Respiratory Roles of Caudal lamellae (Gills) in a Lestid Damselfly (Odonata:Zygoptera)

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Abstract
The three caudal lamellae of zygopterous Odonata are often considered to be gills, but this viewpoint is not universally held. Because the genus Lestes possesses the largest proportionate gill size amongst Zygoptera, I selected a member of this genus for the purpose of answering the question: are caudal lamellae actually gills? Large numbers of gilled and gill-less larvae were used in low-O2 survival and closed-bottle respirometry experiments. When gill removal was necessary, ablation was accomplished only by autotomy. Results demonstrate that caudal lamellae of the lestid damselfly, Lestes disjunctus Selys, can function as gills whatever their other roles. The three lamellae meet all gill criteria: they are large and thin, possess little metabolizing bulk, and are moist, vascular and sometimes ventilated. Lamellae are normally responsible for 20-30% of O2 intake. As the dissolved O2 concentration (DO) falls and temperature rises, gills account for more and more O2 intake and do so up to their proportion of total body surface area (∼70%). With sufficient DO and at low temperatures (2 intake well due to their mediocre ventilatory mechanism ("pull-downs"), nor do gills affect larval ability to regulate O2 intake. Another effect of weak ventilation is that low-O2 critical points are rather high (2.5-5.5 mg/L at ∼12-25°C). The importance of gills in obtaining DO is further demonstrated by the positive correlation between survival at low DO concentrations and the amount of gill surface area present (0, 1, 2 or 3 gills). With any given amount of gill surface, larvae die at increasingly higher DO concentrations as temperatures rise. At any given temperature the reduction of gill surface results in more DO being required for survival.

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