Date of Award

1-1-1980

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

Hibernation in Richardson's ground squirrels, Spermophilus richardsonii richardsonii, was studied for three winters. Animals were maintained at 5(DEGREES) (+OR-) 2(DEGREES)C and continuous light (LL) during the first winter and at 5(DEGREES) (+OR-) 2(DEGREES)C and continuous darkness (DD) during the second and third winters. The typical ground squirrel hibernation pattern was observed throughout the study although the duration of the total and individual hibernation bouts was shorter than that reported in the field.Histological analyses of the gonads during hibernation indicated a greater amount of gonadotropic activity in male ground squirrels than in female ground squirrels. Mature spermatozoa were observed in male testes in January whereas follicular maturation in females did not commence until after terminal arousal in March.Pineal gland hydroxyindole-O-methyltransferase (HIOMT) activity was low during the annual hibernation cycle regardless of the sex and metabolic condition of the animal. HIOMT activity increased following terminal arousal and was higher in field animals during the breeding season than in hibernating laboratory animals.Results of daily subcutaneous injections of pregnant mare serum (PMS) (1 IU/50 gm B.W. and 1 IU/100 gm B.W.) suggest that male ground squirrels are more susceptible to gonadotropic hormone stimulation during hibernation than female ground squirrels. This provides a possible physiological explanation for field observations of the earlier emergence and sexual maturity of males than that of females.Daily subcutaneous injection of melatonin (25 (mu)g/100 gm B.W. and 50 (mu)g/100 gm B.W.) failed to affect hibernation, gametogenesis, or axilla brown fat deposition and composition in ground squirrels. The pineal gland in ground squirrels, a nonphotoperiodic animal, does not appear to participate in the regulation of hibernation or reproduction.

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