Determinants of heart rate in Svalbard reindeer reveal mechanisms of seasonal energy management

Abstract

Seasonal energetic challenges may constrain an animal's ability to respond to changing individual and environmental conditions. Here, we investigated variation in heart rate, a well-established proxy for metabolic rate, in Svalbard reindeer ( Rangifer tarandus platyrhynchus ), a species with strong seasonal changes in foraging and metabolic activity. In 19 adult females, we recorded heart rate, subcutaneous temperature and activity using biologgers. Mean heart rate more than doubled from winter to summer. Typical drivers of energy expenditure, such as reproduction and activity, explained a relatively limited amount of variation (2–6% in winter and 16–24% in summer) compared to seasonality, which explained 75% of annual variation in heart rate. The relationship between heart rate and subcutaneous temperature depended on individual state via body mass, age and reproductive status, and the results suggested that peripheral heterothermy is an important pathway of energy management in both winter and summer. While the seasonal plasticity in energetics makes Svalbard reindeer well-adapted to their highly seasonal environment, intraseasonal constraints on modulation of their heart rate may limit their ability to respond to severe environmental change. This study emphasizes the importance of encompassing individual state and seasonal context when studying energetics in free-living animals. This article is part of the theme issue ‘Measuring physiology in free-living animals (Part II)’.

Heart rate as a measure of emotional arousal in evolutionary biology

“…For example, when transporting sheep, heart rate revealed differences in the perceived stress depending on the methods of driving and loading sheep [99,100], and cognitively enriched pigs have a lower heart rate during feeding announcement compared to a control group [101]. Recently, heart rate measures have also been implemented in precision livestock farming, defined as the use of advanced technologies for continuous automated real-time animal monitoring to optimize the contribution of each animal [58][59][60]102,103]. In future, heart rate could be used on a large scale to identify early signs of decreased welfare or poor health in groups of farmed animals, pets or critically endangered animals in a conservation context (table 1).…”

“…farm animals, animals in shelters), be linked to outcomes of daily routines or veterinary inspections. Long-term monitoring of heart rate would also allow us to disentangle short-term reactivity to environmental stimuli from long-term activation of the physiological stress response, which is not well understood yet [11,103]. Heart rate recordings could be incorporated in automated health surveillance processes in a wide variety of different settings [114,115].…”

Near-Infrared Spectroscopy as a Tool for Marine Mammal Research and Care

“…Prior to NIRS, electrocardiography (ECG) has been used for decades on various free-ranging species to monitor heart rate ( Butler and Woakes, 1980 ; Thompson and Fedak, 1993 ; Trondrud et al, 2021 ). Similarly, blood oxygen measurements in free-ranging animals such as seals, sea lions and penguins, pioneered by Paul Ponganis and colleagues, have been achieved with great success using intravascular-dwelling Clark-type pO 2 electrodes ( Ponganis et al, 2007 ; Meir et al, 2009 ; McDonald and Ponganis, 2013 ).…”

Stress responses to repeated captures in a wild ungulate

“…There are many research questions of importance for conservation, management, and basic research, that cannot be answered without repeated captures. For example, our own study of the daily energy expenditure in wild Svalbard reindeer, which enhanced our understanding of energy balance during the food-depleted winter in this high-Arctic species experiencing rapid climate change 3,58 . Overall, this capture regime appears to have elicited a sensitized, short-term stress (hours to days) responses but with minor long-term consequences.…”