Gas exchange and dive behaviour in the diving beetle Platynectes decempunctatus (Coleoptera: Dytiscidae)

Many aquatic insects use bubbles on the body surface to store and supply O₂ for their dives. There are two types of bubbles: air stores, which store O₂ gained from air at the surface, and gas gills that allow passive extraction of O₂ from water. Many insects using air stores and gas gills return to the surface to replenish their bubbles and, therefore, their requirement for O₂ influences dive behaviour. In this study, we investigate gas exchange and dive behaviour in the diving beetle Platynectes decempunctatus that uses a sub-elytral air store and a small compressible gas gill. We measure the PO₂ within the air store during tethered dives, as well as the amount of O₂ exchanged during surfacing events. Buoyancy experiments monitor the volume of gas in the gas gill and how it changes during dives. We also directly link O₂-consumption rate at three temperatures (10, 15 and 20 °C) with dive duration, surfacing frequency and movement activity. These data are incorporated in a gas exchange model, which shows that the small gas gill of P. decempunctatus contributes less than 10% of the total O₂ used during the dive, while up to 10% is supplied by cutaneous uptake.