title: Haemoglobin as a buoyancy regulator and oxygen supply in the backswimmer (Notonectidae, Anisops).
abstract: Unlike all other diving insects, backswimmers of the genus Anisops can exploit the pelagic zone by temporarily achieving near-neutral buoyancy during the course of a dive. They begin a dive positively buoyant due to the large volume of air carried in their ventral air-stores, but rapidly enter a protracted period of near-neutral buoyancy before becoming negatively buoyant. This dive profile is due to haemoglobin found in large tracheated cells in the abdomen. Fibre optic oxygen probes placed in the air-stores of submerged bugs revealed that oxygen partial pressure (P(O(2))) dropped in a sigmoid curve, where a linear decline preceded a plateau between 5.1 and 2.0 kPa, before a final drop. Buoyancy measurements made by attaching backswimmers to a sensitive electronic balance showed the same three phases. Inactivating the haemoglobin by fumigating backswimmers with 15% CO eliminated both buoyancy and P(O(2)) plateaus. Oxygen unloaded from the haemoglobin stabilises the air-store during the neutrally buoyant phase after a decrease in volume of between 16% and 19%. Using measurements of air-store P(O(2)) and volume, it was calculated that during a dive the haemoglobin and air-store contribute 0.25 and 0.26 microl of oxygen, respectively.
authors.affiliation: Ecology and Evolutionary Biology, School of Earth and Environmental Sciences, Darling Building, University of Adelaide, Adelaide, SA 5005, Australia. philip.matthews@adelaide.edu.au
authors.forename: Philip G D
authors.initials: PG
authors.lastname: Matthews
authors.forename: Roger S
authors.initials: RS
authors.lastname: Seymour
mesh_terms: D000388:Air / Q000032:analysis; D000818:Animals; D004242:Diving / Q000502:physiology; D006454:Hemoglobins / Q000502:physiology*; D007313:Insecta / Q000502:physiology*; D010100:Oxygen / Q000502:physiology*; D010313:Partial Pressure; D013550:Swimming / Q000502:physiology*; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D006454:Hemoglobins; D014867:Water; D010100:Oxygen