The Effects of Social Rank on Reproductive Indices in Groups of Male Collared Lemmings (Dicrostonyx groenlandicus)

Long-term physiological effects of social rank were examined in groups of male collared lemmings, Dicrostonyx groenlandicus. For 9–13 weeks, adult lemmings were caged together in groups of 3, or caged singly as controls. Social ranks were assigned to each member of each triad on the basis of behavioral data. At the end of the experiment, dominant animals had significantly higher plasma testosterone levels than either the active and passive subordinates or controls. Seminal vesicles of dominant lemmings were significantly heavier than those of either subordinate group. Histological examination of the testes showed deficiencies in spermatogenesis in 7 of the 21 active subordinates. However, all 18 control males, 20 of the 21 dominant and 20 of the 21 passive subordinate males had normal spermatogenesis. No significant adrenal weight differences were found among grouped animals of different ranks. The experiment demonstrated not only long-term effects of rank on plasma testosterone concentrations but also effects of rank on spermatogenesis in lemmings.