An Integrative Approach to Evaluating Metabolic indicators in Maned Wolves (Chrysocyon brachyurus)

Abstract

Integrated datasets of physiology and behavior are critical to determining the impact of environmental threats on animal health. Continued advancements in biologging technology aid this effort; however, additional techniques, such as endocrinology, can help contextualize findings. Maned wolves (Chrysocyon brachyurus) experience broad-scale landscape alteration, presenting a need for reliable indices of metabolic health. I tested a protocol for long-term monitoring of metabolic health in free-ranging wildlife by integrating biologging and analysis of hair triiodothyronine (T3), a form of thyroid hormone, using captive maned wolves as a model. Hair samples were collected approximately every three months for just over one year from maned wolves (n=8) implanted with Reveal LINQ™ (Medtronic Inc., Minneapolis, MN) biologgers at the Smithsonian National Zoo and Conservation Biology Institute in Front Royal, Virginia, USA. Daily average heart rate (HR) and heart rate variability (HRV), and daily total activity were calculated from raw biologger data. T3 was measured in guard hair via a T3 enzyme-linked immunosorbent assay (Arbor Assays, MI), which passed analytical validations for maned wolf hair extract. To evaluate the feasibility of integrating these measures, I tested the impact of various determinants of metabolism (e.g. season, ambient temperature, activity, food intake, and body weight) on HR, HRV, and hair T3. I detected seasonal patterns in all metabolic indicators. Notably, HR increased and HRV decreased in winter, indicating increased activation of the sympathetic nervous system, and by inference, increased metabolic activity. Variation in HR and HRV was primarily explained by ambient temperature. Contrary to predictions, hair T3 was greatest in summer and lowest in winter and was positively impacted by ambient temperature. This may indicate that increased metabolic activity in winter was triggered by types of stressors that are not reflected in circulating thyroid hormone concentrations. Alternatively, apparent hormone concentrations in hair may reflect different time periods than expected or may not reflect plasma concentrations consistently. Ultimately, I demonstrate the feasibility of combining biologging metrics with analysis of T3 in hair, but also highlight the need for further investigation of hair T3 as a potential proxy of plasma T3, and of T3, in turn, as an indicator of energetic state. Because hormones are incorporated into hair as it grows, may be a particularly valuable sample type for retrospective analysis of animals’ physiological state over time. Thus, this integrated assessment of biologging parameters and endocrinology shows promise for application in situ, in combination with other ecological assessments, as the field aims to understand how free-ranging maned wolves’ meet the energetic demands of altered landscapes.