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 unde rtaken at Igloolik Island and the Melville Peninsula, Northwest Territ ories. Both species of lemmings were scarce in 1981 and 1982 and incre ased rapidly in abundance in 1983 and 1984. In 1983, D. groenlandicus began breeding in March under the snow, whereas L. sibiricus did not c ommence breeding until meltoff in early June. Breeding in L. sibiricus was coincident with the appearance of the first sprouts of Dupontia f isheri and Carer stans, two of its preferred monocotyledonous food pla nts. A survey of tundra plants revealed that 6-methoxybenzoxlazolinone (6-MBOA) was present in the monocotyledons that are the preferred foo d plants of L. sibiricus, but not in those that are not preferred. Wit h one exception, stoloniferous species contained 6-MBOA but caespitose species did not. Dupontia fisheri showed considerable yearly variatio n 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 res ponds reproductively (increased uterine mass) to 6-MBOA, but D. groenl andicus does not. We conclude that D. groenlandicus uses photoperiod t o cue its reproductive effort, while plant chemical cues are an import ant component of the reproductive strategy of L. sibiricus.