J. comp. Physiol. 126, 293-295 (1978)
Journal
of Comparative
Physiology. A
9 by Springer-Verlag 1978The Influence of Substrate Contact on Gravity Orientation
Substrate Orientation in Spiny Lobsters V
H e r m a n n Sch6ne, D o u g l a s M. Neff*, and Felicita Scapini**
Max-Planck-Institut ffir Verhaltensphysiologie, D-8131 Seewiesen, Federal Republic of Germany Accepted May 31, 1978
Summary. Tilting o f the a n i m a l with respect to gravity results in c o m p e n s a t o r y eyestalk m o v e m e n t s a n d in leg c o u n t e r f o r c e reactions which v a r y with the n u m b e r a n d sequential position o f legs t o u c h i n g the b o d y - f i x e d substrate b o a r d (Figs. 2, 3). T h e gravity response is reduced with increasing n u m b e r o f legs t o u c h i n g the substrate. The results fit an interpreta- tion that the weight o f the substrate input interacting with gravity signals results f r o m superposition o f the weighted effects o f the single legs involved (Figs. 2,
4).
Introduction
Spiny lobsters, as m a n y Crustacea, live in a r o c k y habitat, they walk a n d climb on inclined or vertical surfaces a n d hide in crevices where they sometimes cling to the vertical walls. Therefore the substrate is a very i m p o r t a n t reference. Its i m p o r t a n c e , h o w - ever, is reduced, if the a n i m a l loses c o n t a c t with the wall a n d is s u s p e n d e d free in the water. T h e n it relies u p o n the gravity input. This p a p e r contributes to the u n d e r s t a n d i n g o f the m e c h a n i s m o f interaction o f the two i n p u t systems involved.
G r a v i t y input is m e d i a t e d by the statocysts, sub- strate input by p r o p r i o c e p t o r s in the basal joints o f the legs (Sch6ne et al., 1976) a n d o t h e r leg receptors r e s p o n d i n g to changes in the geometrical l e g - t o - b o d y relation (Scapini et al., 1978). It has been s h o w n that the gravity input interacts with the substrate i n p u t ; * Permanent address: Department of Zoology, University of Glasgow, Scotland
** Permanent address: Istituto di Zoologia, UniversitA di Firenze, Italy
n o r m a l l y b o t h signals are taken into account. W h e n the substrate is tilted against the a n i m a l the c o m p e n - s a t o r y eyestalk response is larger in animals with no statoliths t h a n in animals with n o r m a l f u n c t i o n i n g statocysts (crayfish: Stein a n d Sch6ne, 1972; spiny lobster: Sch6ne a n d Neil, 1977). O t h e r results s h o w that the s u b s t r a t e - m o d u l a t e d eye response is different at different b o d y positions to gravity, indicating that the " w e i g h t " o f the gravity input is variable (Stein a n d Sch6ne, 1972), A n o t h e r a r r a n g e m e n t o f the two inputs was investigated here: Substrate position was c o n s t a n t with respect to a n i m a l (with different n u m b e r s of legs m a k i n g contact), a n d gravity input was m o d u l a t e d . The reactions m o n i t o r e d were c o m - p e n s a t o r y eyestalk m o v e m e n t a n d leg counterforce.
Materials and Methods
The experimental animals (Palinurus vulgaris) were imported from the Thyrrenian coast of Italy and maintained under semi-natural conditions in the lab.
Apparatus and general procedure have been described before (Sch6ne et al., 1976; Neil and Sch6ne, 1978). The animal was fixed with its dorsal side to a holding device, which was combined with a footboard. The framework could be tilted with respect to gravity (Fig. 1). Position was recorded by means ofa potentiome- ter, eye movement by a miniature angle transducer (Marrelli and Hsiao, 1976), force by a strain gauge (Grass FT 0.3 ~ all signals being continuously recorded on a chart recorder (Philips oscillo- script).
The board was fixed in relation to the body. The legs could be lifted off the board by strings fastened to the framework. Body plus board were oscillated from 0 ~ to 30 ~ left side down tilt about an axis running along the midline of the board.
Thus the main point of the procedure is to tilt the animal together with its substrate reference against gravity.
Data points were derived from the original records by averag- ing of 6 to 10 cycles, the variability of response amplitude being small.
294 H. Sch6ne et al. : Gravity Orientation in Spiny Lobsters
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Fig. 1. Setup for recording eyestalk responses and force responses of spiny lobsters when tilted against gravity with body-fixed sub- strate board. The animal is shown in a stylised front view with eyestalks and legs
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Fig. 2a and b. Eyestalk reaction to statocyst and substrate input. Oscillatory movement of animal plus board against gravity (0-30 ~ left) with (a) increasing number of legs on board, (b) single pairs of legs on board. The line in a was calculated thus: taking into account a "weighting factors" (cf. text). The upper inset figure refers to a stylised frontview of the animal with some legs lifted from board, the left inset figure demonstrates a dorsal view with legs numbered
H. Sch6ne et al. : Gravity Orientation in Spiny Lobsters 295 Results
Eye a m p l i t u d e with no legs on the b o a r d represents the c o m p e n s a t o r y response to statocyst input. The eye response reduces as successively m o r e legs c o n t a c t the board. W h e n all legs are d o w n the response is r e d u c e d to 30% o f initial a m p l i t u d e (Fig. 2a).
Individual leg pairs were tested separately a n d re- sults indicate that their m o d u l a t i o n o f statocyst re- sponse differs with leg n u m b e r , the greatest effect being p r o d u c e d by legs 3 (Fig. 2b).
D u r i n g b o d y tilt the force i m p a r t e d by all the legs o n t o the b o a r d is less than 10 g (Fig. 3). As the n u m b e r o f legs on the b o a r d is reduced the force p r o d u c e d in response to b o d y tilt increases in p r o p o r - tionality with increase in eyestalk m o v e m e n t .
T h u s the leg c o n t a c t is " w e i g h t e d " in its interfer- ence with the gravity input. This holds true f o r the c o m p e n s a t o r y eyestalk m o v e m e n t s a n d f o r the coun- terforce ( = r i g h t i n g reaction) o f the legs.
D i s c u s s i o n
The results o f the force m e a s u r e m e n t s a p p e a r to be a p a r a d o x : The righting force exerted o n t o the b o a r d d u r i n g b o d y tilt is smallest when all legs t o u c h the b o a r d , a n d increases as the n u m b e r o f c o n t a c t i n g legs is r e d u c e d (Fig, 3). M o r e legs s h o u l d be capable o f p r o d u c i n g larger forces, b u t in fact p r o d u c e smaller.
This c o n t r a s t s to the finding t h a t s t r o n g forces are p r o d u c e d by the animal, when either the substrate is tilted with respect to a n i m a l or when the animal is tilted with respect to substrate plus gravity (Sch6ne a n d Neil, 1977; Neil et al., 1978), Forces up to 500 g have been measured,
T h e p a r a d o x is resolved if we analyse the eye re- sponse which is also reduced in m a g n i t u d e if the n u m b e r o f b o a r d - t o u c h i n g legs increases. T h a t is in b o t h cases the effect o f the substrate input in reducing the gravity signal increases as the c o n t a c t o f the ani- mal with the substrate gets larger. We see differences in the c o n t r i b u t i o n o f the individual leg pairs to this effect (Fig. 2b). A c o m p a r i s o n can be m a d e with the results o f o t h e r experiments, where the leg move- m e n t released the eye response (Fig. 4). In each case the influence o f a leg is o f the same relative magni- tude, leg 3 exerting a large influence. T h e c o m - bined effect o f several legs is explained if we assume t h a t in the neural c o m p u t a t i o n " w e i g h t i n g f a c t o r s " f o r each leg are i n c o r p o r a t e d , the values o f which can be derived f r o m Figure 4.
The sum effect o f each leg c o m b i n a t i o n can be
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calculated f r o m addition o f the effects o f individual leg pairs weighted a c c o r d i n g to the results o f Figure 2b, as replotted in Figure 4. The result o f such a calculation is represented by the line in Figure 2a. It indicates that the weight o f the substrate input interacting with the gravity signals results f r o m super- position o f weighted effects the single legs involved. Acknowledgements are due to the Max-Planck-Institut (D.M. Neil, F. Scapini) and to the Carnegie Trust (D.M. Neff) for financial support. We want to thank Renate Alton for her co-operative help.
R e f e r e n c e s
Marrelli, J.D, Hsiao, H.S. : Miniature angle transducer for marine arthropods. Comp. Biochem. Physiol. 54 A, 121 123 (1976) Neil, D.M., Scapini, F., Sch6ne, H. : Leg resistance reaction as an output and an input (Substrate orientation of spiny lobsters V1). Submitted for publication (1978)
Neff, D.M., Sch6ne, H.: Input-output analysis of eyestalk re- sponses (Reactions of the spiny lobster, Palinurus vulgaris to substrate tilt II). J. exp. Biol, (in press)
Scapini, F., Neil, D.M., Sch6ne, H. : Leg-to-body geometry deter- mines eyestalk reactions to substrate tilt (Substrate orientation in spiny lobsters IV). J. comp. Physiol. 126, 287 291 (1978) Sch6ne, H., Neil, D.M. : The integration of leg position-receptors
and their interaction with statocyst inputs in spiny lobsters (Reactions of Palinurus vulgaris to substrate tilt III). Mar. Be- hay. Physiol. 5, 45-59 (1977)
Sch6ne, H., Neil, D.M., Stein, A., Carlstead, M.K.: Reactions of the spiny lobster, Palinurus vulgaris, to substrate tilt (I.). J. comp. Physiol. 107, 113-128 (1976)
Stein, A., Sch6ne, H. : Ober das Zusammenspiel yon Schwereorien- tierung und Orientierung zur Unterlage beina FluBkrebs. Verb. Dtsch. Zool. Ges. 15, 225-229 (1972)
