Assimilation and discrimination of hydrogen isotopes in a terrestrial mammal

Abstract

Stable isotope analysis has revolutionized the way ecologists study animal resource use from the individual to the community level. Recent interest has emerged in using hydrogen isotopes (H/H) as ecological tracers, because they integrate information from both abiotic and biotic processes. A better physiological understanding of how animals assimilate hydrogen and use it to synthesize tissues is needed to further refine this tool and broaden its use in animal ecology. We conducted a controlled-feeding experiment using laboratory mice (Mus musculus) in which we varied the hydrogen isotope (δH) values of water and the proportions of dietary protein and carbohydrates among nine experimental treatments. For each tissue, we calculated the percent of hydrogen derived from water and the percent hydrogen derived from dietary protein versus carbohydrates using linear relationships and isotope mixing models based on accompanying carbon isotope (δC) data. The net discrimination (∆H) between mice tissues and potential water and dietary sources of hydrogen differed among tissues. ∆H was positively correlated with dietary protein content in red blood cells (RBC) and muscle, but negatively correlated in liver and plasma. We also report the first estimates for hydrogen isotope discrimination factors (∆H) for different sources of hydrogen (∆H, ∆H, and ∆H) available for tissue synthesis. This research provides a foundation for understanding how diet quality (e.g., protein content) influences hydrogen isotope assimilation and discrimination in different tissues of a terrestrial mammal, which is a first step towards using δH as a tracer of resource use in free-ranging mammals.

Physiology Drives Reworking of Amino Acid δ2H and δ13C in Butterfly Tissues

“…Essential Amino Acid δ 2 H AA Ess δ 2 H data further show that the hydrogen isotope composition of individual amino acids is systematically modified according to the biochemical pathways used for synthesis and that eukaryotes and many prokaryotes utilize the same basic metabolic machinery to do so (Rodriguez Curras et al, 2018;Newsome et al, 2020). As was the case with E. coli (Fogel et al, 2016) and house mice (Newsome et al, 2020) reared in controlled feeding experiments, Ile has the lowest δ 2 H values of all amino acids in our dataset.…”

“…For this reason, and because hydrogen in a molecule has many opportunities to exchange with other pools of hydrogen during metabolic reactions, hydrogen cycling is more complex than that of more conventional biomarkers such as carbon or nitrogen isotopes. In fact, nearly all the research into the biochemical processes that govern incorporation of δ 2 H into consumer tissues stems from controlled feeding experiments in the lab (Estep and Dabrowski, 1980;Peters et al, 2012;Fogel et al, 2016;Newsome et al, 2017;Rodriguez Curras et al, 2018), with relatively little being done in natural ecosystems across trophic levels. Establishing a biochemical framework for the propagation of δ 2 H through food webs would expand our ability to resolve smaller regional-scale animal movements and potentially unlock new applications for δ 2 H data in dietary and metabolic studies.…”

Dietary protein content and digestibility influences discrimination of amino acid nitrogen isotope values in a terrestrial omnivorous mammal

“…The results reported here for Experiment A represent additional analyses of samples first described in Rodriguez Curras et al 19 Specifically, 34 mice (each offered 10 g food day −1 ) were divided into three diet treatments that varied in casein content: A‐L for low protein, A‐I for intermediate protein, and A‐H for high protein (Table 1). The protein categories were based on the recommended protein content of ~0.20 by mass for mice 17 .…”

“…For Experiments A and B, muscle was lipid‐extracted by soaking samples for 72 h in a 2:1 chloroform/methanol solution, replacing the solvent solution every 24 h 4,19 . Samples were then rinsed thoroughly with deionized water and freeze‐dried.…”

Hydrogen isotope assimilation and discrimination in green turtles

“…trophic discrimination factors, Δ 2 H Net ). In regard to the first challenge, controlled feeding experiments show that the majority (∼70-80%) of hydrogen in consumer tissues is derived from diet, whereas only ∼20-30% is sourced from environmental or drinking water (Rodriguez Curras et al, 2018;Newsome et al, 2017;Solomon et al, 2009;Wolf et al, 2011). Fewer studies have focused on quantifying Δ 2 H Net , which is mediated by physiological processes during resource assimilation, tissue synthesis and excretion.…”