Diet-tissue stable isotope (delta¹³C and delta¹⁵N) discrimination factors for multiple tissues from terrestrial reptiles (rock iguanas, Cyclura species)

Trophic interactions can drive community structure; therefore, studying food webs is key in understanding ecological communities. Stable isotope analysis is a powerful tool for reconstructing foraging patterns. However, stable isotope discrimination factors (delta¹³C and delta¹⁵N) are needed to best use this tool. We determined the first delta¹³C and delta¹⁵N values for Rock Iguanas (Cyclura spp.) to better understand isotope fractionation patterns in reptiles and estimate wild reptile diets. We analyzed delta¹³C and delta¹⁵N values between skin, blood, and scat from juvenile and adult iguanas held for over a year on a known diet and their food. We determined relationships between size/age and discrimination factors and compared isotope values from lipid- and non-lipid-extracted tissues and from scats that were treated/untreated with HCl. The delta¹³C and delta¹⁵N values ranged from -2.9 to +6.2⁰/₀₀ and from +1.7 to +7.0⁰ /₀₀, respectively, with some differences among tissues and between juveniles and adults. The delta¹³C values from blood and skin differed among species, but not delta¹⁵N values. The delta¹³C values from blood and skin and delta¹⁵N values from blood were positively correlated with size/age. The delta¹³C values from scat were negatively correlated with size (not age). Treatment with HCl (scat) and lipid extraction (skin) did not affect isotope values. Our results aid in the understanding of processes driving stable carbon and nitrogen isotope discrimination factors in reptiles. We provided estimates of delta¹³C and delta¹⁵N values and linear relationships between iguana size/age and discrimination factors for the best application of these values for interpreting wild reptile foraging ecology