Meeting Abstract

34.5  Wednesday, Jan. 5  Lost Gills and Low Oxygen: Respiratory Ecology of Damselfly Larvae SESTERHENN, T.M.*; REARDON, E.E.; CHAPMAN, L.J.; Univ. of Kentucky, Lexington; McGill Univ., Montreal, PQ; McGill Univ., Montreal, PQ iposita@gmail.com

Oxygen limitation is an important influence on the ecology of aquatic animals. The respiratory ecology of larval damselflies is of particular interest because of their caudal lamellae (external gills), and often individuals are missing at least one lamella. We tested the hypothesis that missing lamellae would impact the respiratory ecology of the damselfly Ischnura posita by lowering metabolic rates and increasing ventilation behaviors. We measured the metabolic rates of one set of damselflies using closed respirometry, which also yielded critical oxygen tensions – the level of DO below which individuals cannot maintain their metabolic rate. Another set of damselflies was exposed to four levels of DO and their ventilation behaviors, activity, and time spent at the surface (to access atmospheric air) were measured. Critical tension was affected by mass, with larger individuals able to maintain their metabolic rate to lower DO; however, lamella number did not affect metabolic rate or critical tension. In behavioral trials, smaller animals and individuals missing lamellae spent more time at the surface at the lowest level of oxygen. Ventilation behaviors and activity were not affected by lamella number, but both increased at low levels of DO. I. posita is well-adapted to low-oxygen environments; critical tensions were extremely low compared to other freshwater invertebrates and fishes, and ventilation behaviors changed only at low levels of DO. Although lamella number was not an important factor in respiration, individuals with missing lamellae did spend more time at the surface which could increase predation risk. The ability to function well in low-oxygen environments could confer a competitive advantage to I. posita and facilitate its large range.