Keep Cool and Speak Dolphin
The fluctuating, symphonic buzz of locusts, the splashing water of a nearby bathing robin, and the piercing beams of the sunshine remind me it's July again in the Midwest. As a climate-change-induced heatwave rages around the world, humans respond by fleeing indoors, cranking the air conditioning, and taking cold showers. Animals, however, do not have the luxury of AC, except for some domesticated pets. So how does Nature keep at an ideal temperature during the summer heat yet keep warm come January? Thermoregulation, as it's called, has various solutions in Nature so let's explore.
If you live in a coastal town, you may keep cool on the beach from the ocean breeze while observing dolphin fins cresting on the horizon. During a recent snorkel trip in Costa Rica, we watched dolphins swim around and follow alongside our boat. This behavior of dolphins is counter-intuitive to some creatures that instinctively swim away from humans. The dolphin intelligence and empathetic communication methods parallel humans closely. Another similarity between dolphins is maintaining their core temperature close to that of a human's core temperature. To do so, the Bottlenose Dolphin (Tursiops truncatus) utilizes three strategies for thermal regulation; a heat sink, countercurrent convection, and conduction.
Its fat, also called blubber, acts as an insulator at cold water temperatures and a heat sink at warm water temperatures. It consists of different fat molecule types that change from solid to liquid at different temperatures1. When solid converts to a liquid, heat is absorbed during the process and vice-versa when converting from liquid to solid. These solid-liquid-solid phase changes create a unique method of thermoregulation. A second thermoregulation strategy of the Bottlenose Dolphin involves thermal windows in its dorsal fin, ventral fin, and flukes where blood flows in the opposite direction of the dolphin's direction of travel(2). This countercurrent flow control provides an efficient method of liquid-to-liquid heat transfer. The thermal window resembles a car's radiator by actively pumping the heated engine coolant into the cooling airflow in the front of the vehicle (water-flow in the dolphin case). Finally, the dolphin's conductive and flexible skin aids in the transfer of heat from inside its body to the outside environment where the cooling seawater comes into contact with its skin(3). Interestingly, this heated layer of water on the outside of its skin improves its hydrodynamic performance, thus providing more efficient swimming.
Bottlenose dolphin thermoregulation diagram by Nature Comes Standard LLC
So what can humans sustainably learn and create from the three-tiered thermal regulation system of the bottlenose dolphin? Perhaps new activewear? An improved laptop processor heatsink? An innovative cooling system for a public transportation power generation? The biomimetic applications are endless. What would you design?
References:
Barbieri, M.M., McLellan, W.A., Wells, R.S., Blum, J.E., Hofmann, S., Gannon, J., Pabst , D.A. (2010) “Using infrared thermography to assess seasonal trends in dorsal fin surface temperatures of free‐swimming bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida” Marine Mammal Science. Vol 26, Issue 1
Hoover, A.P., Griffith, B.E., Miller, L.A., (2017) “Quantifying performance in the medusan mechanospace with an actively swimming three-dimensional jellyfish model” Journal of Fluid Mechanics. Vol: 813: 1112-1155
Tian, Limei, Jin, E, Mei, Haoran, Ke, Qingpeng, Li, Ziyuan, Kui, Hailin (2017) "Bio-inspired Graphene-enhanced Thermally Conductive Elastic Silicone Rubber as Drag Reduction Material” Journal of Bionic Engineering 14:130–140
