Reproductive strategies of Dicrostonyx groenlandicus and Lemmus sibiricus in high-arctic tundra

From 1981 to 1984, a field study of reproductive strategies of Lemmus sibiricus and Dicrostonyx groenlandicus in high-arctic tundra was undertaken at Igloolik Island and the Melville Peninsula, Northwest Territories. Both species of lemmings were scarce in 1981 and 1982 and increased rapidly in abundance in 1983 and 1984. In 1983, D. groenlandicus began breeding in March under the snow, whereas L. sibiricus did not commence breeding until meltoff in early June. Breeding in L. sibiricus was coincident with the appearance of the first sprouts of Dupontia fisheri and Carex stans, two of its preferred monocotyledonous food plants. A survey of tundra plants revealed that 6-methoxybenzoxlazolinone (6-MBOA) was present in the monocotyledons that are the preferred food plants of L. sibiricus, but not in those that are not preferred. With one exception, stoloniferous species contained 6-MBOA but caespitose species did not. Dupontia fisheri showed considerable yearly variation in 6-MBOA content, consistent with low and high population years for L. sibiricus. None of the dicotyledons preferred by D. groenlandicus contained 6-MBOA. Laboratory assays demonstrated that L. sibiricus responds reproductively (increased uterine mass) to 6-MBOA, but D. groenlandicus does not. We conclude that D. groenlandicus uses photoperiod to cue its reproductive effort, while plant chemical cues are an important component of the reproductive strategy of L. sibiricus.