MOLE-RAT HARDERIAN-GLAND SECRETIONS INHIBIT AGGRESSION

The harderian gland secretions of mole-rats, Spalax ehrenbergi, usuall y released by self-grooming, include odorous substances which are sex dependent. Male secretions were the most attractive to both sexes, whi le female secretions were attractive to males but not to other females . The rate of attacks by females towards intact males was higher than towards males whose harderian gland had been removed. However, groomin g by intact male mole-rats decreased the rate of attacks by their oppo nents, while grooming by males without harderian glands did not; thus the male harderian secretions appear to have appeasement qualities. Gr ooming by females with and without harderian glands failed to reduce a ggression. Unlike intact males, those without harderian glands had alm ost no volatiles on their fur, and thus are probably not considered to be a threat to conspecifics. Gas chromatography spectra showed that s ubstances of harderian origin were added to the fur during grooming. S ome of these substances remained on the fur long after the animal ceas ed grooming, and appear to give the animal its specific odour, but som e volatile substances peaked briefly after grooming, and were probably responsible for the decline of aggression that occurred after groomin g. Although grooming has long been considered to be a displacement act ivity, we suggest that in the mole-rat its performance is too risky to be merely this, and it has acquired the meaning of appeasement throug h the release of chemical cues. (C) 1997 The Association for the Study of Animal Behaviour.