Tracing Energy Flow Within and Among Organisms
I use bulk tissue and compound-specific stable isotope analyses to study ecophysiology, namely the transfer/remobilization of nutrients during fasting or reproduction in free-ranging marine and terrestrial organisms (Lübcker et al. 2020a, b).
In less than two decades, stable isotope analysis has become a ubiquitous tool to trace ecological processes, yet ecophysiologists have not fully realized the power of this method.
We know that the isotope values of animals are often influenced by more than just ingested resources and that physiological processes associated with key biochemical pathways imprint on the isotopic composition of tissues (Lübcker et al. 2020a, b, 2021). Furthermore, failure to consider physiology may lead to erroneous ecological inferences about energy transfer among organisms that is often used to study species interactions and food web structure (Lübcker et al. 2016, 2017).
I am developing a novel amino acid isotope approach to trace nitrogen balance in response to reproduction and nutrient allocation in birds, reptiles, sea turtles, seals, and baleen whales (Busquets Vass et al. in prep; Lübcker et al. in prep). For example, I am pioneering a technique using carbon and nitrogen isotope values of amino acids in pectoral muscle of females and yolk of their eggs to quantify the reliance on income versus capital breeding at the compound level in a guild of migratory geese that breed in the Arctic in collaboration with Dr. Keith Hobson (Western University, Ontario). Arctic ecosystems are rapidly changing and are ideal locations to study the adaptive mechanisms used by animals in response to shifts in biotic (resource availability/phenology) and abiotic (temperature) conditions.
A new tool for identifying nitrogen balance of free-ranging mammals
It is notoriously difficult to monitor the nutritional status of free-ranging animals over time, particularly those living in the oceans. Whiskers and naturally shed tissues, such as hair or feathers, can be sampled using minimally invasive approaches and are increasingly used for stable isotope-based dietary studies.
Between November and February each year, southern elephant seals (SES) haul out ashore to undergo a ‘catastrophic’ molt. Because the shed hair is potentially synthesized while these animals are fasting, it is possible that the stable isotope values measured in the hair do not provide an accurate reflection of the isotope values of their prey. We found that both the bulk tissue and amino acid δ15N values values of hair, epidermis, and whiskers of SES are adversely influenced by the physiological changes associated with fasting. This was similarly observed in the portion of their whiskers synthesized while on land (Lübcker et al. 2020). See link for more information.
Moreover, fasting also resulted in a large increase in δ15N values for most glucogenic amino acids and a simultaneous depletion of alanine. This finding enabled us to accurately predict (74%) the nutritional status of these animals (fasting versus foraging). While this study adavnces the use of amino acid stable isotopes to observed physiological procesess, it is also evident that physiological factors have an important influence on tissue δ15N values. Not taking this into account can lead to erroneous bulk tissue or amino acid isotope-based reconstructions of foraging habits.