Adrenal Gland Responses to Experimental Manipulations of Captive Pocket Gophers (Thomomys umbrinus)

Abstract

The responses of the adrenal gland in two populations of the pocket gopher, Thomomys umbrinus , held in captivity were gauged after (1) holding individuals singly in captivity; (2) placing them together in various sex and numerical combinations and (3) surgical removal of the left adrenal gland. Animals held singly in captivity showed only slight increases in adrenal weight, apparently due to nodular increase of the zona fasciculata. Unilaterally adrenalectomized animals (kept singly) showed a marked compensatory hypertrophy of the remaining right adrenal gland due to both cortical and medullary changes. Animals held together in “pairs” normally reacted to each other by violent threats and attacks reflected in frequent wounding and death and in pronounced medullary changes. Populations of 2, 4 and 8 individuals held in outdoor pens with “natural” food and cover showed striking antagonisms at the higher levels, including death to half the test population at level eight, but did not show adrenal gland differences consonant with the extent of wounding, weight loss and death. Cellular changes in the adrenal gland were chiefly medullary. In view of the unusual gland responses observed we suggest that the pocket gopher depends on medulla-mediated antagonisms to maintain territory reinforced by ecological isolation. Apparently little dependence is placed on adrenopituitary interactions. The pocket gopher seemingly has lost, or has never developed, dependence on this axis so important in more social mammals.