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

Abstract

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 (δ 13 C values) and nitrogen (δ 15 N 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 δ 13 C did not differ among wild-caught burying beetle species, but values for δ 15 N 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.

Stable isotope ecology in insects: a review

“…elytra notches; Fig. 3) are less invasive (Quinby et al ., 2020). Further studies evaluating routing, assimilation, species‐specific discrimination factors, and CSIA provide opportunities for entomologists to add to the field of stable isotope ecology while at the same time gain insight to previously unanswered questions.…”

“…3. Example of a minimally invasive elytral notch used to determine stable isotope signatures (δ 13 C and δ 15 N) in the Federally Endangered American burying beetle (Nicrophorus americanus; Quinby et al, 2020). (Gannes et al, 1997;Wolf et al, 2009).…”

“…Studies determined δ 2 H signatures of keratin in wings of monarch butterflies (Danaus plexippus) indicated natal origins when combined with keratin δ 13 C signatures (which shows a general pattern of enrichment along a southeast to northeast gradient) in their wings (Wassenaar & Hobson, 1998;Hobson et al, 1999;Flockhart et al, 2017). Doucett et al (2007) estimated energy flow partitioning in aquatic ecosystems by evaluating contributions of aquatic and terrestrial sources of δ 2 H to et al, 1979;Akamatsu et al, 2004;Feldhaar et al, 2010Adams et al, 2016 Blüthgen et al, 2003;Feldhaar et al, 2010;Doucett et al, 2007 Scrimgeour et al, 1995;Ostrom et al, 1996;Tayasu, 1998;McCutchan et al, 2003;Spence & Rosenheim, 2005;Haubert et al, 2005Caut et al, 2009Feldhaar et al, 2010Semenina & Tiunov, 2011Brauns et al, 2018;Matos et al, 2018;Quinby et al, & Hobson, 1998;Hobson et al, 1999;Heinrich et al, 2012;Hobson et al, 2012;Holder et al, 2014Flockhart et al, 2017 Tayasu, 1998;Nardi et al, 2002;Fischer et al, 2003 aquatic insects and fish using SIMMs. Stable isotopes of oxygen and carbon were used to identify spruce budworm (Choristoneura fumiferana) outbreaks in a boreal forest of northeastern North America (Simard et al, 2008).…”

“…Many studies document considerable variation in discrimination factors (Hobson et al ., 1996; Hobson & Cherel, 2006; Franssen et al ., 2017) and SIMMs are sensitive to differences in discrimination factors (Post, 2002; Phillips et al ., 2014). Entomologists can explore feeding relationships in systems where a direct observation or traditional methods are not feasible (Hood‐Nowotny & Knols, 2007; Hyodo, 2015; Quinby et al ., 2020), and explore complex ecological interactions spanning multiple levels of organisation (Ben‐David & Flaherty, 2012). Stable isotopes allow researchers to evaluate the response of individuals to environmental conditions (Norris et al ., 2007), evaluate the potential importance of gut symbionts for insect nutrition (Hyodo 2015), detect biosynthetic pathways based on labelled compounds (Chamberlain et al ., 2004), gain complementary dietary information from other chemical signatures (e.g.…”

“…exoskeleton) reflect dietary intake over longer periods (e.g. months or specific life stages; Gratton & Forbes, 2006; Quinby et al ., 2020) and remain understudied.…”