CARACTERISTICAS TECNICAS Y DE LOS

The u t i l i z a t i o n o f a number o f fe e d in g methods in o p h iu ro id s re q u ire s th a t th e a n im a ls possess an e ff e c t iv e chemosensory a b i l i t y . (F o r re vie w o f o p h iu ro id fe e d in g methods see W arner 1 9 8 2 ). O phiura lip h i.u rA i s known to o b ta in n u tr ie n ts frcm suspension fe e d in g (S tubbs and Cobb . 1982) and scavenging, ( Nagabushanan and Colman 1959) and p re d a tio n . P e rip h e ra l c e llu la r tis s u e s th a t a re e x te rn a l may be v a r ia b ly dependant on th e d ir e c t uptake o f amino a c id s fro m th e s u rro u n d in g seaw ater (see Ferguson 1982 f o r re v ie w ) .

Amino a c id s have been shewn to be e f f e c t iv e chemosensory s tim u li i n fis h ,( C a r p io 1978) c ru s ta c e a n s , (C a rr 1978) and more r e c e n tly to i n i t i a t e a p p e titiv e b e h a v io u r i n a number o f echinoderm s (d e s c rib e d b e lo w ). 0 .o p h iu ra d e te c te d a l l te n amino a c id s and B e ta in e and in a l l cases th e amino a c id s e lic it e d b e h a v io u ra l responses i n th e a n im a ls in th e form o f th e arm c o ilin g response a t c e r t a in c o n c e n tra tio n s . C o llin s (1974, 1975) in d ic a te d t h a t L - P r o lin e from c o ra ls was re s p o n s ib le f o r a b o ra l arm c o ilin g i n th e c ro w n -o f-th o rn s s t a r f is h A c a n th a s te r p la n c i and Moore and H uxley (1976), showed t h a t a fe e d in g response i n th e same a n im a l c o u ld be e l i c i t e d -b y s in g le amino a c id s . A ra k i (1965) dem onstrated t h a t stomach e v e rs io n i n P a tir a m in ia ta was in d u ce d by in d iv id u a l amino a c id s and Z a f ir io u (1972)

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showed s in g le amino a c id s were w eakly a tt r a c t iv e to A s te ria s v u lg a r is . V a le n tin c ic (1975,1978) w o rk in g w ith M a rth a s te ria s a la c la l is dem onstrated t h a t th e amino a c id s L -C y s te in e h y d ro c h lo rid e and L - P r o lin e were most s tim u la to ry in fe e d in g and L -C y s te in e e li c i t e d se a rch in g b e h a vio u r o r th e a p p e titiv e phase o f th e fe e d in g re sp on se . Only C a s t illa (1972) has re p o rte d th a t both in d iv id u a l and m ix tu re s o f amino a c id s have proved " r e p e lle n t” to th e b e h a v io u ra l anim al A s te ria s rubens. I t i s d i f f i c u l t to u n d e rsta n d why t h i s sh ou ld have occured in th e l i g h t o f a l l th e o th e r w o rk where amino a c id s have appeared a t t r a c t iv e to a number o f o th e r a s te ro id s .

The neurones re c o rd e d fro m in t h i s stu d y are alm ost c e r ta in ly a c la s s o f in te rn e u ro n e s and n o t th e sensory

neurones th e m se lve s. The chem oreceptors i n

O phiura o p h iu ra are not lo c a te d i n s p e c ia liz e d organs and a re presumed to be d is t r ib u t e d g e n e ra lly o ve r th e sp in es and tu b e fe e t. The minimum th re s h o ld c o n c e n tra tio n s re co rd e d i n t h i s study may th e re fo re n ot be th e a b s o lu te th re s h o ld s and i t i s p o s s ib le th a t th e th re s h o ld s f o r each sensory neurone a re lo w e r th a n th o se measured when re c o rd in g frcm la rg e in te rn e u ro n e s . E x c ita tio n o f the in te r n e urones may w e ll be a fu n c tio n o f th e o v e r a ll in p u t fro m th e sensory re c e p to rs * I t must a ls o be remembered t h a t th e b e h a vio u r s tu d ie s w ere p erfo rm ed on whole a n im a ls and n o t s in g le arm p re p a ra tio n s as in th e e le c tr o p h y s io l o g i c a l e x p e rim e n ts . The in c re a s e d number o f re c e p to rs a v a ila b le on th e w hole a n im a l compared to a

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s in g le arm, may be c r i t i c a l in p ro v id in g th e needed e x c it a t io n to produce an in te rn e u ro n e s p ik e , and i n i t i a t e b e h a vio u r i n th e w hole a n im a l. (The amino a c id s L -P ro lin e and L -S e r i ne were d e te c te d b e h a v io u r a lly a t a

lo w e r c o n c e n tra tio n th a n when re c o rd in g

e le c tr o p h y s io l o g i c a lly , le n d in g w e ig h t to th e th e o ry th a t even lo w e r c o n c e n tra tio n s a re b e in g p e rc e iv e d a t th e re c e p to r l e v e l ) . A t p re s e n t th e tra n s d u c tio n mechanism i n echinoderm chem oreception i s n ot u n d e rstoo d .

The th re s h o ld s o f d e te c tio n f o r each amino a c id and B e ta in e were c o n s is te n t between p re p a ra tio n s when re c o rd in g e le c tr o p h y s io lo g ic a lly . The th re s h o ld s o f b e h a v io u ra l response i n th e ta n k e xp e rim e n ts however v a rie d between in d iv id u a l a n im a ls and w ith th e e xce p tio n o f L -S e ri ne and L - P r o lin e , were alw ays a t a much h ig h e r c o n c e n tra tio n . In g e n e ra l th e arm c o ilin g b e h a vio u r was most p re v a le n t a t th e h ig h e r c o n c e n tra tio n s . Lower c o n c e n tra tio n s e lic it e d o n ly a movement tow ards th e s tim u lu s , su g g e stin g th a t d if f e r e n t b e h a v io u r i n th e a n im a ls i s e lic it e d a t d if f e r e n t c o n c e n tra tio n s . Reimer and Reimer (1975) w o rk in g on fo u r sp e c ie s o f o p h iu ro id s o f th e genus Qphioderm a a ls o showed t h a t d if fe r e n t c o n c e n tra tio n s o f c e r ta in amino a c id s produced d if fe r e n t b e h a v io u ra l responses. A ga in L - P ro lin e e lic it e d fe e d in g b e h a v io u r, b u t th e arm c o ilin g response was co n sid e re d by Reimer and Reimer to re q u ir e b oth a chem ical and m echanical s tim u lu s . T h is was n o t th e case i n Q. o p h iu ra , where arm c o ilin g was in d u ce d o n ly by th e presence o f L - P ro lin e i n th e w a te r column and n o t by th e a d d itio n o f

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mecdianical s tim u la tio n o f th e tu b e -fe e t as w e ll.

Amino a c id s p re se n t in th e w a te r column may s ig n a l a fo o d source i f d e te c ta b le c o n c e n tra tio n s o f these compounds a re re le a s e d by th e n a tu ra l foods o f 0 . o p h iu ra . In g e n e ra l c a rn iv o re s and scavengers respond t o commonly o c c u rrin g amino a c id s em anating fro m prey tis s u e . The p ro te in s o f many m arine in v e rte b ra te s c o n ta in h ig h le v e ls o f th e amino a c id s L - P r o lin e , L -A la n in e , L -V a lin e , L -L e u c in e , and L -S e rin e . (V egotsky and Fox 1962). In a d d itio n many m arine in v e r te b r a te s may e x c re te as much as 20-30% o f t o t a l n itro g e n in d ig e s te d i n th e form o f unchanged amino a c id s (B a ld w in 1963).

P o lych a e te s commonly encountered i n th e h a b ita t o f 0. ODhiura have been shown by Delauney (1913) and F ontes and Thouveny (1972) to c o n c e n tra te fre e amino a c id s such as L -P r o lin e , L -A la n in e , L -L e u cin e and L -S e rin e e x t r a c e llu la r ly . The a p p e titiv e b e h a vio u r e lic it e d by these amino a c id s i n th e b r it t le s t a r s su g g e sts th a t these ch e m ica ls may s ig n a l th e presence o f a f a m ilia r prey ite m i n th e e n viro n m e n t.

D ista n ce chem oreception p ro v id e s in fo r m a tio n n ot o n ly c o n ce rn in g p re y r e c o g n itio n b u t a ls o th e id e n t if ic a t io n o f p re d a to rs . The s iz e o f th e p re d a to r and th e th r e a t i t may p re se n t to these b r i t t l e s t a r s may be s ig n a lle d n o t o n ly by c e r ta in compounds em anating fro m th e in d iv id u a l p re d a to rs , b u t a ls o by th e r e la t iv e amounts re le a s e d by th e p re d a to r. C e ssa tio n o f a c t i v it y a t th e o n se t o f p re d a to r re c o g n itio n may p re ve n t

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d e te c tio n . However, t h i s b e h a vio u r i s o v e rrid d e n t a c t i l e s tim u la tio n from th e p re d a to r r e s u lt in g in th e recommencement o f m otor a c t i v it y and th e ra p id movonent away o f th e b r i t t l e s t a r as d e s rib e d on page 4 0. T h is p ro v id e s f u r t h e r evidence f o r a h ie ra rc h y o f response p re s e n t w it h in th e b r i t t l e s t a r s dependant upon typ e and le v e l o f s tim u lu s in p u t.

The d if f e r e n t phases i n th e sequence o f response f o llo w in g d e te c tio n o f a fo o d ite m have been v a rio u s ly d e s c rib e d i n o th e r o p h iu ro id s p e c ie s . Hyman (1955) d e s c rib e d th e w aving movements o f th e arms i n c a rn iv e ro u s