How Activity Levels Affect Body Temperature in Captive Dolphins

Jenn Hoskins
22nd June, 2024

How Activity Levels Affect Body Temperature in Captive Dolphins

Risso's Dolphin (Grampus griseus)

Photo adapted from: Charlotte Kirchner / CC BY (Source)

Key Findings

  • The study was conducted on a captive Risso’s dolphin in Japan to understand how activity levels affect internal temperature
  • The dolphin's muscle-blubber interface temperature (Tmbi) increased during periods of higher activity, indicating that muscle metabolism generates heat
  • During rest periods, Tmbi decreased, showing reliance on blubber's insulation to maintain thermal balance
Marine mammals have evolved various strategies to minimize heat loss in their aquatic environments, one of which is the use of blubber. Blubber, a specialized layer of fat, serves as an effective insulator due to its low thermal conductivity. This characteristic creates a significant thermal gradient between the warmer body core and the cooler body surface, effectively reducing heat transfer to the surrounding water. A recent study conducted by researchers at The University of Tokyo[1] sought to deepen our understanding of these thermoregulatory mechanisms by investigating the temperature at the muscle–blubber interface (Tmbi) and its relationship with activity levels in cetaceans. The study focused on measuring Tmbi and activity levels in a captive Risso’s dolphin (Grampus griseus) using an implantable biologging device. This approach allowed the researchers to gather continuous data on the dolphin's internal temperature and activity in a naturalistic setting, providing new insights into how muscle metabolism and physical activity influence thermoregulation. Previous research has shown that blubber's thermal properties vary significantly across different life stages and nutritional statuses in cetaceans. For instance, in Atlantic bottlenose dolphins, blubber from fetuses and emaciated animals exhibited lower thermal insulation compared to sub-adults and pregnant females[2]. These variations highlight the importance of both blubber quantity and quality in maintaining thermal balance. Additionally, the type of lipids stored in blubber can affect its insulative properties. A study comparing pygmy sperm whales and short-finned pilot whales found that blubber with wax esters had lower thermal conductivity than blubber with typical mammalian triacylglycerols, suggesting that lipid composition plays a crucial role in heat retention[3]. Building on these findings, the new study from The University of Tokyo aimed to explore how activity-induced heat production from increased muscle metabolism affects Tmbi in cetaceans. The researchers hypothesized that higher activity levels would lead to increased muscle metabolism, thereby raising Tmbi and enhancing thermoregulation. The study employed an implantable biologging device to measure Tmbi and activity levels in a captive Risso’s dolphin over an extended period. This device provided real-time data on the dolphin's internal temperature and physical activity, allowing the researchers to analyze the relationship between these two variables. The results revealed that Tmbi fluctuated in response to changes in activity levels. During periods of increased activity, the dolphin's Tmbi rose, indicating that muscle metabolism contributed to heat production. Conversely, during rest periods, Tmbi decreased, suggesting that the dolphin's body relied more on the insulative properties of blubber to maintain thermal balance. These findings support the hypothesis that activity-induced heat production plays a significant role in cetacean thermoregulation. The study also found that the temperature gradient within the blubber was essential for minimizing heat loss. By maintaining a higher Tmbi, the dolphin could reduce the conductive heat transfer from its body core to the cooler surface, thereby conserving energy. This mechanism is particularly important for cetaceans, which inhabit cold water environments where heat loss can be substantial. In summary, the research conducted by The University of Tokyo provides valuable insights into the thermoregulatory mechanisms of cetaceans. By demonstrating the relationship between activity levels and Tmbi, the study highlights the importance of muscle metabolism in maintaining thermal balance. These findings build on previous research that has explored the thermal properties of blubber and its role in heat retention[2][3], offering a more comprehensive understanding of how cetaceans adapt to their aquatic environments.

BiochemAnimal ScienceMarine Biology

References

Main Study

1) The variability of muscle–blubber interface temperature with activity level in a captive Risso’s dolphin (Grampus griseus)

Published 21st June, 2024

https://doi.org/10.1186/s40317-024-00375-0

Related Studies

2) The ontogenetic changes in the thermal properties of blubber from Atlantic bottlenose dolphin Tursiops truncatus.

Journal: The Journal of experimental biology, Issue: Vol 208, Issue Pt 8, Apr 2005

3) Lipid class and depth-specific thermal properties in the blubber of the short-finned pilot whale and the pygmy sperm whale.

https://doi.org/10.1242/jeb.071530


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