CHITIN AND BODY WATER ISOTOPIC COMPOSITION IN GRASSHOPPER SPECIES OF NORTHERN COLORADO
Four species of grasshopper were collected during summer 2012 from five sites near Boulder, CO, ranging in elevation from 1575 m to 3500 m. Chitin samples were cut from grasshopper wing and leg segments and were equilibrated with laboratory atmosphere to normalize exchangeable hydrogen compositions prior to analysis with TCEA-IRMS. Body water was distilled from frozen specimens using a vacuum extraction line and water samples were analyzed for δD and δ18O (LGR Liquid Water Isotope Analyzer).
Measured grasshopper chitin and body water isotopic compositions were both highly variable. Chitin δD values ranged from -134‰ to -54‰(VSMOW), and δ18O from +22‰ to +46‰ (VSMOW), while body water δD values ranged from -54‰ to +109‰ and δ18O from +5‰ to +25‰. Much of this variation is attributable to differences among species. Female specimens exhibited broader ranges in both chitin and body water isotopic compositions, with more depleted average values than males. Discrepancies between male and female isotopic compositions may reflect physiological differences related to oviposition. Preliminary data suggest isotopic enrichment in grasshopper chitin at higher elevations, consistent with decreasing humidity in the arid subalpine environment. Relationships between elevation and body water isotopic composition reflect altitude and humidity gradients in meteoric water compositions but are complicated by behavioral differences among species.