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Acta Zoo/. Fennica 173:255-258. 1985

The sensorial world of the Pyrenean desman, Galemys pyrenaicus

P.B. Richard

Richard, P.B. 1985: The sensorial world of the Pyrenean desman, Galemys pyr~liaiCUJ . - Acta Zool. Fennica 173:255-258. The Pyrenca n dc,man is a small (56 g) in sectivore from the Iberian peninsula, particularl y the French Pyrenees. 11 li ves in mountain torrents at an altitude over 400 m. lis lri nship wi th moles (Talpa) goes back to the Eocenc. lt is an exclusively aquatic animal with strong specialisations, blindness for example. Highly developed tactile sense together with abundant food resources in the environmen1 explain its success. P. B. Richard. Laboratoire Sou terrain. Moulis, F-09200 Saint-Girons. France.

1. Introduction 2. Food

The Pyrenean desman, Gnlemys pyrenaicus, is only T he Pyrenean desman feeds almost exlusively on known fro m the northern side of the Pyrenees and some animals from the river bottom; these are p redominantly mountains of Spain (M . Cantabriques, Leon, Sa. de arthropods such as larvae of Ephemeroptera, Plecoptera Gredos, Sa. de Guadarrama) and Portugal (Minho, and Gamma ridae. The animal also coll ects food fa ll ing Douro and around Coimbra). Although discovered as into the water from river banks, viz. mollu cs, worms early as 1825, thi s species has the reputation of being and spiders. All this represents an import· nt biomass: difficul t to keep in captivit y and very few studies are every I 00 m of a small Pyrenean river produces a drift of avail able on it. I have kept desmans in captivity for up to 50 to 60 kg per day. The females, which control about two years, but they have not reproduced under the 300 metres of torrent, then have at least 150 kg of drift at conditions provided. their disposal, whilst the more vagile male has much The desman belongs to the Talpidae group but it more. probably separated from the common stem in the Eocene period. Its small size, solitary life and mountain bi otope di tinguish it from another desman, Desmana 3. O rientation moschata, whose ancestors spread all over Europe as far as France in the wes t, but which today is confined to No reliable observer can cl aim to have seen a desman southern Russia. in its natural environment (torrents) at night. The The Pyrenea n desman resembles Ta/pa europaea in desma n leaves no trace at all in the rocky torrents size, colour and form, but it has a long, stronger and although in captivity it marks its territory with excn.t:J more mobile snout, and a tail which is longer than the and with its anal and subcaudal secretions. Fift y- n i n ~o ..:·."(,{~ .. body. The forelegs have sharp, long and curved claws to animals ringed and later kept in partial captivity for up grip hold of rocks and to withstand the pres ure of water to two years have taught us more about their curre nts in torrents. The hind legs are large and movements, about the si ze of the territories of the sexes completely webbed. Like the fore legs, they have a fringe and about their periods of activity. of very stiff hairs on th e external edges. The thigh is Being partially adapted to subterranean life, the short and the articulati on of the femur gives ample scope desman actually lives in an agitated aquatic environment for leg movement, thereby facilitating rapid swimming where it has to find its food from the bottom. Us in g a under water. As in the mole, the ears a nd eyes are series of simple experiments wi th two boxes (Fig. I) we invisible. The fur composed of spear-shaped hair is came to the conclusion tha t it is insensitive to visual rather coarse, but a thick down provides excellent stimuli , because it was unable to di criminate between protection against water and cold for this non­ the boxes, i.e. to find the prey. hibernating a ni mal . living in an inhospitable We a lso studied how the des man behaves in a th ree­ environment. The animal is an excellent climber in its dimensional space when searching fo r food. Prey environment, but a poor runner in open spaces. animals were presented at diffe rent levels (Fig. 2). The 256 P.B. Richard

2

Fig. I. Two transparent boxes, one of them with a mobile prey and th e other empty. The position of the boxes can be ch"nged. The desman is unable to discriminate between them. Fig. 2. Constructi on of the experimental aquarium used to presen t prey animals placed at different Je,..,Js. Fig. 3. Experimental aquarium for stud);ng choice of leve l of movements to explore or to search for food . . order of preference was: prey on the bono m, fl oating on the surface, pl aced in the middle and a few centimetres above the water. In another experiment we cut part of the experimental aquarium into two corridors, one of them with food available and the other empty (Fig. 3). Each corridor was accessible through a wall with eight holes at different levels. Statistics for entries and exi ts show that three quarters of the movements were made on or in the water, one quarter on the bottom. It was also observed that the desman makes outward exploratory journeys on the water sm:fuce but returns along the bottom. It searches for its food both on the su rface and on the bottom, but it return v.'it h its prey on the surface because it ea ts its prey out of water.

4. Tactile sense

The tactile organs, especially the "ibrissae and the Eimer's organs at the end of the snoUI are large and Fig. 4. Rosettes of Eimcr's organ, centr~ on a vestigial hair (X 120). highly complex. As in most aquatic a nimals, th e vibrissae are numerous, long and strong and immobile at their roots. Thei r innervati on is rich, the nervous 5), and certainly in the discrimination of very fine fasciculus of each vibrissa being larger than the vibri ssa particles. Detection of obstacles in the air at the same itself, more tha n three qua rters of the snout secti on distance ( 100 cm) requires the aid of other organs. being fill ed with efferent nerves of the ,;brissae. The Under water, the desmari seldom collides with obstacles latter perceive both the contact of nearby objects and the (Fig. 6). movement of passing water. Eimer's m-gans (Fig. 4), We are currentl y studyin g the desman's ability to numbering about 100 000 over a fev. mm: at the end of recognize different surfaces (Fig.. 7) and geometrical the snout, have piled-up cell structures around the nerve figures engraved on a smooth surface (Fig. 8). The ti ss ue which rises up to the epidermis. as in certain stimuli have been pl aced in t o food boxes cl osed with orga ns of the head of whales and of the bill of Platypus. lids. Only one of them can be opened to gi ve access to They are very sensitive to contact and to variati on in the food. It is this one that the desman has to recognize water pres ure caused by the m ovemen~ of the animal. although the positions of the boxes are changed at These organs are probably in volved in the detection of random. Geometric figures (Fig. 8) engraved on a obstacles in wa ter, at a di sta nce of at least 100 cm (Fig. smooth surface are easil y distinguished if they are fairly ACTA ZOOLOGICA FE 1 ICA 173

+ 0 0 u ~ \] Q + Q 0 0 D 8

Fig. 5. Experimental aquarium for stud)ing the desman's ability to detect im·isible obstacles (transp:L!Tent doors) in the water or on the surface. Fig. 6. Immersed labyrinth. Fig. 7. Discrimination of different suriace structures of the lid. Only the reinforced hd 1-) can be o perued. Fig. 8. Recognition of geo metric form:! . The stimuli(+ and -) arc stuck in relief under the handle of a: hc lid , where it is touched by the snout when opening the lid . The ( ) I..C is the only one that can be opened. Fig. 9. Vi sual(-) as opposed to chenuca.l (+)detection.

different. The height of the figure is perceived more easily than the width, the angles at the base better than 5. Chemoreception those on the top. the sides beuer than the centre, the lines better than the angles... These differences are Finding of submerged food poses a different problem. perhaps due to the manner of ta ile form exploration in It is neither a visual process nor eve n necessarily a which the extension and the d irection of the movement vibrato!) one, for imrn bile prey is found as easily as of the snout are vital. The results of our experiments mobile. at least at a hon distance. In order to study the seem to prove that in spite of its blindness the desman is possible role of the cliemical sense, the foll owing able to recognize a figure with t.be aid of its tactile sense. experiment wa set up: o boxes containing the same • 258 P.B. Richard prey were used, one of them tra nsparent to show the 6. Conclusi ns moving prey, the other opaque but p1erced wnh hole lO all ow fluids from the crushed prey to pass through (Ftg. Traces of ' ch imeri~m· can be seen in the dcsman 9). The desman visited the latte r box more frequently because it shows traces of adaptati on to two very than the former. This chemical detection seems to be different en\.i ronmcnts. lt has coloni zed torrents, thanks 'olfactory' rather than gustatory. Various arguments partly to the tactile sense which it has inherited fro m its lead us to th ink that J acobson's organ plays a role m Talpid ancestors and which par\ly compensates for It s chemoreception of liquid material. This unique loss of vision, and partly to the olfactory sense of the olfactory organ of lower vertebrates is usually absent Jacobson's organ, w.hich is highly developed in the from adult mammals, but persists in some groups, Talpidae. It-is a powerful swimmer, but it exhibits no notably the ru minants a nd insectivores. lt is particu larl y particular respiratory adaptation, and it survives in the developed in the Taipidae, so it may be involved with harsh envi nmcnt of river torrents because of the their chemical sen . However, this problem must be especia ll y rich biomass available. A slight ecological studied in greater detail. change in its very speciali zed environment would, however, cause its disappearance forever.

References

Bauchot, R., Richard, P.B. & al. 1973: L'cq uipement sensoriel de la Soc. Hist. Nat. Toulouse 47 :163-227. trompe du Desrnan des Pyrenees.- Mammal ia 37; 17-24. Rich ard , P.B_ 1973: Le Dcsman des Pyrns; Mode de vie; Univcrs Hinde, R.A. 1970: Animal behaviour.- 876 pp. McGraw Hill, N.Y. sensoriel. - Mammali a 37:1 - 16. Hutchison, J .H. 1974: Notes on the type specimens of European 1981 : 1.-'l detection des objets en milieux aquatiquc et acrien Mioccnc talpida_- Geobios 7:21 1-256. par le Desman des Pyrenees.- Bchav. Process. 6: 145- t59. Pcyrc. A t956: Ecotogic et biogi:ographic du Des man.- Mammalia Trutat, E. r :9 1: Essai sur l'histoire naturelle du Dcsman des 20:405-41 . P_ re.:.ees. - Toulouse. Pu ys cgur, C. 1935: Rtch