Oxygen and Carbon Isotope Variations in a Modern Rodent Community – Implications for Palaeoenvironmental Reconstructions

Abstract

BackgroundThe oxygen (δ18O) and carbon (δ13C) isotope compositions of bioapatite from skeletal remains of fossil mammals are well-established proxies for the reconstruction of palaeoenvironmental and palaeoclimatic conditions. Stable isotope studies of modern analogues are an important prerequisite for such reconstructions from fossil mammal remains. While numerous studies have investigated modern large- and medium-sized mammals, comparable studies are rare for small mammals. Due to their high abundance in terrestrial ecosystems, short life spans and small habitat size, small mammals are good recorders of local environments.Methodology/FindingsThe δ18O and δ13C values of teeth and bones of seven sympatric modern rodent species collected from owl pellets at a single locality were measured, and the inter-specific, intra-specific and intra-individual variations were evaluated. Minimum sample sizes to obtain reproducible population δ18O means within one standard deviation were determined. These parameters are comparable to existing data from large mammals. Additionally, the fractionation between coexisting carbonate (δ18OCO3) and phosphate (δ18OPO4) in rodent bioapatite was determined, and δ18O values were compared to existing calibration equations between the δ18O of rodent bioapatite and local surface water (δ18OLW). Specific calibration equations between δ18OPO4 and δ18OLW may be applicable on a taxonomic level higher than the species. However, a significant bias can occur when bone-based equations are applied to tooth-data and vice versa, which is due to differences in skeletal tissue formation times. δ13C values reflect the rodents’ diet and agree well with field observations of their nutritional behaviour.Conclusions/SignificanceRodents have a high potential for the reconstruction of palaeoenvironmental conditions by means of bioapatite δ18O and δ13C analysis. No significant disadvantages compared to larger mammals were observed. However, for refined palaeoenvironmental reconstructions a better understanding of stable isotope signatures in modern analogous communities and potential biases due to seasonality effects, population dynamics and tissue formation rates is necessary.

Chronology and ancient feeding ecology of two upper Pleistocene megamammals from the Brazilian Intertropical Region

“…Thus, the oxygen isotopic composition in mammalian tooth is influenced by the atmospheric O 2 , and water directly drunken from natural water bodies or present in their food, but only the latter two are highly variable and capable to explain the differences among taxa (Sponheimer and LeeeThorp, 2001 (Kohn et al, 1996;Helliker and Ehleringer, 2000). Nevertheless, some studies show that the d 18 O values of tooth apatite is a reflection of the isotopic composition of the meteoric and environmental water which megamammals were drinking, because large mammals (those with an obligatory drinking behavior) obtain most of the water by drinking rather than from their diets (Bryant and Froelich, 1995;Gehler et al, 2012). In the late Pleistocene of Southern Brazil, Lopes et al (2013) found a poor correlation between the d 18 O and d 13 C values for fossils of N.…”

Stable isotope relationships between apatite phosphate (δ18O), structural carbonate (δ18O, δ13C), and collagen (δ2H, δ13C, δ15N, δ34S) in modern human dentine

“…Furthermore, the results of several studies indicated that bioapatite δ 18 O carb values in enamel are higher than those of bone, whereas neither the enamel nor the bone δ 18 O phos values were consistently higher. Webb et al suggested that different fractionations of blood bicarbonate during bioapatite formation and maturation cause 18 O‐(and 13 C‐)enriched structural carbonate in enamel versus bone apatite, and Gehler et al explained this gap by different time intervals in the mineralization of the two tissues. Nevertheless, because the structure of dentine is more similar to that of bone than to enamel, we also expect lower δ 18 O carb values in dentine than in enamel.…”

Small mammal tooth enamel carbon isotope record of C4 grasses in late Neogene China

“…Yet micromammals are common in the fossil record and make up an important component of terrestrial ecosystems, and with their generally high fecundities, high local densities, and population growth rates, they hold tremendous potential as sensitive and quickly responding recorders of environmental changes. Other than size-imposed restrictions, micromammalian isotopic proxy records show no disadvantage compared to larger animals (Gehler et al, 2012) and have proven useful in a number of pioneering studies (e.g. Grimes et al, 2005;Hopley et al, 2006;Yeakel et al, 2007;Hynek et al, 2012;Kimura et al, 2013).…”