BENNETT, V.A.*; KUKAL, O.; LEE, R.E.: Seasonal metabolic depression and mitochondrial degradation in Arctic woollybear caterpillars, Gynaephora groenlandica

Gynaephora groenlandica requires 7-14 years to complete its life cycle, overwintering as many times. Because of the short active season (3-4 weeks in June), these caterpillars may spend as much as 90% of their lives in dormancy without feeding. Therefore energy conservation is especially important for their survival in this extreme environment. At the end of June, when the majority of arctic insects are just beginning their summer active period, G. groenlandica caterpillars enter hibernation, probably as a means of temporally avoiding parasitoids. Therefore, even in hibernation, G. groenlandica experience the warmest summer temperatures in July and early August that could potentially elevate metabolic rate causing depletion of energy reserves. To conserve energy, G. groenlandica exhibit a seasonal metabolic depression associated with hibernation: respiration rates of late-season caterpillars were as much as 50% lower than those of active caterpillars, and they were relatively insensitive to temperature (Q₁₀~1.5). A previous study demonstrated that cold-acclimated G. groenlandica had fewer mitochondria in brain and fat body tissues than warm-acclimated caterpillars. Could this mitochondrial degradation be the mechanism of metabolic depression? Using confocal microscopy and digital image analysis, mitochondria were quantified in tissues of both active and hibernating stages of G. groenlandica. Initial data show a 54% reduction in the number of mitochondria in fat body tissue of hibernating versus active caterpillars, and as much as a 65% reduction in the number of mitochondria in muscle tissue.