The Role of Olfaction at Birth in Marsupial and Monotreme Mammals

Abstract

At birth all mammalian neonates depend on finding the milk source in order to survive. The development of mammalian young ranges from precocial to highly altricial, but olfaction plays an essential role in the milk-finding process in all mammalian species studied, along with other sets of cues depending on the development of the neonate's sensory systems. Of all mammals studied, so far marsupials and monotreme are the least developed at birth and have the least developed olfactory systems. Nonetheless the neonates are able to reach the pouch and the teat or milk patches unaided by their mothers. Behavioural studies con firm that olfaction pays a role in guiding the young to the pouch and teat and may be responsible for the switch in direction at the lip of the pouch in the tammar wallaby to climb down into the pouch and attach to a teat. The switch in direction at the pouch entrance may be triggered by olfactory cues acting via this the main olfactory system, as it is further developed than the accessory olfactory system. However, the latter may serve as a backup if the main olfactory system fails. How the information is processed by the poorly developed neonatal brain to control the movements and behaviour of marsupial and monotreme young remains to be investigated.