The Effects of Stress on Animals

It's ironic that I'm about to talk to you about the effects of stress on animals because I currently look like this:

On a more serious note.. stress can be a very important measure of animal welfare. Stress can potentially show that there is a problem with the animal's welfare, particularly in captive environments. For example in a zoo with a monorail going over an enclosure, if an animal becomes stressed every time the monorail goes over it can indicate that the monorail is having a significant detrimental effect on their welfare.Stress is an important process as it allows the body to adapt to change. The stress response is triggered by a threat such as a decrease in temperature. This causes the hypothalamus in the brain to release corticotropin-releasing hormone (CRF) which travels to the anterior pituitary. CRF controls the release of adrenocorticotropic hormone which stimulates the adrenal cortex to secrete cortisol.

Cortisol is responsible for the body's response to stress. The cells which are not needed for what we call the "fight or flight" response are stimulated by cortisol so that they decrease their use of blood glucose and start using fats and proteins for energy instead. Processes such as immune system reactions are also turned off as they are not needed to cope with the stress. Metabolic rate is therefore increased and life-sustaining processes have more energy. Cortisol is a type of Corticosteroid which are used in stressful circumstances. Corticosteroids stimulate glucose production from fat (as mentioned above), break down the tissue protein, increase the sensitivity of the blood vessels to adrenaline (to allow fight or flight), increase the rate of urine formation, make muscles function for longer, affect brain excitability, increase gastric acid and pepsin secretion, act as an anti-inflammatory and suppress the immune system (as mentioned above). Once the stress response has served its purpose cortisol effects the cells of the brain which causes a decrease in the release of CRF in a negative feedback loop.

The effect of stress on the body has three different stages depending on the length of time the stress is present. The first stage is called the Alarm Stage. This is when the body first reacts to the stress and it's response is in a state of alarm. At this point adrenaline is produced so that the fight or flight response can be used. There is also some activation of the HPA axis, producing cortisol. If the stressor persists then the body begins to adapt to the change and this is called the Adaptation Stage. However, if the stressor persists for too long then the body enters the Exhaustion Stage and it's resources become depleted. This can cause long term damage to the individual with effects such as ulcers, depression, diabetes or cardiovascular problems and it must therefore be avoided at all costs.

The physiological processes which occur when an organism is stressed allow us to measure welfare effectively by taking measurements of cortisol or other corticosteroids. This allows for improvements to be made to a captive animals environment using enrichment. It can also be combined with behavioural welfare assessments to get a better result.

Glowing Mushrooms and Fireflies

I've been neglecting you dear Zoology blog. I am very sorry and I am going to try and post on here at least once a week to keep on top of my extra reading. This evening I would like to talk to you about a very interesting subject I had a lecture on this week, bioluminescence. Many of us will have seen examples of bioluminescence (without knowing the fancy word for it) in fireflies and some people may also have seen glow worms. The majority of bioluminescence however is found in the oceans.

animals.nationalgeographic.com

As you would expect, it is very hard to see when you live in a deep sea habitat. The photo above is a Anglerfish which lives in very deep regions of the ocean and looks very much like a scary alien from a sci-fi movie! As you can see, the Anglerfish has a lure which has a light on the end. If you have ever seen Finding Nemo you will know that it uses this lure to attract smaller fish for it to eat. Dragonfish have a similar lure which goes underneath them rather than over their mouth. Dragonfish also have a light next to their eye which is a wavelength that only they can see. This is a pretty nifty way of being able to see both predators and prey without them seeing you.

tech.ca.msn.com

Bioluminescence is also helpful for marine organisms avoiding predators. The Hawaiian Bobtail Squid uses a bacterium (Vibrio fischeri) to create light which it reflects from its body in the same direction as the moonlight and therefore obscures its silhouette in the water and makes it difficult for predators to see them. The image above is the deep sea octopus (Stauroteuthis syrtensis) which is one of the very few bioluminescent octopuses. Strangely, it is the suckers on this octopus which light up and the function of this is not yet known but could be to either attract prey or for communication. The bioluminescence shown in ocean species is generally either blue or green as these are the colours that travel the furthest. In terrestrial organisms the colours can vary greatly.

animals.nationalgeographic.com

As I mentioned earlier, fireflies are a well known example of bioluminescence and are one of the few terrestrial examples. Since fireflies are usually seen as little glowing dots I thought I would give you a close up picture of one. Different species of firefly use different colours of light depending on the time of day they use their light and the ability of that particular species to see different colours. Many species emit red light but we only see yellow or green light due to our eyes. These organisms use their light to attract mates so they can reproduce, which is very different from the marine organisms we have already talked about.

Wikipedia

Finally I would like to talk to you about bioluminescent mushrooms. That's right, glowing mushrooms. The picture above shows a tropical fungus which is often found on decaying matter such as wood or leaves. When conditions, such as temperature and water content of the soil are right, these fungi glow. At night insects are attracted to the fungi and carry away spores which are then dropped somewhere nearby. This allows maximum growth of the spores due to the good conditions.

Bioluminescence is a very interesting subject that is still being researched. It is unknown why many organisms spend so much energy on producing light and studies are currently going on to help us discover more about this fascinating subject. The animals I have mentioned about are only a few of the many examples of this phenomenon and many are still being discovered.

References:

•  Deheyn, D.D., Latz, M.I., 2007, Bioluminescence characteristics of a tropical terrestrial fungus (Basidiomycetes), Luminescence, Voll 22, pp 462-467
• Dehingia, N., Baruah, D., Siam, C., Gohain Barua, A., Baruah, G.D., 2010, Purkinje effect and bioluminescence of fireflies, Current Science, Vol 99 (10), pp 1425-1429
• Johnsen, S., Balser, E.J., Widder, E.A., 1998, Light emitting suckers in an octopus, Nature, Vol 398, p113
• Nyholm, S.V., McFall-Ngai, M.J., 2004, The winnowing: establishing the squid-vibrio symbosis, Nature, Vol 2, pp 632-643

How Do Springbok Keep Cool?

www.ultimate-africa.com

Springbok (Antidorcas marsupialus) live in South Africa which, obviously, can get very hot during the day. Many animals that live in Africa tend to try and stay in the shade during the day to keep cool but there are also those that store heat in their body during the day and then let their body temperature decrease rapidly during the night so that the next day they can do the same again. This technique is called adaptive heterothermy and has been seen in often in captive animals. Fuller et al (2005) carried out a study to see whether this technique was also found in wild animals and decided to investigate a free ranging herd of Springbok.

For this study some very impressive technology was used to save time and also to make the results more accurate. Small data recorders where implanted inside each animal and these measured the body temperature of the animals every 30 minutes for a year. If this technology had not been used then the Springbok would have had to have been captured every 30 minutes, every day for a year. Not only would this be very time consuming, it would also affect the results of the study because the animals would likely be stressed about being caught all the time. While the animals were doing their own thing for a year, the team measured the temperature of the air, the wind speed and the humidity so that at the end of the year the body temperature could be compared with the weather.

If the Springbok used the technique described above then the body temperature would be expected to change often with very wide swings. They actually found that the opposite happened. No matter what the weather was like, the body temperature of the animals hardly changed. This technique is called homeothermy and it was a very surprising find. Even stressful events like giving birth did not affect the body temperature a great amount.

This study highlighted a very important point to consider when carrying out experiments on body temperature. When animals are roaming free in their natural environment they often use behavioural mechanisms to change body temperature instead of using physiological mechanisms such as adaptive heterothermy. Behavioural mechanisms like this include huddling together when it is cold or finding a shady area when it is too warm. Fuller and team made a mistake in this study because they did not watch the behaviour of the animals, they only took physiological measurements. Hopefully further studies will be carried out that will learn from this mistake!

References

Fuller, A., Kamerman, P. R., Maloney, S. K., Matthee, A., Mitchell, G. and Mitchell, D. (2005). A year in the thermal life of a free-ranging herd of springbok Antidorcas marsupialis. J. Exp. Biol. 208, 2855-2864.