A BEHAVTORAL INVESTIGATTON INTO THE FUNCTIONS OF THE FIRST
AND SECOND ANTENNAE OF PAGURUS GRANOSIMANUS (STIMPSON,
1859), AND PAGURUS SAMUELIS (STIMPSON, 1859 ).
SALLY K. ROLLEFSON
Hopkins Marine Station of Stanford University
Pacifio Grove, California
Running Head:
Functions of Pagurus Antennae
Introduction
The very prominent and active first and second antennae of
the various species of Pagurus, make them an obvious subject for
a functional behavioral study. The lack of literature and the
many contradictions in what literature there is on the subject,
also encourages such a study. This paper will attempt to explore
some of the possibilities of such a problem; particularly with
respect to chemoreception, rheotaxis, and taotile reception.
Studies were made at Hopkins Marine Station, Pacifio Grove,
California, during April and May of 1965. Two species of
Pagurus, P. Samuelis and P. granosimanus, were used. Both
species are common in the intertidal regions around China Point,
Monterey Bay, with P. granosimanus found slightly lower insthe
intertidal where it is subjected to stronger currents than P.
samuelis.
Methods
The primary method employed was direct observation of intact
crabs, both in the field and in the laboratory, and later of
crabs subjected to various extirpations of antennae and other
appendages. Operations were performed on unanesthetized crabs
which had been poked out of their shells with a probe, after a
hole had been hammered in the side of the shell. Crabs were
allowed to return to their shells immediately after the operations,
which were performed with a pair of fine scissors. Antennules
were removed down to the first articulation next to the statocyst,
and in one group the statocysts were also removed. Removal of the
statocysts did not appear to hamper a crab particularly, but
such crabs were very slow to return to their shells.
In attempts to demonstrate chemoreception, a technique sim-
ilar to that described by Barber (1961 ) was used. Blotters
were impregnated with the various test solutions and added to a
basin containing the crabs to be tested. Food, such as fresh-
crushed Mytilus edulis or Tegula funebralis, was also added to
tidepools and tanks, and observations made.
To examine left-right tendencies å "Y" of rocks was set up
in a tank and orabs were individually tested for possible
directional preferences. To avoid light effects, these tests were
performed indoors and the tank was turned around after each trial
and the orab tested again. Each crab was tested at least twice.
For the rheotactio studies, a procedure similar to that
used by Luther (1930) was followed. A glass dish approximately
15 centimeters in diameter was anchored in the center of a larger
glass dish approximately 30 centimeters in diameter, to provide
a convenient channel in which currents could be easily produced and
reversed with a direoted stream of water. Each crab was tested
four to five times in succession by means of reversing the eurrent
when a response was elicited. When the crab did not respond to
the current change after two revolutions about the dish, the
current was reversed and the lack of response recorded. The
normal response of both P. granosimanus and P. samuelis to a
current is to move into it, at first facing the current, then,
as the strength of the current increases, turning sideways, and
finally, backing into the current in short hops. When the crab
can no longer move against the current, he relaxes and is carried
to a point where he can again move against it. In this paper,
such behavior is considered a positive rheotactic response.
Results
Crabs lacking antennae appear able to lead close to normal
lives, and recover quickly from the operation. Mortality was
not noticeably heightened in the operated crabs and most survived
at least five weeks in the laboratory. Operated crabs did show
an increase in aggressive behavior toward other crabs, however,
and were slow in returning to their shells after operation. There
was no appreciable differenoe in the dispersal times of operated
and intact crabs, but operated crabs exhibited less exploratory
behavior than intact crabs. Crabs without second antennae were
especially non-exploratory.
It was generålly observed that the second antennae are closely
to visual activity, being stimulated by sight into an exploratory
and tactile response. The antennae are quickly withdrawn on contaot
with objects, and are seen to follow objects passed in front of the
orab, even from the other side of a glass partition. Blinded
crabs dod not exhibit such a following response, although they do
avoid objects and other crabs. Grabs which were blinded and
without either pair of antennae also avoided objects in their paths
without any apparent bodily contact, however, which would
indicate a complex sensory system involving more than just the eyes
and antennae. The second antennae have also been observed
snagging escaping food partioles. Crabs without second antennae
showed a slight tendency to extend their walking legs wider and
further in front of them than unoperated crabs.
No evidence for chemotaxis in the two species of Pagurus was
found. Even intaot orabs do not exhibit a directed response,
either to food, in the form of mussel or snail meat, or to such
chemicals as acetic acid, beta alanine, quinine, dextrose, maltose,
sucrose, or lactose. In no case was andescape response to a
predator found. Blinded crabs showed no response to food dropped
directly in front of them.
There was no apparent left or right preference, either in
intact crabs of crabs without one or both first and second antennae.
The number of crabs tested ranged from 25 to 35 per group, with
a total of 442 orabs tested in all.
Figure 1 shows the results of the rheotactic tests. Positive
rheotactio response is virtually eliminated in P. granosimanus
lacking either all of the first antennae, or the brushes of the first
antennae. Extirpation of only the right or left first antenna
also showeddå lowered number of positive responses; out of twenty
trials five crabs gave a positive response only 60 per cent of
the time without the right antennule, and without the left
antennule the same number gave 65 per cent positive responses.
Extirpation of the second antennae or of the maxillipeds had
no effect. P. samuelis, on the other hand, shows no such loss of
rheotaxis with removal of the first antennae. The P. samuelis
o
n210
T=50
2
2 80
60
867
40
20
INTACI
P SAMUELIS
n230
1o0
TEIIO
80
94%
2
60
40
20
TACT
n210
T250
84
NO
ANT.
n210
T-90
86
NO
ANT,
NO
ANT
n220
T200
92
n230
TE 146
27
NO
ANT
n=20
T2100
35
BRUSHES
ANT
n210
1=50
96
NO
MXPD
n220
T2100
87
NO
MXPD
FIG. I
crabs were much slower to respond to the current when a response
was observed, however, than were the P. granosimanus. A total of
110 crabs were tested, and within each group there was a
remarkable consistency of response. It was also noted that both
species of Pagurus continually align their antennules into currents,
even when backing into them. Brock (1930 ) found similar
behavior in Carcinus maenas.
Discussion
In studies on chemoreception in other decapods, Hodgson ( 1958),
and Case and Gwilliam ( 1961 ) found little evidence for
chemoreception by either pair of antennae, but did find very
sensitive receptors on the dactyls of the walking legs. In the
present study, no evidence for a directing chemoreceptive organ
was found, but in tests with glaeial acetic acid it was noted
that the dactyls and mouth parts were apparently more sensitive
than other parts of the crab. The fine brush structure of the
antennules and their orientation with currents would make them
a logical chemoreceptive organ, but no indication of such a function
was found in this study.
The most interesting results were those on rheotaxis. It
was a surprise to find that two animals of the same genus, living
at times in the same tidepool, should display such a difference
in rheotactic behavior. Luther (1963 ) found similar differences
between certain decapod genera, though. P. granosimanus is found
in areas of stronger current than is P. samuelis,which may help
to explain the difference. P. granosimanus, because of its
greater exposure, may have lost all current sensitivity except
in the antennules. P. samuelis may have body hairs which are
current sensitive, or it may simply react to pressures on its
shell. A neurophysiological investigation is the next logical
step.
Summary
lons of the first and second
A behavioral study of th
antennae of Pagurus granosimanus and Pagurus samuelis was made.
The primary method was extirpation and comparison with intact
crabs. No chemotazis or lefteright preference was observed.
Rheotaxis was found to occur in both species, but antennular
involvement was only evident in Pagurus samuelis.
Literature Cited
Barber, S., (in Waterman, T. Ed. (1961
Physiology of Crustacea II: 112-113
Academic Press, N. Y. (681 p%2 )
(1930
Brock, F.
Das Verhalten Der Ersten Antennen von Brachyuren und Anomuran
in Bezug auf das Umgebende Medium
Verg. Phys. 11: 774-790
Case, J., and G. F. Gwilliam (1961
Amino Acid Sensitivity of the Dactyl Chemoreceptors of Carcinides
maenas
121: 449-455
BIOI. Bull.
1958
Hodgson, Edward
Electrophysiological Studies of Arthropod Chemoreception
Biol. Bull.
115: 114-125
1930
Luther, W.
Versuche über die Chemorezeption der Brachyuren
12: 177-206
Verg. Phys.
Luther, W. „( 1963 )
Versuche über die Funktion der 1. Antenne von dekapoden Krebsen
als Strömungssinnesorgan
Helgolander Wiss. Meeresuntersuchungen
844): 321-332
Legend for Fig. 1.
Percentage of positive rheotactic responses observed in A)
granosimanus. (n- total number
P. samuelis, and B) P.
crabs tested per group;
Te total number of trials per grou