Pregnancy-block in Microtus agrestis and Induced Ovulator

Pregnancy blocking in the vole, Microtus agrestis

“…The nature of the phenomenon also suggests that it may have a role in controlling population density (Chipman, Holt & Fox, 1966;Clulow & Clarke, 1968 ;Whitten & Bronson, 1970), and Mallory (1972) has suggested that pregnancy blocking may be involved in the population fluctuations of microtine rodents. A number of variables, however, may affect the importance of pregnancy blocking to animal populations in the wild : in mice, laboratory experiments indicate that some strains are more susceptible than others (Chapman & Whitten, 1969) and that blocking effectiveness may be reduced by grouping the females (Bruce, 1963), pre-exposing the females to many males, or the continued presence of the stud male (Parkes & Bruce, 1962).…”

“…The pregnancy-blocking effect of a strange male has also been demonstrated in Peromyscus maniculatus (Eleftheriou, Bronson & Zarrow, 1962), Microtus agrestis (Clulow & Clarke, 1968), and M. pennsylvanicus (Clulow & Langford, 1971). In addition, there is suggestive evidence for the phenomenon in Clethrionomys glareolus (Clarke & Clulow, 1973).…”

Evidence for a coitally induced 'mnemonic' involved in luteal function in the vole (Microtus agrestis)

“…This question of how the act of mating by the stud male vole stimulates luteal function also raises the question of how a 'strange' male (i.e. a male other than the stud) blocks luteal function and pregnancy in newly mated females (Clulow & Clarke, 1968). This phenomenon was first observed in the mouse (Bruce, 1959), but has since been demonstrated in the deermouse (Peromyscus maniculatus: Eleftheriou, Bronson & Zarrow, 1962) and a number of microtine rodents (Clulow & Langford, 1971;Stehn & Richmond, 1975;Mallory & Brooks, 1978).…”

Pregnancy blockage and the memory of the stud male in the vole (Microtus agrestis)

“…The effect is primarily due to a failure of luteal function (Dominic, 1970;Milligan, 1976b) and can also be demonstrated in pseudopregnant females (Dominic, 1966). The phenomenon was first observed in the mouse (Bruce, 1959), but has since been demonstrated in the deermouse (Peromyscus maniculatus: Eleftheriou, Bronson & Zarrow, 1962) and a number of microtine species (Clulow & Clarke, 1968;Clulow & Langford, 1971;Stehn & Richmond, 1975;Mallory & Brooks, 1978). Pheromones in the urine are believed to be the effective stimuli mediating the response in mice (Dominic, 1966), although whether the same is true for other species is uncertain.…”