PRI-TAL, B.*; BUNKELMANN, J.; DAVIDOWITZ, G.; GIBBS, A. G.; University of Arizona; Central Arizona College; University of Arizona; University of Nevada, Las Vegas: METABOLISM AND WATER BALANCE IN ARIZONA GRASSHOPPERS

We surveyed metabolic rates and water-loss rates of grasshoppers collected in southern Arizona. Across all individuals (>400 grasshoppers, representing >30 species and spanning 2 orders of magnitude in body size), metabolic rates scaled with an allometric exponent of 0.69. Similar scaling relationships occurred within species. Approximately 20% of grasshoppers exhibited discontinuous gas-exchange cycles (DGC), and another 20% released CO₂ in a cyclic or �inter-burst� pattern. These patterns were not associated with lower water-loss rates; for example, Xanthippus corallipes consistently exhibited DGC but lost water relatively rapidly. The scaling exponent for total water-loss rate, across species, was 0.76. Cuticular transpiration (CWL, calculated by a regression technique, scaling exponent = 0.74) accounted for ~85% of total water loss. After correction for size, CWL was not correlated with the melting point of cuticular lipids. However, CWL was correlated with metabolic rate and total water-loss rate (analyses of residuals, P < 0.001). We conclude that variation in overall water loss reflects differences in both respiratory and cuticular water loss, that DGCs do not significantly reduce total water-loss rates, and that differences in cuticular permeability do not result from differences in surface lipid properties. Supported by NSF award IOB-0514402 to AGG.