Studies on gas exchange in the meadow spittlebug, Philaenus spumarius: the metabolic cost of feeding on, and living in, xylem sap.

Spittlebugs (superfamily Cercopoidea) live within a mass of frothy, spittle-like foam that is produced as a by-product of their xylem-feeding habits. The wet spittle represents a unique respiratory environment for an insect, potentially acting either as a reserve of trapped oxygen (O2) or as a significant barrier to O2 diffusion from the surrounding atmosphere. Feeding on xylem sap under tension is also assumed to be energetically expensive, potentially placing further constraints on their gas exchange. To understand the respiratory strategies used by spittlebugs, this study measured the PO2  within the spittle of the meadow spittlebug, Philaenus spumarius, as well as the non-feeding metabolic rate (RMR) and respiratory quotient (RQ) of both nymphs and adults. The metabolic rate of nymphs feeding on xylem was also measured. In separate experiments, the ability of a nymph to obtain O2 from bubbles while submerged in foam was determined using a glass microscope slide coated in an O2-sensitive fluorophore. We determined that P. spumarius breathes atmospheric O2 by extending the tip of its abdomen outside of its spittle, rather than respiring the O2 trapped in air bubbles within the foam. However, spittlebugs can temporarily use these air bubbles to breathe when forcibly submerged. V̇O2  and V̇CO2  did not differ statistically within life stages, giving a RQ of 0.92 for nymphs and 0.95 for adults. Feeding on xylem was found to increase the nymphs' V̇CO2  by only 20% above their RMR. From this cost of feeding, cibarial pump pressures were estimated to be between -0.05 and -0.26 MPa.

Cerium oxide nanoparticles exhibit minimal cardiac and cytotoxicity in the freshwater fish Catostomus commersonii.

Metal oxide nanomaterials can cause oxidative, cardiorespiratory, and osmoregulatory stress in freshwater fish. In contrast, cerium oxide nanoparticles (nCeO2) can have antioxidant effects but their aquatic toxicity has not been fully characterized. Heart rate and heart rate variability were followed in white sucker (Catostomus commersonii) acutely exposed to 1.0 mg L(-1) nCeO2 for 25 h. Malondialdehyde (MDA) was measured to assess oxidative tissue damage, and plasma cortisol, glucose, lactate, and osmolality were assessed as indicators of physiological and osmoregulatory stress. There was no MDA accumulation in gill or heart of fish exposed to nCeO2 and heart function was unchanged over the 25 h treatment. Plasma cortisol increased 6-fold but there was no change in plasma glucose or lactate. Cellular osmoregulatory toxicity was studied using an isolated red blood cell (RBC) model. In vitro exposure to 1.0 mg L(-1) nCeO2 for 1h had no effect on cell morphological parameters and did not sensitize RBCs to hemolysis under hypotonic stress. Overall, there were no indications of oxidative, cardiorespiratory, or osmoregulatory stress following acute exposure to nCeO2. Elevated plasma cortisol levels suggest that nCeO2 may exert mild toxicity to tissues outside of the cardiorespiratory system.