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Date of Award

10-1976

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

Supervisor

Professor B.G. Galef

Abstract

Following parturition, the female golden hamster (Mesocricetus auratus, Waterhouse, 1839) exhibits a broad repertoire of maternal behaviours essential for the growth and protection of her developing offspring. In addition to engaging in obviously nurturent activities, the maternal hamster exhibits a behaviour infrequently observed in other species: she almost invariably cannibalizes some of her own live offspring.

Hamster pup cannibalism has been characterized in the literature as a breakdown of normal maternal behaviour, resulting from a variety of possibly stressful conditions imposed upon the mother (for example, disturbance following parturition). The influence of such factors on frequency of pup destruction, however, has not been empirically examined, and, in fact, no systematic observation of hamster pup cannibalism has been reported in the literature.

The major purposes of this thesis were to provide normative data on the frequency, extent, and time course of cannibalism by hamsters rearing their litters under standard laboratory conditions, and to determine the proximal stimulation controlling the onset, maintenance, and cessation of this behaviour.

Systematic observations of 63 litters born to 21 mother indicated that there is a high probability (.75) of a mother exhibiting some cannibalism toward her young, but that each mother destroys only a few of her pups. Eighty percent of this destruction occurs within five days of parturition, and cannibalism is directed apparently randomly towards the pups present in the litter. While an individual hamster does not reliably cannibalize a certain number of pups, she does exhibit relative constancy in the number of pups she rears over successive litters.

Experimental results indicated that the pup cannibalism normally exhibited by the hamster is not dependent upon the presence of the possibly stressful conditions suggested in the literature. Instead, the results provided evidence that the initiation of pup cannibalism is systematically controlled by a variety of stimuli which reflect the size of the litter, including olfactory stimulation and stimulation received during nursing.

Each hamster apparently cannibalizes to regulate her litters at a particular size. If litter size is artificially reduced by removing pups from the litter, the mother reduces cannibalism proportionally. If litter size is increased on the day of parturition, by giving the mother newborn foster pups, she will exhibit a compensatory increase in cannibalism. The probability of observing this compensatory increase in cannibalism in response to artificial litter size increment decreases as a function of increasing time postpartum at which litter size is altered. The change in responsiveness to litter size was found to be a results of internal changes in the mother occurring as a function of time postpartum, rather than from changing stimuli received from pups increasing in age.

Variations between individual mothers in the number of pups they rear per litter probably results from long-term constancies in their relative capacity to conceive, deliver, and/or successfully maintain young. The observation that hamster consistently gives birth to more pups than she will rear, and achieves a reduction in number of pups by an active culling of the litter, suggests that pup cannibalism enables the mother to alter the size of her litter to that size most compatible with her capacity to rear young under specific environmental conditions.

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