In a replicated experiment, nonbreeding winter populations of Microtus montanus were given supplements of rolled oats coated with 6-methoxybenzoxazolinone, a naturally occurring plant derivative. After 3 weeks of this feeding regime, samples from the populations demonstrated a high incidence of pregnancy in females and testicular hypertrophy in males. Control populations receiving rolled oats coated only with the solvent showed no reproductive activity. These results demonstrate that the presence of 6-methoxybenzoxazolinone in the plant food resource acts as the ultimate cue to trigger reproductive effort in Microtus montanus.

No abstract

A plant-derived cyclic carbamate, 6-methoxybenzoxazolinone, that stimulates reproductive activity in Microtus montanus has been isolated. This nonestrogenic compound may be a naturally occurring environmental cue affecting reproductive cycles in many mammals.

From 1987 to 1989, the cohort dynamics of Microtus montanus populations were studied at two montane meadow sites approximately 160 km apart, in northwestern Wyoming. The 1987 and 1988 breeding seasons differed markedly from each other. In 1987, melt off occurred in April, and the first cohort was born in May (cohort 1). The entire breeding season was favorable owing to frequent rainfall throughout the summer. Cohort 1 animals grew rapidly and females began breeding at 4–5 weeks of age. Likewise, cohort 2 (June) animals exhibited rapid growth and females were breeding at 7–8 weeks of age. Cohort 3 (July and August) animals grew more slowly and most entered the winter as prepubertal animals of subadult size. At the end of the summer, cohort 3 animals represented >70% of the voles recruited during the breeding season. In 1988, following melt off in late April, precipitation was below normal and the situation intensified to severe drought through the summer. The growth rates of cohort 1 and 2 animals were significantly lower than 1987 growth rates, and very few females attained sexual maturity. At the end of the summer, cohort 3 animals represented <25% of the total recruitment at both study sites. Such apparent phenotypic plasticity of growth and maturation appears to be an evolved adaptive strategy that is responsive to several environmental cues. Both study sites, although widely separated, exhibited virtually identical patterns throughout the study.