Isotopic discrimination between carrion and elytra clippings of lab-reared American burying beetles (Nicrophorus americanus): Implications for conservation and evaluation of feeding relationships in the wild.

Rationale Differences in stable isotope composition between an animal and its diet are quantified by experimentally derived diet-tissue discrimination factors. Appropriate discrimination factors between consumers and prey are essential for interpreting stable isotope patterns in ecological studies. While available for many taxa, these values are rarely estimated for organisms within the carrion food web. Methods We used a controlled-diet stable isotope feeding trial to quantify isotopic diet-tissue discrimination factors of carbon (delta C-13 values) and nitrogen (delta N-15 values) from laboratory-reared Nicrophorus americanus raised on carrion. We used exoskeleton samples of beetle elytra (wing covers) to determine diet-tissue discrimination factors using a continuous flow isotope ratio mass spectrometer equipped with an elemental analyzer. We also measured the isotopic compositions of five species of co-occurring, wild-caught burying beetles and evaluated feeding relationships. Results We found differences in stable carbon discrimination between carrion sources (mammalian and avian) and lab-reared beetles, but no difference in stable nitrogen discrimination. Values for delta C-13 did not differ among wild-caught burying beetle species, but values for delta N-15 were significantly different for the three species with overlapping breeding seasons. Furthermore, wild-caught burying beetles within our study area do not appear to use avian carrion resources to rear their young. Conclusions This study informs future interpretation of stable isotope data for insects within the carrion food web. In addition, these results provide insight into carrion resources used by co-occurring burying beetle species in situ. We also demonstrated that independent of adult food type, the larval food source has a significant impact on the isotopic signatures of adult beetles, which can be estimated using a minimally invasive elytra clipping.