Adrenal Weight in a Colorado Mule Deer Population

Abstract

Weights of paired, fresh adrenals were sampled yearlong from 145 to 176 Cache la Poudre mule deer (Odocoileus hemionus), 1961-65. Annual population densities of this migratory herd xvere unknown within the S28-mile2 area of deer collections. Mean (+ SD) absolute adrenal weights svere 6.08 + 1.64 grams for 46 mature, male deer and S.15 + 1.40 grams for 80 mature, female deer. This difference was significant (P < 0.01). Significant (P < 0.05) annual changes in the mean absolute adrenal weight did not occur in either sex. A significant (P < O.OS) regression of absolute adrenal xveight on a polynomial in the day of collection, which consisted of peaks (high stress) in late January and early August and lows (low stress ) during April and mid-December, accounted for about 35 percent of the variation (R2) in absolute adrenal weight of mature males. The regression of absolute adrenal ereight of mature females on a polynomial in the day of collection was not significant (P < 0.05). Simple correlation coefficients and stepwise multiple regression analyses showed that age and age-related variables svere important sources of variation in absolute adrenal weights and that environmental variables were unimportant. LOge absolute adrenal weight could be predicted ( R2 = 0.84) in male mule deer from lOge estimated age, eviscerated carcass weight, and date of collection. Absolute adrenal weight could be predicted ( R2 = 0.75 ) in female mule deer from lOge estimated age, eviscerated carcass xveight, date of collection, and elevation of collection site. Adrenals of females had proportionately more variation associated with eviscerated carcass weight, season, and elevation at a given age than did adrenals of males. Mean relative adrenal weight did not differ significantly (P < 0.05) between sexes, ageclasses, or years. Significant seasonal changes in the mean relative adrenal zZeights of each sex appeared to be a function of variation in fat reserves. By extending Selye's ( 1946) ieory of the general adaptation syndrome, Christian (1950) hypothesized a density-dependent, behavioral endocrine feedback system that regulates populaltions of some kinds of mammals. Christian and Davis (1964:1580) reviewed and defended ffie hypothesis and concluded that the system is important in the regulation of populations of rodents, lagomorphs, deer, and possibly ather nzammals.'' The vcxluminous literature on endocrine-population relationships has been reviewed by Christian et al. ( 1965 ) . Much of this research has utilized such indices of adrenocortical activity as cholesterol content of the adrenal glanld, urine metabelites, lymphocytes or eosinophil counts of the 1 A contribution from Colorado Federal Aid Project W-105-R. 9 Present address: U. S. Forest Service, Intermountain Forest and Range Experiment Station, Boise, Idaho. blood, histologic study of ffie adrenal gland, ascorbic acid ccontent of the adrenal gland, and the absolute or relative weight of the paired adrenals to either deteot or assess the effects of various stressors on confinecl laboratol:y mammals. Several authors have analyzed adrenal sveights of free-ranging and captive deer. Browman and Sears (1956) and Taber et al. (1960) studied mule deer, Hughes and Mall (1958) blacktailed deer ( Odocoi1zas 7xem?onus columbianus), NVelch ( 1962) and Hoffman and Robinson (1966) rvhite-tailed deer (Odocoileus virginulnus ), Wandeler ( 1966 ) and Bubenik an!d Bubenik ( 1967 ) roe deer (Capreolus capreolus), Christian (3t al. (1960) sika deer (Cerous nippon), and Flook (1970) wapiti (Certuscanadensis). Welch ( 1962 :100 ) suggested that annual trends ill mean adrenal sveights, presumably as sampled during the hunting season, rnay furnish a useful supplementary index of condition