Nitrogen stable isotope turnover and discrimination in lizards

Abstract

Rationale Nitrogen stable isotope ratio (δ15N) processes are not well described in reptiles, which limits reliable inference of trophic and nutrient dynamics. In this study we detailed δ15N turnover and discrimination (Δ15N) in diverse tissues of two lizard species, and compared these results with previously published carbon data (δ13C) to inform estimates of reptilian foraging ecology and nutrient physiology. Methods We quantified 15N incorporation and discrimination dynamics over 360 days in blood fractions, skin, muscle, and liver of Sceloporus undulatus and Crotaphytus collaris that differed in body mass. Tissue samples were analyzed on a continuous flow isotope ratio mass spectrometer. Results Δ15N for plasma and red blood cells (RBCs) ranged between +2.7 and +3.5‰; however, skin, muscle, and liver did not equilibrate, hindering estimates for these somatic tissues. 15N turnover in plasma and RBCs ranged from 20.7 ± 4 to 303 ± 166 days among both species. Comparison with previously published δ13C results for these same samples showed that 15N and 13C incorporation patterns were uncoupled, especially during winter when hibernation physiology could have played a role. Conclusions Our results provide estimates of 15N turnover rates and discrimination values that are essential to using and interpreting isotopes in studies of diet reconstruction, nutrient allocation, and trophic characterization in reptiles. These results also suggest that somatic tissues can be unreliable, while life history shifts in nutrient routing and metabolism potentially cause 15N and 13C dynamics to be decoupled.

Inter- and intrapopulation resource use variation of marine subsidized western fence lizards

“…A comparable Δ 15 Ntissue-diet value for lizard skin was not published since the tissue did not reach equilibrium by the end of the 360 day study (Warne & Wolf, 2021). These studies highlight the relatively slow carbon and nitrogen incorporation rates measured in terrestrial ectotherm tissues, and suggest that our samples likely represent an average diet over months (Warne et al, 2010;Warne & Wolf, 2021).…”

“…Since the tail tip samples were a composite by biomass of primarily scale (keratin), skin, and connective tissue we relied on Δ 13 Ctissue-diet and Δ 15 Ntissue-diet values calculated for lizard claw keratin (+1.2 ± 0.4‰ , and +0.7 ± 0.3‰, respectively) (Lattanzio & Miles, 2016), and a Δ 13 Ctissue-diet value for lizard skin (-0.8 ± 0.5‰) (Warne et al, 2010). A comparable Δ 15 Ntissue-diet value for lizard skin was not published since the tissue did not reach equilibrium by the end of the 360 day study (Warne & Wolf, 2021). These studies highlight the relatively slow carbon and nitrogen incorporation rates measured in terrestrial ectotherm tissues, and suggest that our samples likely represent an average diet over months (Warne et al, 2010;Warne & Wolf, 2021).…”

“…Stable isotope analyses (SIA) are routinely used to investigate how resource subsidies link adjacent habitats and environments (Bartels et al, 2012;Pringle & Fox-Dobbs, 2008). Carbon and nitrogen in consumer tissues are derived from diet, and therefore the isotopic composition (reported as δ 13 C and δ 15 N values) of predators such as lizards reflect the values of their prey (Boecklen et al, 2011;Peterson & Fry, 1987;Warne et al, 2010;Warne & Wolf, 2021). The substantial and predictable differences in marine versus terrestrial food web δ 13 C and δ 15 N values means that SIA has been widely used for decades to make robust estimates of the relative contributions of diet sources from each environment for coastal consumers (Hobson & Sealy, 1991).…”

Inter- and intrapopulation resource use variation of marine subsidized western fence lizards

“…Stable isotope analyses (SIA) are routinely used to investigate how resource subsidies link adjacent habitats and environments (Bartels et al 2012 ; Pringle and Fox-Dobbs 2008 ). Carbon and nitrogen in consumer tissues are derived from diet, and therefore the isotopic composition (reported as δ 13 C and δ 15 N values) of predators such as lizards reflect the values of their prey (Boecklen et al 2011 ; Peterson and Fry 1987 ; Warne et al 2010 ; Warne and Wolf 2021 ). The substantial and predictable differences in marine versus terrestrial food web δ 13 C and δ 15 N values mean that SIA has been widely used for decades to make robust estimates of the relative contributions of diet sources from each environment for coastal consumers (Hobson and Sealy 1991 ).…”

Intra-Body Variations of Stable Isotope Ratios (δ13C, δ15N) and Influence of Storage Methods in Aquatic and Post-Aquatic Stages of the Common Toad, Bufo bufo

“…These differences determine the variation in the isotopic composition of various tissues and organs [14,17]. Indeed, a significant variation in the isotopic composition of carbon (δ 13 C) and nitrogen (δ 15 N) within one organism was shown for a number of invertebrates and vertebrates, including diplopods [18], orthopterans [19], aphids [20], fishes [21], reptiles [22,23], birds [24] and mammals [25][26][27]. However, we know little about such differences between tissues in amphibian [28][29][30], which play an important role in trophic webs of both aquatic (in larval stage) and terrestrial (as adults) ecosystems.…”