ABSTRACT
In this study we introduce the use of tunable diode laser absorption spectroscopy (TDLAS) as a technique for making measurements of the delta13C of animal 'breath' in near real time. The carbon isotope ratios (delta13C) of breath CO2 trace the carbon source of the materials being metabolized, which can provide insight into the use of specific food resources, e.g. those derived from plants using C3 versus C4 or CAM photosynthetic pathways. For physiological studies, labeled substrates and breath analyses provide direct evidence of specific physiological (e.g. fermentative digestion) or enzymatic (e.g. sucrase activity) processes. Although potentially very informative, this approach has rarely been taken in animal physiological or ecological research. In this study we quantify the utilization of different plant resources (photosynthetic types--C3 or C4) in arthropod herbivores by measuring the delta13C of their 'breath' and comparing it with bulk tissue values. We show that breath delta13C values are highly correlated with bulk tissues and for insect herbivores reflect their dietary guild, in our case C3-specialists, C4-specialists, or generalists. TDLAS has a number of advantages that will make it an important tool for physiologists, ecologists and behaviorists: it is non-invasive, fast, very sensitive, accurate, works on animals of a wide range of body sizes, per-sample costs are small, and it is potentially field-deployable.
