Date of Award

11-1974

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

Supervisor

Professor B. G. Galef, Jr.

Abstract

Mongolian gerbils (Meriones unguiculatus) living in their natural habitat flee to their burrows and footthump in response to the appearance of humans, while conspecific individuals reared in open-laboratory cages approach and investigate humans attempting to handle them. The present series of investigations was undertaken to determine the role of the differences in the physical rearing environment of laboratory- and wild-born gerbils in the development of their response to the visual stimuli provided by humans.

A testing procedure was developed to quantify the response of gerbils to the sudden presentation of a human-like visual stimulus and the behaviour of gerbils reared under a variety of conditions assessed in this test situation. It was found that gerbils reared in the laboratory, in gerbil-constructed tunnel systems, responded to the sudden presentation of human-like visual stimulus by fleeing to shelter, footthumping and remaining concealed for long periods, while many gerbils reared in open-cages responded to presentation of the stimulus by approaching and visually fixating it.

Analysis of the features of the tunnel environment responsible for the potentiation of the flight and concealment response in tunnel-reared animals revealed that the critical factor in tunnel-rearing was the provision of shelter during maturation. Neither the isolation from illumination nor the isolation from stimuli associated with human handlers, resulting from rearing in a tunnel, was responsible for the observed effects of tunnel-rearing. The experience of moving in and out of cover, provided by rearing in environments having shelter available, appeared to potentiate the flight and concealment response.

Observation of behaviour in a second situation measuring reactivity, that is willingness to descend from the centerboard of a visual-cliff, revealed that the effects of rearing with shelter available were not restricted to situations involving flight to shelter in response to sudden visual stimulation. Willingness to descend from the centerboard was markedly increased by rearing in environments providing shelter.

It was further found that even a relatively brief exposure to an environment providing opportunity for flight and concealment was sufficient to potentiate the entire behavioural syndrome in open-reared gerbils. Gerbils reared in normal laboratory cages would exhibit the pattern of flight and concealment in response to sudden stimulation, normally observed in tunnel-reared gerbils, if they were places in a tunnel system for 24 hours. However, behaviour of tunnel-reared gerbils was not affected by 24-hour exposure in an open-cage.

Taken together, the results of the present experiments suggest that the syndrome of reactive behaviour exhibited by wild, as compared with laboratory-reared, gerbils is the result of differences in the physical environment in which they are reared. Experience of a sheltered area early in life, for either brief or extended periods, is sufficient to potentiate reactive behaviour in gerbils at maturity.

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