Ontogeny of Suckling Mechanisms in Opossums (Didelphis virginiana)

Although adult mammals have several different mechanisms for drinking liquids, relatively little is known about the variation in mechanisms used by infants for suckling and how the mechanics of suckling change as a function of ontogeny. We examined suckling in infant opossums, animals that as adults use a lapping mechanism to drink. The youngest infants (45 days old) used a suction, pumping mechanism, based on dorsal/ventral tongue movements, similar to what has been documented in infant primates and pigs. However, slightly older infants (66 days old), when removed from their mother, used a lapping or licking mechanism that is closer to the anterior/posterior tongue movements that adult opossums use during drinking. Littermates remaining with the mother continued to use the pumping mechanism observed in the youngest animals. These older animals lacked teeth and were not physiologically mature enough to live independently of their mothers. We conclude that the neural controls for two distinct feeding mechanisms exist simultaneously in infant opossums and that the change from a suckling, infantile motor pattern to an adult lapping one is not strictly a temporal change.