The Physiological Ecology of Larval Lestes disjunctus Selys (Zygoptera:Odonata)

Abstract

Lestes disjunctus is a common damselfly found in small, densely vegetated temporary ponds such as the Rocky Mountain 'bog pond' studied. Hatch occurs at ice melt in May, growth is rapid and emergence is in late July. Dissolved oxygen (DO) and temperature vary considerably during this time. During a 'typical' late July day temperature and DO may range from minima at dawn of 12°C and 3.1 ppm (lowest 1.8 ppm) to maxima at 1700 h of 22°C (highest 25.5°C) and 7.6 ppm. One mode of adaptation to such variable temperature conditions is low Q10. However, Lestes' Q10S (2.4-3.6) suggest that like most aquatic poikilotherms, it does not gain competitional advantage through unique thermal adaptation. Logic suggests that respiratory regulation would be a beneficial adaptation to variable DO. However, L. disjunctus is not a good regulator of respiration either. Oxygen intake decreases a temperature-dependent 15-27% from a normal environmental high DO to its low-O2 critical point. However, daytime DO variation only causes a 10% metabolic rate variation at 18.7°C (warm, sunny day). Most metabolic rate depression occurs at night due to lowering DO. Given Lestes' physiological abilities and the pond's environmental conditions, a relatively stable high metabolic rate and activity level result during the time larvae can see to feed (evidence suggests Lestes is a visual predator). At night, when larvae cannot see to feed, lowering DO reduces their metabolic rate and therefore activity, with the energy 'saved' from not regulating perhaps accounting for this species' rapid growth rate. Finally, O2 intake accounted for by large gills, and great tolerance of DO below its critical points, combine to allow survival for short periods when such low habitat DOs exist.