GROOMING EXPRESSES HARDERIAN-GLAND MATERIALS IN THE BLIND MOLE-RAT

The blind mole rat (Spalax ehrenbergi) is a highly aggressive and soli tary rodent that shows the most striking physiological and behavioral adaptations to underground life. The eyes are not detectable externall y; they are atrophied and covered by a thick layer of skin. A consider able part of the orbit is occupied by a very large Harderian gland. Th e current study demonstrates that during autogrooming the mole rat exp resses Harderian gland materials from the conjunctival sat to the exte rnal nares and spreads them onto the fur. In contrast to other rodents , the mole rat's grooming behavior is usually confined to the front pa rt of the body and does not progress after the head wipes to ventrolat eral torso licking, Moreover, in highly aggressive encounters grooming sometimes ceases after the second phase-the nose wipe bouts, The uniq ue first phase of the mole rat's grooming consists of highly rapid str okes over the skinny border of the head, which we assume help to squee ze Harderian materials from the gland, Unlike other rodents, in which grooming occupies a considerable part of their waking time, mole rats, cage individually, rarely perform autogrooming behavior, Grooming in mole rats has been found to be highly correlated with aggressive encou nters, and submissive animals exhibit significantly more grooming than their dominant opponents, It is speculated that the Harderian gland d ischarge may serve as an appeasing substance when mole rats meet to re duce the extreme aggressiveness typical of these subterranean rodents. (C) 1995 Wiley-Liss, Inc.