The functional morphology of caudal lamellae in coenagrionid (Odonata:Zygoptera) damselfly larvae

Abstract During their later instars, coenagrionid damselfly larvae reduce their relative investment in lamellae. Caudal lamellae play a role in swimming by allowing a larva to take advantage of its body size when at least one lamella is present, and this benefit increases with larval size. The removal of the first and/or second lamella generally results in a fixed and measurable decrease in swimming speed. When all lamellae are removed, larvae suffer a dramatic reduction in swimming speed. Ischnura posita (Hagen) and Enallagma civile (Hagen) always swim faster than equal sized Telebasis salva (Hagen) and Argia translata (Hagen) when at least one lamella is present. The swimming speed of the three lentic forms I. posita, E. civile, and T. salva is more affected by lamella loss than the lotic form A. translata. These last three relationships do not change ontogenetically. Caudal lamellae surface area does not increase as fast ontogenetically as would be expected for a gas exchange organ. The breaking joints, which hold the lamellae to the body, do not grow isometrically with body size, but do grow isometrically with lamellar mass. This suggests that the lamellae may be retained in proportion to investment (mass).