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NELSON, M .E . and L.D. MECH, 1981. - De~ r social organization and wolf predation in north eastern Minnesota . Wild/. Monogr., 77 : 1-53 .

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PACKER, C . , 1986. -The ecology of socialit y 111 felids . In : D. I. Rubenstein and R .W . Wrangham, eds . Ecological aspects of social evaluation, pp . 429-451. Princeton : Princeton Univ . Press .

PATEL, A . (in press). -Are chital stags more vu lnerable to dhole predation? J. Bombay Nat . Hist. Soc.

PtMLOTT, D., J . SHANNON and G .B. KOLENOSKY, 1969. - The ecology of timber wolf in Algonquin Provincial Park . Dept. La nds and Forests, Ontario .

RABtNOWtTZ, A ., 1989. - The density and b<'11aviour of large cats in a dry tropical forest mosaic in Huai Kha Khaeng wilct ,ife sanctuary, Thailand. Nar. His!. Bull. Siam Soc., 37 : 235-25 1.

RAVt CH EL LAM (in prep.); Ecology of Asiatic lion (Panthera Ieo persica). Ph . D. Thesis, Saurashtra Univ ., Rajkot , India.

SCHALLER, G . B. , 1967. - The deer and the rig..:r : a study of wildlife in India. Chicago: Univ . Chicago Press.

SCHALLER, G. B., 1972. - The Serengeti lion : a study of predator-prey relations. Chi­cago : Univ. Chicago Press.

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Biotropica, 8 : 225-234 . · SUNQUtST, M.E. , 1981. - The social organi zat ion of tigers (Pantlrera tigris) in Royal

Chitawan National Park, Nepal. Sm ir hsonian Contrib. Zoo/., 336 : 1-98 .

SuNQUtST , M. E. and F.C. SUNQUtST, 1989. - Ecological constraints on predation by large felids. In : J .L. Gittleman, ed . Carnivore behaviour, ecology and evolution, pp. 283-301. Chapman and Hall Ltd . , London .

TAYLOR, R.J . , 1976. - Value of clumping to prey and the evolutionary response of ambush predators . A mer. Nat ., 11 0 : 13-29.

~

Behavioral evidence against possible subaquatic electrosensitlvity in the pyrenean Desman Galemys pyrenaicus (Talpidae, Mammalia).

by P.A. SCHLEGEL 1 and P .B. RICHARD 2

'Zoologisches lnstitut, LMU, Luisenstr. 14, D 8000 Miinchen 2, Germany

1 Laboratoire Souterrain CNRS Moulis F 09200 Sr-Girons, France

Summary. - The poss ibility of electrosensitivity of the Desman in immersion is tested by the method of conditioning : neither spontaneous nor obvious responses linked to the stimuli (overt responses) was noticed . The unique animal kept in captivity was tested in the experimental tank . Single or repetitive (sine or square) st imuli were applied thro ugh 2 silver wire electrodes . lntensities, possible in a natural environment, in the range of 10 m V / cm, remained without response. Stimuli of much higher magnitude (3 - IOV between the electrodes) which can be considered as giving a << mild )) electroshock provoked a sli ght retraction of the trunk. These shocks were felt , on the tongue of the experimenter, as galvanic electricity . The Desman therefore showed a sensibility close to that of man . From these results we can suggest, as an hypothesis, that the electrical sense is rather improbable with Mammals <<sensu stricto )). This is the case of the Desman which can be considered as an animal well adapted to subaquatic life , although not living under selective pressure in its narrow ecological << niche )) : it does not show any significa ti ve respo nse to electrical acti vities of biological origin (electrom yograms) . It distin­guishes itself from the Platypus (Monotremata , Prototheria), which lives in a similar enviro nment and shares the same diet as the Desman : it possesses an evident electrosensiti ­vi ty. Formerly adapted to a new habitat it has apparently developed an electrical sense secondarily, which lower aquatic Vertebrates have originally always possessed and used for orientation in electrical field to detect and catch preys .

Resume. - La possibil ite d ' une electrosensibilite chez le Desman en immersion est testce par la methode de conditionnement : aucune reponse sponta nee, ni aucune reponse clairement lice a des st imuli n'a pu et re mise en evidence chez un unique animal garde en captivitc dans un aquarium oil o n l'a soumis a des stimuli electriques isolcs ou repetitifs , periodiques ou continus, delivres entre 2 fils d'argent. Des intensites vois ines de 10 m V /cm n · ont don ne aucune reponse. Des sti muli beau coup plus eleves (3 -1 OV entre electrodes), qu 'o n peut deja consiuerer comme donnant un choc electrique fai blc, provoqua ient une lcgerc retraction de I~ i1ompe. Ces chocs etaicnt rcssenti s. sur la la nguc de l'ex perimentateur

Momm., 'm. I 51\. 11 ° 4. 1991

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528 MAM MALI A

comme des courants galvaniques. Le Desman n10ntre done une scnsibilite proche de celle de l'homme. De ces resultats on peut conclu rc, a titre d'hypothcsc, qu ' un sens electrique est peu probable chez les Mammiferes placcn taires. C'est le cas du Desman qu 'on peut considerer comme bien adapte a la vie subaquatique, bien qu'il n'ait pas ete soumis, dans sa niche ecologique etroite, a une fo rte pression selective : il ne montre pas de reponse significative aux activites manifestemcnt elcctriques d'origine biologique (electromyo­grammes). Cela le distingue a !'evidence de Platypus (Monotremata, Prototheria), qui vit dans un environnement et un regime ali mentaire semblables a ceux du Desman: le premier possede une electrosensitivite evidente. Arrive dans un habitat nouveau, il a dO developper secondairement un sens electriquc que les Vertebrcs inferieurs aquatiques ont possede depuis les origines et qui leur sert a s'orienter dans le champ electrique, et a detecter les proies .

INTRODUCTION

Electrosensilivity in lower vertebrates. - The electrical sense is very common among the lower aquatic vertebrates (llu ll ock 1974; Bullock and Heiligenberg 1986). Besides the highly evolved active clectrosensory system in weakly and strongly electrical bony fishes (Fessard and Szabo 1974), some other families of bony fishes and all elasmobranchs (M urray 1962) possess passive electrosensiti­vity mediated through their ampullary o rgans ( = pit organs; Roth 1969, 1973). They are also characteristic for most amphibian classes, e.g. gymnophiones (Fritzsch and Miinz 1986) and the larvae of urodeles (Fritzsch and Wahnschaffe 1983) and even in the adults of the neotenic axolotl (Miinz et al. 1984) and the always aquatic and never metamorphosizing proteidae (Proteus anguinus; Roth and Schlegel 1988) but are absent in anurans, even in their tadpoles. After metamorphosis, the amphibians loose the electrical sense , i.e. the electrical organs degenerate (Fritzsch and Wahnschaffe 1983), and only the neotenic axolotl and the Blind Cave Salamander, Proteus, keep the am pullary organs during the whole life time unless metamorphosis is induced by means of the hormone thyroxine (ref. see in: Miinz et al. 1984). Hence, at least these two groups of amphibians (Proteus and axolotl checked so far) keep their electroreceptors and probably also use them for life . The receptors themselves a re fully comparable, morphologically and physiologically, to those of some actinopterygians and the elasmobranches.

Question of electrosensitivity in higha vertebrates (mammals) . - It seemed impossible for a long time to think of an electrical skin sense beyond the amphibian class of the vertebrates when becoming ter res trial and loosing the electrical sense with metamorphosis along with further -:volution. The electrical sense has not been found in reptiles, birds, and mammals that have become aquatic secondarily . Only recently, Scheich et al. (1986) were able to demonstrate an obvious and comparatively well developed electrosensi tivity, using behavioral and electrophy­si.ological methods, in a primitive mam mal, the Australian Platypus (Monotre­mata, Prototheria). The sensory organs, however, .occupy only the very specialized beak (bill) and cannot be homologized with the ancient ampullary organs of fish and amphibians . lt is clear that the rcccptors arc transformed axons of trigeminal neurons protruding in ducts o f <kin glands, as shown in electron micros-

ELECTROSENSITIVITY IN IJESMAN 529

cope studies by Andres and von During (1984) and Andres et al. (1991). They look morphologically similar and, comparing the electrophysiological features are like those of the lower vertebrates, namely they react phasic-tonically to DC-currents as do the analogic organs of urodeles and fishes (Scheich et al. 1986 ; compare with review by Fritzsch and Miinz 1989, and Roth and Schlegel 1988). Likewise, the biological significance of the electrical sense for the animals can be considered as analogous in lower aquatic vertebrates and in Platypus. This highly specialized animal can presumably detect and localize prey by virtue of the electroreceptors sensitive to the muscular potentials generated by a prey. This ability is limited to rather short distances, typical for electrosensory systems, but still enables these animals to catch jumping shrimps for instance (Scheich et al. 1986).

In higher vertebrates, especially in mammals «sensu stricto», excluding the Prototheria, it appeared rather unlikely to find electrosensitivity similar to that of Platypus or lower vertebrates but has not been looked for so far. However, an ecologically «predestined» candidate in this context was the highly specialized, semi-aquatically living, endemic pyrenean Desman (Galemys pyrenaicus, Insecti ­vora, Talpidae) that has lost almost all eyesight and lives nocturnally in streams and rivers of the middle altitude in the Pyrenees and some Spanish sierras . lt preys mainly nocturnally, as an insectivore, on aquatic larvae of insects (Piecop­tera, Trichoptera and Ephemeroptera etc.), on crustaceans, and <<worms» (Richard 1973, 1981, 1982). This animal seemed, so to speak, preadapted to possible electro­sensitivity as the habitat and the ecological conditions are quite similar to those of Platypus. The Desman has organs with receptor cells on its proboscis (Eimer's organ; Bauchot et al. 1973; probably mainly chemo/mechanosensitive) which could possibly also function as electroreceptors. That is why we tried, using similar behavioral techniques as for the Platypus (Scheich et al. 1986), some urodeles (Miinz et al. 1984; Roth and Schlegel 1988), and fishes (Roth 1969, 1972, 1973) to find possible evidence for electrosensitivity in the Desman .

METHODS

A freshly caught male Desman that had already become familiar with the open air aquatic/terrestrial and rather natural habitat cage (Richard 1973) was, after being partly fed with fly larvae (maggots = « asticots »), introduced into an experimental aquarium of 3.5 m length and 35 cm width . The water level was kept at about 21 cm depth. In the center of the aquarium, a perspex platform of 30 by 20 cm slightly above water level served as a resting place and a plastic box as a hiding place for the Desman, from which the animal was diving and swimming regularly through the aquarium in order to explore the new habitat and eventually to take food from the ground. The animal did not show any particular stress, although it was a little bit excited by the situation . The aquarium was equipped with one silver plate elect rode placed onto one small side of it and three silver ball electrodes at the left, the right, and the cent er of the opposite small side, dipped 10-15 cm under waier .

t - . '

530 MAMM /1 1. 11

RESULT S

When the electrodes were first installed and presented to the animal, without any current passing through them, the an im al hardly noticed these «obstacles» even when touching them by chance with its nose. The electrodes did not provoke any reaction or interest in the animal. W hen the current was turned on while the animal was diving, swimming, and a ,Jproaching an electrode, the animal never showed any noticeable reaction, ter med «overt response» as long as the intensity was in the naturally available range (1-10 mY /cm at the highest, assuming about the same high water conductivity in the cristallin Pyreneen tap water used as the one coming from ponds in Australi a in the study of Scheich et al. 1986). The same negative result was obtained whe n one electrode was approached to the animal's nose, even touching it rega rd less as to whether or not the pair of electrodes was connected to the generator output (the total actual current was always monitored with an electronic Ampere meter). Stimuli consisted of +I- sinusoidal or rectangular repetitive si gnals of 0 . 1 to 20Hz or simple on/offs (DC) .

The only definite reaction of the a nimal to the electrical current was a short evasive twitch to an electrical even t when 3-10 VAC or DC between the electrodes were applied and when one elect r<l de already touched or almost touched the nose or skin of the animal (maximal field intensity then available in the range of I V /cm = 40-60 dB above natura lly possible electrical fields). But even at these intensities, the animal did not get excited or significantly affected in its actual exploring or (prey-) catching b..:havior at all.

The same negative result was obtained in three other experimental sessions after the animal having been completely habi tuated to the situation : slight electri­cal shock reactions at «unphysiological » sti mulus strengths which could be also clearly perceived by the human observe r •1· ith his tongue (galvanic electricity) . The lowest threshold of the experimenter :·o r electricity produced by the set -up as used to stimulate the animal, turned out 10 be about 140 mY measured between the two electrodes touching the wet tongue and was therefore 15-20 dB lower than that of the Desman. The experimenter ' s threshold increased by 10 to 20 dB when one electrode was placed in the water as well as one hand and the other electrode again touched his tongue.

DISCUSS IO N

This latter eventual difference in sens .t iv ity between the Desman and man may be mainly due to the lower effect ive current density in the case o f the Desman under water (shunt resistance). But in conclusion, these preliminary stu­dies on the Desman should have shown up ~ >me hints of its possible electrosensiti­vity. After all, it seems rather excluded t h ~t t sensitivity to electric fielu s in the naturally available intensity range could ;, t ill be possible. If there was reall y any biological significance for an electrila l sensitivity in the context of prey detection and catching in the Desman, it should have shown up in this study

FI F.CTROSENSITIVITY IN DESMAN 531

with the kind of electrical stimuli applied as a rather obvious overt response which was not at all evident. On the other hand , the animal could certainly be trained to electric current stimuli and this would presumably somewhat lower its reaction threshold but would most likely still need much higher intensity ranges than found in its normal natural environment.

CONCLUSION

Thus, at least the Desman but presumably all mammals as well, with the exception of the Monotremata (Platypus), most likely possess no sixth sense, the electrical one. We therefore dare to consider it as almost impossible that any other (higher) mammal, reptile, or bird has achieved, during evolution, an electrical sense by slightly modifying receptors or nerves adapted to other modali ­ties such as mechanical or chemical (Platypus may therefore remain the unique exception) . Both senses are highly developped in ·the Desman's proboscis being a nocturnal and not visual animal.

Certain ecological constraints which could apply to the Desman does not seem to have a selective effect yet concerning electro-sensitivity of this insectivore. This is neither evident nor proved concerning other higher vertebrates . Without speaking of the visual and the electrical sense, it becomes increasingly more interesting to look at the Desman's auditory capabilities under water which could be useful for orientation and prey detection, not to speak ot tactile sense which is of primary importance under water (Richard 1982) .

ACKNOWLEDGEMENTS

We would like to thank Mrs Richard for her help during the experimcnls and valuable suggestions to the text and particularly to the English . We also !hank Dr . Ch. Juberthic for inviting PAS and for providing help and facilities to carry out the experiments . We are particularly indepted to R. Techene for help concerning the set-up and to A. Copain for the generous donation of maggots as the most convenient and favoured food of the Desman.

BIBLIOGRAPHY

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BAUCHOl . R .. C. BUISSERET, V. LEROY and P.B. RICHARD, 1973.- l. 'equipement senso­riel de la trompe du Dr,p·~a n des Pyrenees (Galemys pyrenaicus). Mammalia, 37: 17 -24.

Gt tL LO<.K. r .H.A., 1974. -General introduction, In: Handbook of sensory physiology, vo l. 111 / 3, Fessard, A. (ed .) : l- l2. Springer, Berlin .

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BULLOCK, T.H .A. and W . HEILIGENBERG, 1986. - Electroreception, Wiley, New York (1986).

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FRITZSCH, B. and U. WAHNSCHAFFE, 1983. - T he electroreceptive ampullary organs of urodeles. Cell Tissue Res. , 229: 483-503.

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Effects of elephant browsing on the vegetation in Kalamaloue National Park, Cameroon

by M .N. TCHAMBA and H . MAHAMAT

Center for Environmental Study and Development In Cameroon

P.O. Box 410 Maroua, Cameroon

Summary. - The Kalamaloue National Park was sampled by means of line transects to assess damage to trees caused by elephants in the dry season . A total of 2602 trees was examined of which 53 llfo were damaged (less than three-quarters browsed) and 44 llfo were dead (three-quarters browsed or more) . Most mature trees were dead (77 llfo). Ninety­five per cent of trees in the regeneration class were damaged . Of all trees browsed the majority (57 llfo) come from the recruitment class. It is concluded that elephant damage to vegetation is serious enough to warrant management intervention .

Resume. - Les effets du broutage par les elephants dans le Pare National de Kalama­loue ont ete evalues par echantillonnage sur des transects afin d 'evaluer les degats causes ault arbres par les elephants durant la saison seche. Un total de 2 602 arbres furent examines dont 53 llfo etaient endommages et 44 llfo morts . La plupart des arbres adultes etaient morts (77 IIJo ). Quatre-vingt quinze pour cent des arbres de la classe de regeneration etaient endommages. Parmi les arbres broutes la majorite (57 llfo) appartenait a la classe des immatures. 11 est conclu que les degats causes a la vegetation par les elephants sont suffisamment graves pour justifier une intervention.

INTRODUCTION

The Waza-Logone floodplain of northern Cameroon in which the Kalamaloue National Park is situated contains one of the largest elephant population of the so udan o-sahelian region . The expansion of agricultural land and wood cutting acti vi ties has resulted in an apparent maldistribution of people with respect to elephant herds, and changes of elephant migr~tion patterns . Since elephants are free to move, they migrate between Waza National Park and Kalamaloue National

Mammalia, I. 56, n • 4, 1992.