Heat transfer control by cold-blooded organisms

Since centuries, people living in areas with cold winters have been trying to economize the energy required to keep their homes warm. Traditional alpine houses were constructed in a way that the living area was above the barn where animals produced enough heat to warm up the ceiling for several degrees. This required much less additional heating in the first floor as if the house was set on cold soil.

Afterwards, the development enabled efficient wall insulation, central heating system, floor heating, good isolating windows, etc…..Energy loss has therefore been sufficiently reduced and today people can confortably inhabit places with extreme conditions.

Animals and plants do not have such technological advantages. In the course of evolution they had to develop different strategies to survive in ice cold temperatures, meters of snow and harsh winds. In this article I will focus on a reptile which lives in Alps and whose complex morphological and behavioural adaptations are its key for success.

This animal is the Common European adder (Vipera berus), a worldwide venomous species with the largest geographical distribution among all snakes. It can be found from the United Kingdom to the Pacific coast of Asia. They are found as far north as the Arctic Circle and as far south as the Mediterranean Sea [1]. Even though they are ectotherms (cold-blooded = their body temperature depends on the temperature of the surroundings) they inhabit high altitudes up to 2600 m [1]. In the wild they can live 10-15 years. In general, a female gives birth to 12 neonates which need 3 to 4 years to grow up. At adult age they can grow as long as 80 cm. The mass of male adders generally ranges between 50 to 70 grams, while the mass of females ranges from 80 to 100 grams [2].

 

Morphological adaptations:

The temperature regulation of snakes is managed through two different morphological adaptations. The first one is “coloration or melanism”. Individuals at higher altitudes are mostly darker than other adders of the same species living lower. The melanistic adder is completely black while his relative has a typical dark zig-zag pattern on a brighter basis. Black colour absorbs more visible and infrared light which results in faster heating and therefore lower predation costs and faster growth. The second adaptation are keeled scales. Keeled dorsal scales have mid-centered ridges and thus reduce shininess (lower reflectance). They contribute to structural strength and the animal’s overall camouflage. On the contrary, ventral scales are very wide and smooth and serve for locomotor performance (Figure 1).

Screenshot 2016-01-12 15.31.24

Figure 1: Keeled dorsal scales and smooth ventral scales. The first ones have a significant effect on heat transfer.

 

Behavioral adaptations:

In order to survive, adders have developed a temperature-regulative behaviour through

  • hibernation: Only adders at higher altitudes hibernate during winter. Up to 100 snakes can be found in thermally buffered hibernacula where they spend 5-7 months. Males come out 3 weeks before females and perform active spermogenesis [3].
  • viviparity (is development of the embryo inside the body of the mother, eventually leading to live birth, as opposed to laying eggs): Females can buffer the ambient thermal variations in their uterus. Higher temperature is directly related to the number of ventral scales defining the fitness of an individual [4].
  • basking: Snakes have to expose to the sun in order to warm up. They gain heat by radiation, conduction and convection. Their goal is to reach a preferable temperature for digestion and locomotion. Their metabolism increases exponentially with ambient temperature. Their heat exchange is controlled by the time spent in the sun, reflectance and surface are. To maximize heat absorption, they use the “surface to weight ratio” principle – they flatten their body and stretch out to collect as much warmth as possible while in cooler weather they coil into a close spiral to reduce heat transfer (see Figure 2).
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Figure 2: Temperature-regulative behaviour for heat transfer control and relation between external and snake’s body temperature

Techinical implemenation:

It is worth to take a look at energy systems of living organisms from extreme environments because they have optimized adaptations for heat transfer. Adders offer much but honestly, behavioural adaptations are way too complicated to be transferred in our technology. Morphological solutions are much more useful because they are based on physical laws and keeled scales might be possble to be applied in technology.

The first generation of solar collectors is still widely used but their efficiency is low due to great thermal losses through the glass and backside insulation. Their thermal response is relatively slow and they perform even worse in cold period. At intermitted sunlight they are not able to heat up sufficiently. To reduce the losses, a glass surface could be keeled (inspired by the Common European adder) in order to reduce reflectance and therefore collect more light. To improve thermal response, pipes could flatten at lower temperature and contract with increasing temperature.

kolektor

Fig. 3: Possible influence on heat transfer via reduced reflectance of glass

It may look like that such applications could improve the efficiency of current technology for some percents (or not even) due to reduced reflectance. But the question always arises in relation to production costs. Customizing the surface of the glass used for solar panels would increase the costs and the outcome might not be as cost-efficient as desired. Definitely, an expert’s opinion or a real experiment would tell much more. If not for us, it works very good for the adder!

 

 

References:

  • [1] Wirth M., Common Vipers of the Northern Black Forest, Reptilia, 24-29
  • [2] Vipera berus, 12.1.2015
  • [3] Herczeg G. et al. 2007, Suboptimal thermoregulation in male adders (Vipera berus) after hibernation imposed by spermiogenesis , Biol. Jour. of the Linnean Society, 92, 19-27
  • [4]  Lindell L.E. et al. 1993, Variation in number of ventral scales in snakes: effects on body size, growth rate and survival in the adder, Vipera berus, J.Zool. 230, 101-115
  • Fig. 1: Vipera berus, Adder, 12.1.2015
  • Fig. 2: Smith T.M., Smith R.L. 1955, Elements of Ecology, 7th Edition, Pearson Education

 

Anja Soklič

My name is Anja and I come from one of the most beautiful places on the world – Bled, a small town in a very small country called Slovenia but very beautiful! Imagine that in two hours you can traverse this country, passing high mountains, numerous rivers and lakes, valleys, vineyard hills, and finish on the coast. No wonder why I decided to start my studies in relation to nature.

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