Effects of Dietary N and Lichen on Body Protein Conservation in Reproducing Rangifer

University Of Alaska Fairbanks Campus, Fairbanks AK

Investigators

Abstract

0136210 Barboza Caribou and reindeer (Rangifer tarandus) are the only ungulates to have successfully colonized both arctic and boreal ecosystems in a circumpolar distribution. These large animals are central to the cultural identity and sustenance of many indigenous peoples throughout the north. Across arctic and sub-arctic landscapes, terrestrial lichens comprise a large proportion of the plant biomass. These assemblages of fungi, algae and cyanobacteria not only contribute to hydrology, nutrient cycling and atmospheric exchanges in the ecosystem, but are also consumed by caribou and reindeer. Pollutants deposited on lichens are dispersed via Rangifer into predators and humans and into soil and water systems along their migration routes. Lichens support many Rangifer herds in the depth of winter and in early spring before the majority of vascular plants resume growth. Consequently, the distribution and abundance of lichens are related to population dynamics and movements of Rangifer. Although lichens contain several potentially toxic compounds, Rangifer and its gastrointestinal microbes can adjust to utilizing the unusual structural carbohydrates in this forage. Exclusive consumption of lichen by captive reindeer, however, can result in mass loss and the net loss of nitrogen (N). Low concentrations of N in lichens may prevent animals from attaining a positive N balance especially at low food intakes. Inadequate dietary N compromises the maintenance of maternal tissues and limits the production of new tissues for fetal growth in pregnancy and milk for calves in spring. We propose a model of changes in body protein for northern deer to relate energy and N balance to dietary supplies. The model predicts changes in the concentration and isotopic enrichment of the catabolite urea in relation to tissue proteins and their products (creatinine, hydroxy proline, methyl histidine). The proposed research will define mechanisms for conserving body N in Rangifer during pregnancy, and quantify a predictive model of body protein loss. Two PhD students will participate in the project. We propose two experiments with repeated measures of captive reindeer fed formulated diets or lichens. The first experiment will determine the dynamics of N through gestation; we will combine measures of food intake and excretion to assess N balance using tracer techniques and isotopic enrichments, with a validation of these methods in non- reproductive animals during spring. The second experiment will focus on the digestive and metabolic responses to lichens; we will determine intake, digestion, digesta flow and absorption, and recycling of waste N. Indirect measures of body composition will be used throughout to determine changes in body protein and fat in relation to diet and season. Describing the interrelationships between lichen ranges and Rangifer populations requires long-term monitoring and management because lichens grow so slowly, but accumulate biomass over many years. This project will provide new data on metabolic responses of Rangifer to the nutritional constraints of northern ecosystems and a tool for understanding the importance of lichens to Rangifer populations. These data will provide a basis for assessing the contribution of migrating herds to N and mineral cycling in tundra systems. Such an increased understanding of herbivore dynamics in the arctic also will have direct implications to other arctic ruminants (i.e. moose and muskoxen) with similar adaptive physiological mechanisms for protein and energy conservation.