The effects of overwintering stresses (low temperature, low oxygen concentration) on the life history patterns of activity-specific oxygen consumption by Nephelopsis obscura were determined using a flow-through respirometer system and compared with leeches hatched and maintained under summer conditions. While resting and active oxygen consumption increased with body dry weight, weight-specific resting (Rm) and active (Ra) oxygen consumption and aerobic scope (AS) decreased with increase in body weight in both winter and summer N. obscura. Rm in winter leeches was higher than in summer leeches, probably reflecting the higher metabolic costs of tissue repair and maintenance after winter stresses. Although Ra and AS in winter leeches were initially lower than in summer leeches, by stage 4, compensation in winter leeches was complete and by stage 6, over-compensation occurred. The effects of overwintering on oxygen consumption and AS persisted throughout the life history and help explain some of the differences in allocation of energy storage observed in winter and summer leeches.
