Abstract
Many stable isotope analysis (SIA) stud- ies aim to track protein, which is assimilated in animal tissues from their food sources, to assess feeding ecol- ogy, movements, and ontogenetic shifts of marine ani- mals. Lipids are known to be a potential source of bias because they are depleted in 13 C compared to 12 C. Al- though lipids are usually removed before SIA, there is a lack of standardized analytical protocols for this pro- cedure. We tested the effects of lipid extraction with 2 chemical solvents (chloroform-methanol and petro- leum ether) in the humeri of the loggerhead sea turtle Caretta caretta to establish a standard protocol for processing the bone collagen of marine animals and to develop a mathematical cor rection. In both lipid ex- traction treatments, δ 13 C values were higher than the control, but only lipid extraction with chloroform- methanol showed significant differences. By contrast, the δ 15 N values were not affected by lipid extraction treatments with either solvent. The linear regression between the C:Nbulk ratio and Δ 13 C was not significant, which does not support the assumption that there is a predictable relationship between the C:N ratio and lipid content. Nevertheless, a significant positive rela- tionship be tween Δ 13 C and δ 13 Cbulk was observed, but such a model is not recommended as a mathematical lipid correction method because the model efficiency had a negative value, which indicates that the mean value of δ 13 Cle is a better predictor than the model it- self. These results suggest that lipid extraction should be taken into account in SIA of bone collagen tissues for accurate δ 13 C determination.
Highlights
Over the past several decades, stable isotope analysis (SIA) has become a useful tool in ecological research, for identifying dietary sources and trophic relationships (e.g. Godley et al 1998, Dodge et al 2011), habitat use (Bjorndal & Bolten 2010, Pajuelo et al 2012), migration patterns (Hobson 1999), and ontogenetic shifts (Arthur et al 2008, Drago et al 2009)
The carapace length (CCL) of the 11 sampled turtles ranged from 50.0 to 93.0 cm, representing juveniles and adults based on the size range of mature loggerhead sea turtles from Brazilian nesting areas in Espírito Santo state (83.0 to 120.0 cm CCL; Baptistotte et al 2003) and Rio de Janeiro (86.5 to 114.5 cm; Lima et al 2012)
In both lipid extraction treatments, mean δ13C values were higher than the control (Table 1)
Summary
Over the past several decades, stable isotope analysis (SIA) has become a useful tool in ecological research, for identifying dietary sources and trophic relationships (e.g. Godley et al 1998, Dodge et al 2011), habitat use (Bjorndal & Bolten 2010, Pajuelo et al 2012), migration patterns (Hobson 1999), and ontogenetic shifts (Arthur et al 2008, Drago et al 2009). Over the past several decades, stable isotope analysis (SIA) has become a useful tool in ecological research, for identifying dietary sources and trophic relationships SIA is a well-suited method for such studies because the stable isotope values of carbon (δ13C) and nitrogen (δ15N) reflect a timeintegrated diet, i.e. the stable isotope ratio of con-. Kinetic effects that occur during the conversion of pyruvate to acetyl CoA cause a depletion in carbon stable isotope ratios of approximately 6 to 8 ‰ (DeNiro & Epstein 1977). Lipid-corrected δ13C values more accurately reflect the carbon assimilated by consumers and provide more clear information about the magnitude of fractionation from prey to predators and relationships between them (D’Ambra et al 2014)
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