The responses of rectal pumping in some zygopteran larvae (Odonata) to oxygen and ion availability

Abstract

Rectal pumping movements have been observed to occur infrequently in larvae of the damselflies, Ischnura elegans and Enallagma cyathigerum, when kept in river water. However pumping became regular with a mean cycle duration of 6.8 ± 1.9 s (SE) after larvae were kept for 2–3 days in distilled water, whereas in 100 mM/l NaCl it usually ceased altogether. Oxygen lack caused larvae to perform short bursts of lateral abdominal wagging movements and then to approach the surface, but it had no effect on rectal pumping in these species. In contrast the frequency and amplitude of pumping in Calopteryx splendens were much increased by oxygen lack, though not by carbon dioxide excess, and pumping was also found to be responsive to the ion availability. By keeping larvae in solutions containing 0, 10, 100 and 200 mM NaCl/l, and making them hypoxic or hyperoxic, the responses to oxygen and ion levels in the medium were separately examined. The differences in the responsiveness of these species are discussed in terms of possible environmental adaptations.