Skin and gland but not urine odours elicit conspicuous investigation by female grey short-tailed opossums, Monodelphis domestica

Chemical communication plays a major role in mammalian behaviour. One mammal with well-developed chemical senses is the grey short-tailed opossum, a small, South American marsupial that has become common in laboratory research. Male and female opossums scent-mark with different body parts, but apparently not with urine, and females enter oestrus following their exposure to male odours. To elucidate the effects of body odours on the behaviour of female opossums, we investigated their ability to discriminate between conspecific odours originating from different body parts. We simultaneously presented female opossums with two cotton balls smeared either with skin and glandular secretions or urine of conspecifics, or with distilled water or blank controls, and we analysed the time females spent investigating each stimulus. Odours of the male suprasternal gland elicited intensive investigation by the test females. Male flank and submandible odours, and female submandible odours, were also attractive to the females. Investigation of male and female urine was comparable to investigation of water and blank controls. We suggest that in this species, which inhabits semiarid areas, urine marking is avoided to reduce dehydration, and consequently urine has lost its biological significance as a chemosignal. On the other hand, glandular and skin secretions, which are more stable than aqueous deposits in dry conditions, allow the opossums to communicate with each other effectively and also to retain body fluids.