Oxygen consumption of the aquatic leaf beetles Macroplea mutica and Macroplea appendiculata is low and not influenced by salinity

Leaf beetles of the genus Macroplea live permanently under water. Species‐specific preferences for either freshwater or brackish water are available in the literature. To detect potential physiological differences, the oxygen consumption of Macroplea mutica and Macroplea appendiculata from habitats with differing salinities is measured at two different salinities (0 and 10). The specific oxygen consumption does not depend on oxygen saturation of the water (values in the approximate range of 25–100% occur during the experiments). There is no difference between species or sampling locations. Similarly, the salinity during the measurements does not affect the oxygen consumption of the beetles, either when compared as salinity per se (0 versus 10), or when classified as home salinity or atypical salinity. Comparisons with other chrysomelid beetles and aquatic insects (using available published data) reveal that the two Macroplea species have relatively low metabolic rates. This finding is discussed in the light of activity patterns and morphology, especially the reduction of flight muscles, which comprise a highly metabolically active tissue.