected in the Pebble Beach area, All experiments were
run over night in pyrex dishes kept at 12-13°C in a darkroom.
Preliminary experiments showed that if no choice were offered,
Acmaea asmi would climb onto any shells tested. Therefore, to
measure relative preferences, the limpets were allowed to choose
between two different substrates. In the test five limpets were
placed in about two om of water in the center of a 24 cm pyrex pie
plate. Ten test shells were placed equidistantly around the periphery
of the plate. There were five of each type to be compared, and they
were placed alternately in the sircle.
To permit washing of the Tequla shells with various solvents,
the operculum was sealed with canning wax (Parowax). The animals
survived this sealing treatment, and most importantly, were apparently
O
Lani Alleman
unaffected by such solvents as alcohol or distilled water.
In all experiments the dishes were then placed overnight in
a darkroom at 12-13eC, and the number of limpets on the test shells
determined the following morning.
Results and Dissussion
Rodford (1959) found that the shells of Tequla funebralis were
not preferred by Acmaea asmi if the shells were boiled in alcohol
for 15 minutes. The results shown in Figure lA indicate that simple
room-temperature washing in ethanol for one hour also removes any
attractant on the shell. In this experiment the limpets were given
a choice between parowax-sealed shells washed in alcohol and control
parowax-sealed shells. In five trials (25 limpets) the control
shells attracted 90% of the limpets, while the alcohol-washed shells
attracted ten per cent.
The attractant is also partially removed by distilled water.
If sealed shells containing Tequla funebralis are washed for two
hours in distilled water and compared with normal, sealed shells,
only 253 are found on the washed shells versus 65% on the control
shells (rig. 18). (Where the total percentage does not equal 1007,
the difference represents those animals not found on any shell.)
However, distilled water washing is not as effective as alcohol
washing. As seen in Fig. 1C, 60% of the animals preferred the
water-washed shells as compared to only 15% on the alcohol washed.
Although A. asmi is rarely found on Tequla funebralis shells
inhabited by Paqurus spp., the limpets do not discriminate between
these two types of shells. Thus, using the usual test system.
Lani Alleman
equal numbers of limpets were found on sealed T. funebralis shells
containing Paqurus spp. as on Parowax-sealed T. funebralis shells
containing its normal host (Fig. 10). Similar to normal shells,
the attraction of Paqurus-inhabitated shells is lost when treated
with alcohol (Fig. 1E).
A final preference test series was made with old uninhabited
Tequla shells found on the beach. Fig. Ir shows that Acmaea asmi
prefers normal inhabited shells to these old shells. However, as
shown in Fig. 16, treatment of normal shells with alcohol renders
them as unattractive as the old shells.
The above experiments suggest that the "attractant" is com-
pletely removed or destroyed by alcohol, and partially removed or
destroyed by distilled water. Furthermore, it is found on requla
shells inhabited by either T. funebralis or Pagurug spp., but is
not found on uninhabited shells found on the beach. The "attractant"
then, could be an alga or bacterial film associated with the shell,
ch is removed or destroyed by alcohol or distilled water.
However, the major algal epiphyte found on T. funebralis is also
found on the shells of Tequla brunnea and Acathina spirata (Eikenberry
and Wickizer, 1964), which are not the normal hosts for Acmaea asmi
Behavioral observations.
The above results on preference are consistent with a diffus
ible "attractant" emanating from the Tequla shell. Behavioral
observations, however, indicate that the preference might be made
at the tactile rather than olfactory or chemosensory level.
Continuous observations were made of the selection process in
Lani Alleman
a test situation where normal, sealed Tequla funebralis shells were
alternated with alcohol-treated ones.
As soon as the Acmaea asmi were placed in the center of the
Tequla funebralis circle, they extended their tentacles and began
to feel the substrate. These tentacles are thin and almost as long
as the shell when fully extended. They are moved in a tapping man-
ner from side to side as the animal crawls in a seemingly random
fashion across the bowl. When a specimen touched another A. asmi
with its tentacles, it felt the shell and then climbed immediately
onto it.
If a limpet crawled between two Tequla funebralis shells, one
alcohol-treated and the other not, it would tap each shell with its
tentacles and then, in every case observed (11), climb onto the un¬
treated shell. If, however, the A. asmi encountered only one shell,
whether alcohol-treated or not, it would generally climb on. Once
on a shell, the A. asmi continued to move and sometimes changed
shells. Out of twenty-five animals tested, nine were at one time
or another on alcohol-treated shells. After eight hours, when the
experiment was concluded, only two limpets were still on these shells.
From these latter observations, it seems that Acmaea asmi is not
reacting to some diffusible chemical attractant from the shell, but
rather testing the substrates with its tentacles. It will crawl on
the first curved surface encountered, but if other choices are
available, will eventually end up on the preferred substrate. It
is interesting to note that Test stated that the diffusible attrac-
tant was sensed at seven mm and Radford felt the range to be ten mm.
If an A. asmi is placed this close to a T. funebralig, it can generally
Lani Alleman
touch it with its tentacles and would, therefore, react to its
presence
SUN
The behavioral basis of the association between Acmaea asmi
and Tequla funebralis has been investigated. The observations
indicate that A. asmi is not attracted by a diffusible substance,
but senses its substrate through contact with its tentacles. The
critical substance(s) on the shell are easily destroyed or dis-
solved by ethanol and slightly removed by distilled water.
These factors are also present on Paqurus-inhabited Tequla
shells, but are not found on uninhabited shells found on the beach.
Lani alleman
ACKIOMLEDGENENTS
This work was made possible by Grant G1806 from the Undergraduate
Research Participation Program of the National Science Foundation.
I also wish to thank Dr. David Epel, Dr. Donald P. Abbott, and
Mr. Roger Kingston for offering helpful advice.
20
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Lani Alleman
LITERATURE CITED
Eikenberry, Arthur B., Jr., and Diane E. Wickizer
1964. Studies on the Commensal Limpet Acmaea asmi in Relatien
to its Host, Tegula funebralig. The Voliger 6 (Suppl.): 66-70.
Radford, Ruth
1959. A Study on Aomaes asmi. Unpubl. Stanford University
honers paper.
Test, Frederick
1945. Substrate and Mevements of the Marine Castroped Acmaes
asmi. Amer. Midland Naturalist 33: 791-793
2
FOOTNOTES
Footnote 1, page 1-Permanent address:
Lani L. Alleman
Lani Alleman
Preference of A. asmi to various substrates. Twenty.
Figure I.
five A. asmi were tested in each experiment. Each test
(A-H) represents the percentage of animals found on the
indicated substrate (percentages of those not responding
are not shown).
C
O
onror (70%)
.
AlCONOA-TREATEO (10%)
oNTot (65%)
WATER-TREATEO (25%)
Acotol-TREATEO (15%
MATEE-TREATED (60%)
Pas( T ses 18%
TEGUA AN TEGOA SHE 30%
Paeuels -eonreo (48%)
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