Physiology: the transfer function between stable isotope analysis & ecology
How does shark physiology affect the biological parameters for interpreting stable isotope data?
The vast majority of captive feeding studies use mammals, birds, or fish because they are easy to keep in captivity. However, shark physiology differs from each of these taxa because they are aquatic ectotherms, have carnivorous diets, retain urea, have cartilaginous skeletons, and use lipids for buoyancy control. These physiological traits impact the metabolic biochemistry and therefore biological parameters of discrimination factors and tissue incorporation rates. Interpretations of ecological patterns and processes requires tissue and taxa specific biological parameters, which may differ with protein quality, growth rate, and allometric scaling. Much of this work is uses specimens from a captive feeding study with leopard sharks at UC Santa Cruz.
What physiological factors affect metabolism and hence, the variation in trophic enrichment factors and incorporation rates?
Most captive experiments have individuals of similar age classes and diet, but there is still variation in the stable isotope data. There are studies comparing juveniles and adults as well as protein quality and quantity, but other factors also influence energy balance and metabolic biochemistry. My first endeavor to characterize one aspect of this variation is in collaboration with Dr. Jessica Santollo related to gonadal hormone status using rats, a well studied model organism.