Department of Ecology, Ethology and Evolution, University of Illinois, Urbana, Illinois 61801, U.S.A.
(Received 10th September 1974)
The rate of sexual maturation in females has been shown to be related to population density in a number of species of small wild rodents (Microtus californicus: Greenwald, 1957; Mus musculus: Southwick, 1958; Rowe, Taylor & Chudley, 1964; Microtus ochrogaster and M. pennsylvanicus: Keller & Krebs, 1970; Lemmus trimucronatus and Dicrostonyx groenlandicus: Krebs, 1964). It has been shown in the laboratory that the presence of an adult male accelerates the rate of sexual maturation in young female mice (Vandenbergh, 1967; Castro, 1967; Fullerton & Crowley, 1971), prairie voles (Hasler & Nalbandov, 1974) and cuis, Galea musteloides (Weir, 1973).
In this study, the influence of adult male collared lemmings (Dicrostonyx groenlandicus) on the rate of sexual maturation after weaning of juvenile females was investigated. The animals were laboratory-born descendants of lemmings captured near Fort