Endocrine Adaptive Mechanisms and the Physiologic Regulation of Population Growth

Environmental enrichment and crowding: Behavioral and hormonal effects

“…IT has been frequently observed that crowding animals leads to decreased reproduction, increased adrenal activity, and behavioral changes, including decreased aggression in social interaction tests and in the home cage if a sufficient period of adjustment is allowed [2,5,7,12,13,16,18,27]. However, several investigators have reported increased aggressiveness among crowded animals [9,15,28], and/or no adrenal hypertrophy [4,7,17,29,33 ].…”

Serum corticosterone concentrations in reproductively mature and inhibited deermice (Peromyscus maniculatus bairdii)

“…Early work to define the physiological basis of the regulation of size of laboratory populations of rodents focused on measures of adrenal hypertrophy, reproductive organ atrophy, decreased litter survival and diminished pregnancy and birth rates (Southwick, 1955;Christian, 1956Christian, ,1961Christian, , 1963Christian, , 1967Louch, 1956;Southwick & Bland, 1959;Thiessen & Rodgers, 1961 ;Bronson & Eleftheriou, 1963;Terman, 1969). It was proposed that ACTH was responsible for the observed adrenal hyper¬ trophy and reproductive inhibition, either through a direct inhibition of gonadotrophin secretion or indirectly through increased adrenocortical steroid production (Christian, 1963;Christian & Davis, 1964).…”

“…It was proposed that ACTH was responsible for the observed adrenal hyper¬ trophy and reproductive inhibition, either through a direct inhibition of gonadotrophin secretion or indirectly through increased adrenocortical steroid production (Christian, 1963;Christian & Davis, 1964). Support for this interpretation was derived primarily from the correlation of adrenal hyper¬ trophy with increased population density in many of the species studied (Christian, 1971a, b) and the ability of high doses of ACTH to prevent sexual maturation of prepubertal female mice (Mus musculus) (Christian, 1964).…”

Effects of crowding and intermittent isolation on gerbils (Meriones unguiculatus)

“…THERE is considerable evidence that population density influences the behavior and physiology of animals [ 2,3,15,19]. Generally, one or more aspects of reproduction are depressed, and frequently a physiological stress reaction occurs with overproduction of adrenal corticoids.…”

“…Generally, one or more aspects of reproduction are depressed, and frequently a physiological stress reaction occurs with overproduction of adrenal corticoids. These reactions occur whether or not there is overt fighting and wounding, and have therefore been attributed to "psychological" stress rather than to any physical damage [2,19]. Furthermore, in gerbils, social interactions with strange animals are less sought out and ventral gland marking is severely depressed [9,20].…”