The Oryx gazella - AKA - The Gemsbok Pictures taken in the Okonjima Private Nature Reserve - Namibia: Photographer: Wayne Hanssen - Oct 2014 The range of gemsbok, Oryx gazella, mostly consists of southern east Africa, though formerly the range included South Africa. Gemsbok are able to increase their body temperature to 45 degrees from 35.7 degrees C in order to delay evaporative cooling. . . . but now there are thoughts on new science. . . see: frantic-naturalist.blogspot/2010/02/cool-headed-oryx-thoughts-on-new.html The Southern Oryx or Gemsbok, the sub-species of Oryx gazella that we find in Southern Africa must have some specific adaptations to arid conditions. Some of the popular ideas about this, however, appear not to be correct in the face of new studies. An animal living in a desert environment has two main problems that feed off each other...dealing with heat and dealing with a lack of moisture. By a long way the best way to deal with heat is through some form of surface cooling through evaporation off the surface of an animal. In mammals...sweating. Works great, but what if you have a very limited water supply...obviously sweating becomes expensive. Adaptations that relate to dealing with this double problem (heat/moisture scarcity) come in two forms, and again it is a little obvious...gain more moisture and loose less moisture. It may be obvious, but it helps to look at it like that. And of course, the implementation is a little more tricky than the concept. A popular idea for many years was that Oryx could do something really amazing...that they could choose to stop sweating and use brain cooling through the carotid rete system. But, one small problem with this popular idea is that it appears not to be true. . . . ?? The idea went something like this - Veins from the nasal cavity cools arterial blood going to the brain in a network of blood vessels called the Corotid Rete. This method of brain cooling occurs in a number of mammals. It was believed that Oryx could simply choose to stop sweating and let their body temperature go, even beyond mammalian norms, and have the brain stay cool enough by using this system. The idea was proposed based on the anatomy of the brain, not because of temperature measurements. That was mainly because you couldnt measure the brain temperature of an animal living outside for a period of time as it went through its normal duel with the environmental conditions. But now it is possible. Small data loggers can be inserted into the brain and give an accurate picture of just how much this cooling actually does. What they are finding is that the cooling effect is minimal, and not enough to allow Oryx to stop sweating. Whats more, the body temperature of the animals are higher at night, rather than in the day time. The Corotid rete does assist in survival in hot, dry places, but most likely, I take it, for periods of high activity, such as running away from a predator. Reference: Note: I didnt intend to write a blog post about this when I was first reading about it, and cant remember all the links I visited. I started out just trying to understand the functioning of the theory as it was, a little better. It soon became apparent that the whole thing was based on a number of assumptions, and so I started trying to dig a little deeper. The carotid rete and artiodactyl success: rsbl.royalsocietypublishing.org/content/4/4/415.full The eland and the oryx revisited: body and brain temperatures of free-living animals: sciencedirect/science/article/pii/S053151310401533X jeb.biologists.org/content/215/22/3917.full
Posted on: Wed, 05 Nov 2014 19:03:32 +0000
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