Ecological physiology of the Arctic woollybear caterpillar Gynaephora groenlandica (Lepidoptera: Lymantriidae).

摘要

Gynaephora groenlandica caterpillars are active for only 3–4 weeks each summer, becoming dormant in late June when they spin silk overwintering structures (hibernacula) anchored at the base of rocks. Survival depends on selection of appropriate overwintering microhabitats and physiological tolerance of conditions within hibernacula. Hibernaculum sites were became snowfree first, allowing caterpillars to emerge early in spring and begin foraging. Mean monthly hibernaculum temperatures were 0.75°C warmer than surface temperatures, but were more thermally stable on a daily basis in late summer. A distinct pattern of hibernaculum distribution around rocks suggests that caterpillars key in on some microhabitat feature(s), although behavioral preferences for microhabitat selection remain unclear.; Overwintering insects must survive desiccation stress as well as cold. Water loss rates decreased in hibernating caterpillars compared to active ones in temperate Pyrrharctia isabella, but not in G. groenlandica. The ratio of water lost to CO₂ released, reflecting the magnitude of respiratory water loss, was significantly lower in G. groenlandica than in P. isabella, suggesting that G. groenlandica are well-adapted to desiccating conditions. Dense setae provided a boundary layer of still air around the cuticle surface, decreasing evaporative water loss. Setae significantly reduced the effects of convection on cuticular water loss in G. groenlandica. Gynaephora groenlandica's water loss rates were lowest under simulated hibernaculum conditions of low temperature and high relative humidity.; Mitochondria are involved in seasonal metabolic depression to conserve energy during dormancy. As determined by confocal fluorescence microscopy, fewer active mitochondria were present in fat body and muscle tissue of hibernating G. groenlandica compared to active caterpillars. Fewer copies of mitochondrially encoded genes (cytochrome oxidase I and 16S ribosomal RNA) were observed in dormant caterpillars, indicating that during dormancy there were either fewer mitochondria (indicative of structural degradation), or fewer copies of the genome per mitochondrion. There was no apparent difference between active and dormant caterpillars in the level of RNA products from mitochondrial genes, suggesting that mitochondrial function was preserved, at least at the transcriptional level. Stabilization during winter of mitochondrial structures, mRNAs, and ribosomes would reduce the cost of re-synthesis in spring and thus provide considerable energetic savings.