Behavioural mechanisms underlying infant care in male and female Mongolian gerbils
The introduction of parental behaviour in naive animals has been studied in several species. Male and female adult Mongolian gerbils, Meriones unguiculatus were singly exposed to protected pups (PP exposures). Exposures lasted for ten minutes, and were carried out each day. Behaviour patterns shown by the adults were recorded, and their frequencies measured. After several PP exposures (3-18), adults were exposed to unprotected pups (UP exposures) in order to detect whether or not the normal aggressive response to pups was still present, or had been overcome and replaced by parental responsiveness. Preliminary experiments showed the aggressive response could be overcome in as little as five ten minute exposures. A variety of parental behaviour patterns were shown by some individuals, suggesting that stages may exist in the process under investigation. Following on from preliminary experiments, the effect of increasing the number of both PP and UP exposures was investigated. Increasing PP and UP exposures increased the percentage of animals responding non-aggressively towards pups. However no increase was seen in the range of parental responses shown. Again, results suggested the development of the parental response was a non-unitary process occurring in stages: first the overcoming of fear of pups or aggression towards pups; second, investigation of the pup; third, the development of parental responsiveness. The role of olfactory and auditory cues from the pups were next investigated. If a pup bore the scent gland sebum of the experimental adult, aggression was overcome more quickly than before. Also, more parental behaviour patterns were shown. If the pup bore the experimental adult's urine, aggression was overcome more quickly than in preliminary experiments, but not as quickly as when the pups bore the adult's sebum. No correlation was found between the rate of ultrasonic calling and the rate of the induction of parental responsiveness. This was thought to be an artefact of the recording procedure, since the source of individual calls was not identified, and the frequency of calls could therefore have been increased due to adults calling. Parental responsiveness appeared to be maintained 2 weeks after its induction, but not 10 weeks after induction. An exception to this was the animals exposed to pups smeared with the experimental adults sebum, who did not appear to maintain responsiveness even up to 2 weeks after induction. Overall twice as many males as females were able to be induced to show parental responsiveness. Males overcame their aggression to pups, and showed parental responsiveness more quickly than females did. Further work arising from the present studies would include a more detailed study of both the influence of ultrasonic calling by pups on the development of parental responsiveness and the quicker development of parental responsiveness found when pups bore an odour familiar to the adults.