Graduate Thesis Or Dissertation
 

Population dynamics of Microtus canicaudus

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  • Four experimental groups were designed to examine the effects of a "greens" dietary supplement (wheat clippings), as well as individual versus group-housing, on the adrenal and reproductive physiology of Microtus canicaudus. Organ culture of adrenal glands, thin-layer chromatography, and fluorescence analysis of steroid-containing medium were used to quantitatively assess adrenal function. Gravimetric data were collected for adrenal glands, testes, and reproductive tracts, as additional indices of overall reproductive condition. Males produced significantly more steroid than females for all experimental groups, probably indicative of their more aggressive nature. Group-housed males secreted more steroid than individually housed males, in both greens and no-greens groups. This relationship held for measurements of total steroid produced, as well as for individual estimates of both corticosterone plus cortisol and adrenal progesterone. Housing did not appear to affect total steroid output in females, possibly due again to their less aggressive nature. Surprisingly, group-housed females secreted significantly less progesterone than individually-housed females. Furthermore, fresh greens did not appear to affect adrenal secretion in males or females. Analysis of adrenal weights indicated a significant sexual dimorphism with female adrenal glands being heavier than male glands. Adrenal weight was not greatly influenced by either diet or housing conditions. With one exception, the supplementation of wheat clippings to a basal diet did not affect either testes or reproductive tract weights. Greens-fed females did, however, exhibit a greater percentage of individuals in an estrous condition than controls irrespective of housing conditions. Breeding experiments with M. canicaudus demonstrated an increasing mean litter size from the first through the fifth litters, followed by a slight decrease in size of subsequent litters. Additionally, the gestation period in this species was determined to be 21 days with a mean litter size of 5. 10. Results of "greens" and "density-stress" experiments support the following tentative conclusions: first, the reproductive physiology of M. canicaudus does not appear to be as sensitive to stimulation by green vegetation as reported for similar species; secondly, male M. canicaudus are more sensitive to density-imposed stress than are females; thirdly, females appeared to be more "stressed" by individual-caging than by group-caging. Thus, altered endocrine balance may play a role in regulating high density populations of this species.
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