Endocrine adjustments in a wild lemming population during the 1969 summer season

Abstract

1. 1. Wild-caught and laboratory-reared, group-housed brown lemming ( Lemmus trimucronatus) were compared regarding pituitary-adrenal and gonadal function. 2. 2. Early trapping periods yielded higher numbers of animals (for equivalent effort) than did later periods; animals which emerged from the snow in June displayed marked adrenal hypertrophy, high basal levels of adrenal steroid secretion, high pituitary ACTH content, and lower sensitivities to exogenous ACTH. 3. 3. Females were less sensitive to adrenal stimulation than were males, and had lower pituitary ACTH content; gravid females were particularly resistant to both ACTH effects and effects of climate and social pressure. 4. 4. Differential mortality of males was revealed by the trapping regimen, and this mortality was consistent with signs of stress (adrenal hyperfunction, cardiac hypertrophy and renal disease) which were more pronounced in males. 5. 5. It was concluded that both physical environmental and social environmental changes modify endocrine balance in wild lemming populations, and that the endocrine status of the population markedly affects both input and output phases of population dynamics. 6. 6. Gross pathological changes which may contribute to mortality are discussed.