The prospects of poop: a review of past achievements and future possibilities in faecal isotope analysis

Is What Comes out the Same as What Goes in? A Preliminary Investigation of the Isotopic Impacts of Digestion by Red-Tailed Hawks (Buteo jamaicensis) and Eurasian Eagle Owls (Bubo bubo)

We investigated isotopic diet-excreta offset (Δdiet-excreta) for predatory birds, and the isotopic influence of bird digestion on consumed prey tissues. Foraging ecology of predatory birds can be non-invasively monitored using excreta or regurgitated prey. However, one must account for Δdiet-excreta and any influence of digestion on prey tissues. Neither of these has been previously evaluated for predatory birds. We worked with a captive Eurasian eagle owl (Bubo bubo) and red-tailed hawk (Buteo jamaicensis) fed frozen murid rats. We collected rat feet, as well as regurgitated pellets and excreta from each bird's enclosure. We analyzed carbon (δ13C) and nitrogen (δ15N) isotopes in undigested rat muscle, undigested and digested fur, and bone collagen (extracted from pellets), δ13C, oxygen (δ18O), and strontium (87Sr/86Sr) isotopes in rat bone bioapatite, and δ13C, δ15N, and 87Sr/86Sr in bird excreta. Diet-excreta offset differed slightly between individuals and depended on how we estimated diet (muscle alone or muscle + collagen) and if excreta were acidified. We tentatively suggest using +1 to 1.5‰ for Δ13Cdiet-excreta and +0.5 to 1‰ for Δ15Ndiet-excreta when working with proteinaceous tissues and unacidified or acidified excreta, respectively. For bioapatite, we suggest +9 to 10‰ for Δ13Cdiet-excreta and +0.001 for 87Sr/86Srdiet-excreta. Fur isotopes, collagen δ15N, and bioapatite δ18O were unaffected by digestion, but 87Sr/86Sr decreased by 0.0005 to 0.001, and collagen and bioapatite δ13C shifted 0.5 to 1‰ (decreasing collagen-apatite spacing by 1.5 to 2‰). For both birds, Δdiet-excreta for carbon and strontium were similar to previous studies, but nitrogen was notably different, possibly because excreta contained some urine or urates, or because raptors have distinct digestive physiologies. The influence of digestion on bone δ13C and 87Sr/86Sr is large enough to affect interpretations of diet and bioavailable strontium. Researchers should use caution if relying on potentially digested bone to evaluate the diet of consumed prey, establish strontium baselines, or infer past climate or environmental conditions.

Symbiotic Relationship of Comasterschlegelii (Crinoidea: Comatulidae) and Gymnolophus obscura (Ophiuroidea: Ophiotrichidae) Derived from Stable Isotope and Fatty Acid Analyses

Coral reef community exhibits high species diversity and a broad range of biological relationships, including widespread symbiosis and complex food utilization patterns. In our study, we investigated the symbiotic relationship between the commonly crinoid host Comaster schlegelii and its ophiuroid obligatory symbiont Gymnolophus obscura. Using a combination of fatty acid biomarkers and stable isotopic compositions, we explored differences in their organic matter utilization strategies and nutritional relationships. The result of stable isotopes revealed that G. obscura had higher δ15N values than its crinoid host. Particulate organic matter and phytoplankton were identified as the primary food sources for both species, however C. schlegelii showed a higher proportional contribution from benthic microalgae. Fatty acid markers showed that C. schlegelii was more dependent on benthic microalgae such as diatoms, and less on debritic organic matter and bacteria than G. obscura. Elevated δ15N values of G. obscura and similar food source contribution rates between the host and symbiont suggest that ophiuroid feeds on materials filtered by crinoids and have similar diet to the host. Our results provide insights into the symbiotic patterns of crinoids and ophiuroids, while also supplying foundational data on how symbiotic reef species select organic matter utilization strategies to adapt to their environment.

Dogs in Lithuania from the 12th to 18th C AD: Diet and Health According to Stable Isotope, Zooarchaeological, and Historical Data

This article presents the results of research that focused on the nutrition and related health issues of medieval and early modern dogs found in the territory of present-day Lithuania. In this study, we present bone collagen carbon (δ13C) and nitrogen (δ15N) isotope ratios for seventy-five dogs recovered from seven sites which were dated back to the between the 12th and 18th C AD. In addition, by studying the remains of almost 200 dogs, we were able to estimate changes in the sizes and morphotypes of canines across over 600 years. On the basis of stable isotope and historical data, as well as the osteometric analysis, we discuss the dietary patterns of different sizes and types of dogs from the sites related to different social strata and time periods. The results of our study demonstrate that the size, type, diet, and health of canines from different time periods and sociocultural environments varied. Overall, carbon isotopic signals indicate that dogs' diets were based on C3 plant environment foods (cereals and animals), while freshwater fish was more important for some individuals in coastal Klaipėda/Memelburg Castle. The stable isotope analysis supported the historical records, indicating that cereals were highly important in the diet of elite dogs. Meanwhile, urban dogs had a different nutrition. In the Middle Ages, the consumption of plant-based foods was likely higher compared to the early modern period. Our study also revealed that the diets of dogs did not correlate with individual size. Compared to pigs, dogs had a higher intake of animal foods in their diet. In general, the nutrition of the studied canines was similar to that of the rural human population of the same period.