Thermoregulation and melanistic animals

What I want to highlight today is how environment and temperatures can have an effect on animals coloration. I how talked about how predation can cause a selection pressure on animals, so they respond in developing colors that either warn off predators, or make the prey less visible in their environment. But sometimes there are other things that can create a selection pressure as well. This might include colors that attract a mate, or colors used for thermoregulation. I will dig deeper in to thermoregulation today.

Some animals are what we call ectotherms, they are dependent on the temperature and heat energy around them, to maintain there metabolic rate and for development, growth and movement. These animals need to actively move in to sun to heat up, and to find shade and cooler environments if they get to hot. This is behavioral thermoregulation. In some environments, like high altitude areas, the temperature might not get very high, and the sun might not be up for many hours(for example in the northern hemisphere). This means that animals might have a hard time rising their temperature enough to be active and retain their metabolism, and development and growth will be slow. In these environments the reduced temperature and energy available, might have a bigger impact on selection pressure than mate selection and predation will have, if you compare it to more favorable environments with higher temperatures. This will have an impact on animals coloration, because a small difference in color can make a huge difference in the levels of activity, growth and development, and therefor make an animal more successful. Dark colored animals will obtain more energy from the sun, they heat up faster, and then they have more hours for disposal during a day, and obviously this is an advantage.

Researchers studied a butterfly larva in cold and warm environments, and concluded with some interesting facts(Lindstedt et al. 2009). The larvae they studied showed patterns of orange to deter predators(aposematism- warning colors), and in favorable environments the most successful larvae was the larvae with most conspicuous colors, this because it is easier for predators to see, and more predators avoid them. But in colder environments they found a trade off, because the most successful larvae here, where those with smaller patterns and darker colors. These were more active and developed faster, and showed faster growth. As mentioned in the report:' Benefits of shorter development and growth at faster rates, can be significant, because it decreases the period when a larva is vulnerable to predation and parasitism, and increases the probability of individual surviving until reproductive life stage'.

A researcher from Stellenbosch University in Africa, Susana Clusella-Trullas, studied coloration among lizards in Africa, and published her study in Ecology in August 2009. She found that darker colored lizards in cooler environments where more successful compared to the paler once, because they were able to be longer active during the day. Bellow is a link to an interview with her, where she explains what she found and how she managed to do the research. It is very interesting.

https://www.esa.org/fieldtalk/its-only-skin-deep-melanism-and-thermoregulation-in-lizards/

There is other examples of animals that use color to regulate there temperature as well. There has been research on chameleons(Bennett 2004), where they found that different colors are not just used as camouflage, but also change of color is due to temperatures. When the chameleons are feeling cold and the sun rises in the morning, they will show a dark skin color to heat up faster, and when their favorable temperature is reached, they will change color so they become more pale, and less energy is absorbed. This is a very interesting and fascinating adaption, that truly seems to work well.

I also have some examples from Norway where I live. We have this species of spider in the orb weaver family that is found in coastal habitats as well as high latitudes up in the mountains. It is very common many places in Norway. What is interesting, is how the color changes when you reach higher altitudes. Close to the coast the spider is displaying a white coloration with some black stripes on its legs and some black markings on the abdomen. But up in the mountains, you will find it to be totally black. The temperatures here are much lower compared to the coast, and to survive the spider needs to be able to gain as much energy from the sun and the surroundings as possible. We also have a snake in the wiper family, that normally shows a black zig zag pattern on its back, against a pale background color on the rest of its body. This pattern seems to be less visible on higher altitudes, due to more individuals with darker skin, some are almost entirely black. Zig zag patterns are often believed to act as a warning or to play a part in motion dazzling, but up in high altitudes this becomes less important, and there is a trade of between this pattern that gives decreased predation risk, an being melanistic where the snake can develop and grow faster, and be more active and catch prey easier.

Below is a picture of the snake where the pattern is visible, and the other one is the melanistic type. The species is Vipera berus .

Illustration 1: Normal snake

Illustration 2: Melanistic snake

Below is the spider Larinioides cornutus with different colors.

Illustration 3: Photo: Glenn Halvor Morka

Illustration 3: Photo Jostein Gohliu

References:

Illustration 1: http://no.wikipedia.org/wiki/Hoggorm

Illustration 2: http://no.wikipedia.org/wiki/Hoggorm

Illustration 3: http://www.edderkopper.net/Araneidae.html

Illustration 4: http://www.edderkopper.net/Forum/smf_1-1-11_install/index.php?topic=4308.0

Lindstedt, C, Lindström & L, Mappes, J 2009, 'Thermoregulation Constrains Effective Warning Signal Expression', Evoultion, vol.63, no.2, pp.469-478, viewed 26 April 2014, <http://www.jstor.org.elibrary.jcu.edu.au/ >

Bennett, AF 2004, 'Thermoregulation in African chameleons', International Congress Series, vol.1275, pp.234-241, viewed 26 April 2014, <http://www.sciencedirect.com.elibrary.jcu.edu.au/ >