METABOLIC-RATE CHANGES PROPORTIONALLY TO CIRCADIAN FREQUENCY IN TAU-MUTANT SYRIAN-HAMSTERS

The tau mutation in Syrian hamsters (Mesocricetus auratus) is phenotyp ically expressed in a period of the circadian rhythm of about 20 h in homozygotes (SS) and about 22 h in heterozygotes (S+). The authors inv estigate whether this well-defined model for variation in circadian pe riod exhibits associated changes in energy metabolism. In hamsters of the three genotypes (SS, S+, and wild type [WT]), oxygen consumption m easurements were performed at 28 degrees C (thermoneutral), 18 degrees C, and (after acclimatization) 10 degrees C. After correction for bod y mass, SS tau mutant hamsters had a higher overall metabolic rate (av erage oxygen consumption per hour over 24 h) and a higher resting meta bolic rate (the lowest 30-min oxygen consumption in the subjective day ) than did WT hamsters at all ambient temperatures. S+ hamsters were i ntermediate in both after taking body mass into account. The differenc es in metabolism among the three genotypes indicate that the increase in metabolic rate was statistically indistinguishable from a proportio nal increase in circadian frequency. The oxygen consumption totals per circadian cycle (24 h for WT, 22 h for S+, and 20 h for SS mutants) w ere not statistically different among the genotypes after correcting f or body mass. The possible roles of pleiotropic effects, of linkage to genes involved in growth and metabolism and of early ontogenetic infl uences are briefly discussed.