Effect of Population Size on the Weights of the Reproductive Organs of White Mice

Abstract

Male white mice were placed in small cages in groups of 4, 8, 16, and 32, following 3 weeks of isolation. After 1 week all mice were killed. The fixed weights of the preputial, thymus, and adrenal glands, seminal vesicles, and testes were obtained and compared to those from mice kept in isolation. There was an inverse relationship between population size and the weights of the preputial glands and seminal vesicles. Preputial glands decreased a maximum 38% and seminal vesicles 40% below the isolated control weights in populations of 32 mice. Adrenal glands increased with increasing population size to a maximum of 9% over the mean control weight in populations of 16 mice. At 32 mice/cage there was a decline in adrenal weight from the maximum. Body weight declined with increased population size, a decline paralleled by the weight of the testes. Correcting the organ weights for body weight exaggerated the adrenal changes, did not affect the preputial or seminal vesicles changes, and obliterated the testicular weight changes. The thymus exhibited no significant changes in weight. A decline in reproductive function and increase in adrenocorticotrophic function was attributed to stress resulting from increasing population pressures with increasing population size.