Assimilation and isotopic discrimination of hydrogen in tilapia: implications for studying animal diet with δ²H

Abstract

Abstract. Hydrogen isotope (d 2Η) analysis has become a valuable tool in the study of animal migration; however, the biochemical framework required for ecologists to confidently apply d 2 Η to quantify resourceuse has yet to be adequately resolved. sources? We completed a 3 9 3 controlled feeding experiment on Nile tilapia (Oreochromis niloticus) in which we varied the d 2 Η of tank water and dietary macromolecules to examine these questions in two tissues commonly analyzed by ecologists: muscle and liver. We found that the proportion of hydrogen in tilapia tissue derived from tank water was similar for muscle (~23%) and liver (~25%). We then used linear regression and an isotope mixing model based on accompanying d 13 C data to estimate the proportion of hydrogen in muscle and liver tissue derived from dietary protein (34-44%), cornmeal (21-27%), corn syrup (4-5%), and lipids (≤1%). With this information and the d 2 Η values of water, protein, carbohydrates, and lipids supplied to fish in each treatment, we calculated D 2 H net values of À47& AE 5& for muscle and À41& AE 5& for liver. Our experiment is the first to quantify the relative proportion of hydrogen from different dietary macromolecules used by an omnivore to synthesize its tissues. Such information is needed to further refine the use of d 2 Η analysis as a dietary tracer for aquatic animals.

An assessment of assumptions and uncertainty in deuterium‐based estimates of terrestrial subsidies to aquatic consumers

“…, Hondula and Pace , Newsome et al. ) have found higher values (i.e., ω = 0.32 ± 0.10, n = 7) than Solomon et al. () initially reported for controlled feeding experiments (i.e., ω = 0.21 ± 0.11, n = 5).…”

“…Much more information is needed regarding the physiological processes that cause variation in ω in order to effectively use 2 H/ 1 H analyses to infer consumer diets (Newsome et al. ).…”

“…Despite this uncertainty in ω, there has been little effort to determine the most appropriate values for use in trophic studies where consumer 2 H/ 1 H is used to infer diet composition or basal energy source, and the sensitivity of mixing models estimates to this parameter (Newsome et al. ).…”

Fruit of the forest ‐ larval sea lamprey Petromyzon marinus are fuelled by allochthonous resources

“…While the fractionation values of carbon and nitrogen in aquatic food webs are well known (Post, ), albeit with some variation (Vander Zanden & Rasmussen, ), there is considerably greater uncertainty regarding the trophic fractionation of hydrogen (Soto et al, ). Many studies focussed on aquatic food webs assume fraction in δ 2 H to be negligible (Doucett et al, ; Solomon et al, ) while others have detailed fractionation values ranging between 20‰ (Birchall et al, ) and −40‰ (Newsome et al, ) per trophic level. The consumers analysed here were not enriched in δ 2 H relative to the primary producers and there was no discernible correlation between δ 2 H and δ 15 N across the dataset.…”

Terrestrial contributions to Afrotropical aquatic food webs: The Congo River case

“…Stable hydrogen isotope ratios (δ 2 H) have recently gained attention to complement "traditional" isotopes for aquatic food webs due to their potentially greater power to separate sources (Cole et al, 2011;Jardine, Kidd, & Cunjak, 2009;Newsome, Wolf, Bradley, & Fogel, 2017;Soto, Wassenaar, & Hobson, 2013). Their utility in the study of terrestrial versus aquatic sources contributions in aquatic food webs is based on the fact that δ 2 H values are generally much lower in aquatic producers compared to terrestrial inputs such as leaf litter (Doucett, Marks, Blinn, Caron, & Hungate, 2007).…”