Hydrogen Isotopes in Beetle Chitin

Beetles, one of the most diverse and long-lived animal groups, provide a trove of ecological and palaeoenvironmental information largely because their exoskeletons contain chitin, a highly resistant biopolymer which preserves well in the geological record. In addition to palaeoenvironmental inferences that can be derived from presence or absence of particular taxa, beetle chitin records the hydrogen stable isotope ratios (D/H) of environmental water, which is related to temperature and other environmental variables. Because the vast majority of beetle fossils consists of incomplete body parts, the H isotopic variability within and between beetle specimens must be quantified. We provide data that show intra- and inter-specimen D/H variation in modern water beetles that may relate to systematic variations in chitin biosynthesis during exoskeleton development. A discussion of existing hydrogen-isotope studies of chitin are presented, including recent advances in hydrogen-isotope analysis that can enhance sample throughput.