Animals Adaptions To Extreme Environments
Introduction
High altitude is defined as being over 2500m (Bigham, 2016). Organism that live at high altitude can be aerial, aquatic, terrestrial and soil-borne. Adaptions to high altitude can either be a short-term response to acclimatise or an evolved, long-term irreversible adaption. Long-term adaptions are held within the genome of high altitude species. The main issues that impact organisms at high altitude are low pressure, low oxygen and low temperature, the organisms must adapt accordingly (Storz et al, 2010). Mammals. There are over 140 Million people living in high altitude regions, these include Tibetan, Ethiopian and Andean populations (Moore, 2017). Acute mountain sickness (AMS) occurs in non-adapted individuals.
This can lead to vomiting, headaches, fatigue, nausea, palpitations, pins and needles, nose bleeds and shortness of breath. Illness’ such as high altitude cerebral edema and high altitude pulmonary edema are more serious and can lead to coma and death. Prescription treatments such as Tadalafil and Salmeterol (Subhojit et al, 2018). The residence of these high altitude regions have an increase in red blood cell mass due to there being reduced oxygen (hypoxia) in these areas. These populations are somewhat resistant to AMS. This seems to be due to natural selection in these regions being related to the hypoxia-response pathway (Crawford et al, 2017). Populations of the Tibetan plateau have adapted to having darker skin tones due to higher UV radiation at the increased altitude, they have also adapted to having a higher birth rate so that they can survive in their environment (Zhang et al, 2012). The yak (Bos grunniens) is heavily adapted long-haired bovid. They are primarily found in the Tibetan highlands between 4000-5000m in alpine steppes, desert steppe grasslands and alpine meadows. It is estimated to be 22’000 yak in china which is 90% of the population. Bos grunniens is designed to be compact to preserve body temperature.
They have short legs and long hair as other adaptions to preserve heat. As for hypoxia adaptation they have more haemoglobin, more red blood cells, a stronger heart, higher stroke level and faster circulation. Bos grunniens have a larger chest cavity and a shorter but wider trachea compared to other Bovidae species in order to enhance respiratory rate. They have serrated creases and wrapped shells on their hard circular hooves to navigate their habitat (Shi et al, 2016). The Snow leopard (Uncia uncia) is a predator that lives in high altitude regions. It shows many adaptations to its environment. Uncia uncia has grey-white fur with patterned grey spots, this allows it to blend in with the snowy and mountainous environment in which it exists. It has long hair with a more woolly type of fur on its underside to keep warm in the cold weather. Uncia uncia have well developed chest muscles for climbing the mountainous terrain and a larger nasal cavity to take in more oxygen. A lot like other species discussed they have short stocky limbs to maintain their body temperature. The tail of Uncia uncia can be up to 1 metre long and is used to balance when traversing their habitat as well as to keep them warm. They wrap their tail around themselves for warmth (McCarthy et al, 2003). Birds. The bar-headed goose (Anser indicus) travels over the Himalayas twice per year while migrating between the south of Asia and central Asia.
The oxygen at this altitude can be up to five times less than sea level. Anser indicus has adapted to physiologically control their breathing and metabolism. They breath more and with a more effective breathing patterns than low-land birds. This allows more oxygen to get into the blood stream. Anser indicus can lessen the impacts of high altitude on their body temperature and metabolism ( Milsom & Scott, 2008). They have a larger heart to pump blood around and larger lungs to take in more oxygen. It has been shown that in general aviary lungs have a greater gas exchange capacity than mammalian lungs. Birds also have a different pulmonary vessel physiology that may contribute to resistance to the acute mountain sickness that occurs in other animals. The heart and brain composition are also adapted to resistance to hypoxia (Scott et al, 2015).
Fish & Reptilians
As altitude increases absorbable oxygen for fish decreases in lakes and streams. This causes a decrease in the diversity of fish species in these environments. The water is in fact more oxygenated as oxygen can dissolve better at higher altitudes (Jacobsen, 2008). High altitude frogs such as the Andean water frog (Telmatobius culeus) live in aquatic environments. These anurans can be over 50cm in length and 1kg in weight. They have the highest amount of red blood cells and lowest metabolism of all anurans which is an adaption to their environment, something we have seen as an adaptation of all high altitude animals. Telmatobius culeus has oversized skin that has a lot of capillaries that allows the frog to respire in the cold water it lives in. It stays at the bottom of the water and bobs up and down to let the high oxygenated water to pass over its skin so it can absorb the oxygen. This can only happen due to the frogs adaptations and the altitude it lives in. If one of these frogs were moved to a lower altitude it would have to surface to get oxygen (Navas & Chaui-Berlinck, 2007). It has been shown for none aquatic reptiles that the high altitude species spend a longer amount of time basking to thermoregulate body temperature (Caldwell et al, 2017). The trend of having a lower metabolic rate is shared by non aquatic reptiles, this can be seen in the Toad-Headed (Phrynocephalus vlangalii) (Liang et al, 2017).
Due to the lower metabolism these reptiles have a lower locomotion rate and sprint speed than their lower altitude counterparts. Less predation pressure and less need to hunt could also be attributing to locomotion and sprint speed (Wu et al, 2018).
Invertebrates
Free-flying insects typically do not ascend higher than 5000m. They get this high by riding air currents when migrating. Some species and butterflies have been found closer to 6000m. Alpine bumble-bees ( genus Bombus) are different, they forage and nest around 4000m and have been found in access of 9000m. Adaptions that alpine bumble-bees have made are that they change their wingbeat frequency and they increased their stroke amplitude by 20°. These adaptions offset the effects of high altitude and reduced atmospheric pressure (Dillon & Dudley, 2014).
The Himalayan jumping spider (Euophrys omnisuperstes) has been found as high as 6750m (Brandenburg et al, 2017). This spider is a dark brown to black colour with a metallic head. It has pale brown to white hairs. Spiders at this altitude unlike other organisms don’t appear to have many adaptions to their environment, they are much the same as species of spider who live at lower altitudes (Wanless, 1975). Euophrys omnisuperstes feed upon spring-tails that have been carried up by air currents (Swan, 1961). These spring-tails (Hypogastrura harveyi) have a unique adaptation in which they create an anti-freeze protein to deal with low temperatures (Lin et al, 2007).
Conclusion
It can be seen that adaptions to high altitude are split between vertebrates and invertebrates. Most vertebrates that have genetically evolved to live at high altitudes have thick fur, long hair as well as respiratory and circulatory adaptions (Weber, 2007)(Navas & Chaui-Berlinck, 2007)(McCarthy et al, 2003). Less is known about invertebrates but they seem to short-term acclimatisations and a wider variance of long-term adaption. This can be seen by Euophrys omnisuperstes having long hair adaptions and Hypogastrura harveyi with their anti-freeze proteins (Wanless, 1975)(Lin et al, 2007).
