Respiratory Regulation in Ephemera Simulans Walker and Hexagenia Limbata (Serville) (Ephemeroptera)

Abstract

ABSTRACT This study shows that Ephemera simulans and Hexagenia limbata are respiratory regulators and how it is that regulation is attained and maintained. Nymphs, 17-24 mm. in length, were acclimated in the laboratory at 13·0° C. for 24 hr. Oxygen consumption experiments employed the ‘closed-bottle’ technique and several modifications. When studied in bottles containing no substrate, both species appeared to be respiratory adjustors. Using ‘optimal substrates’ and a wide range of oxygen concentrations, both species proved to be respiratory regulators. As the oxygen concentration decreased, respiratory regulation was attained by initiating and increasing a flow of water past the body surfaces by the bailer action of beating gills. The volume passed was proportional to the number of gill beats which, in turn, was influenced by the size of the gills. The larger gills of Hexagenia beat at a slower rate to produce the same current as Ephemera and potentially they were capable of producing a significantly greater current and, hence, could regulate to a lower oxygen concentration.