Gas exchange and dive characteristics of the free-swimming backswimmer Anisops deanei

Abstract

Many aquatic insects utilise air bubbles on the surface of their bodies to supply O₂ while they dive. The bubbles can simply store O₂, as in the case of an 'air store', or they can act as a physical 'gas gill', extracting O₂ from the water. Backswimmers of the genus Anisops augment their air store with O₂ from haemoglobin cells located in the abdomen. The O₂ release from the haemoglobin helps stabilise bubble volume, enabling backswimmers to remain near neutrally buoyant for a period of the dive. It is generally assumed that the backswimmer air store does not act as a gas gill and that gas exchange with the water is negligible. This study combines measurements of dive characteristics under different exotic gases (N₂, He, SF₂, CO) with mathematical modelling, to show that the air store of the backswimmer Anisops deanei does exchange gases with the water. Our results indicate that approximately 20% of O₂ consumed during a dive is obtained directly from the water. Oxygen from the water complements that released from the haemoglobin, extending the period of near-neutral buoyancy and increasing dive duration.