The Importance of Microbes to Animals from Eating to Evolution
Microbes are any living organism that throughout its lifespan is too small to be seen with our naked eye. Most microbes are single-cell organisms. Microbes are the oldest form of life on earth – dating back over 3.5 million years ago when the Earth was still covered with boiling oceans. While microbes are typically thought of as bacteria, microbes can include protists, fungi and microscopic animals. Without microbes, animals could not eat, breathe, or possibly even have evolved at all. Without animals, well, they would probably be just fine. Microbes are important to animals in numerous ways, from eating to evolution.
Most commonly microbes are known for their role in the eating and gastrointestinal process. The mouth or oral cavity of animals has a plethora of bacteria in the saliva to help break down food while ingesting and/or chewing. Microbes in the gastrointestinal (GI) tract assist in the digestion of food. Substantial research has been conducted on the role of bacteria and other microbes in dogs and cats. (Kil and Swanson, 2011; Suchodolski, 2011). Additionally they help protect the animal from infection in the GI tract. They also help the animal synthesize essential nutrients so they can be provided in a usable form to the animal. Specifically for animal nutrition, the decomposition of complex carbohydrates is essential for nutrition. This decomposition of complex carbohydrates and plant structural polysaccharides (e.g. cellulose) is accomplished almost solely by microbes. (Leschine, 2016).
In some animals the dependency on microbes has evolved into symbiotic relationships. The squid-vibrio symbiosis is one example. (McFall-Ngai, 2014). In surgeonfish microorganisms residing in their long GI tract breakdown food by fermentation which is the anaerobic breakdown of the organic compounds. Because guinea pigs are coprophagous (eat their own feces) allowing them to recover essential nutrients and digestive microbes, guinea pigs have a symbiotic relationship with Metabacterium polyspora which allows the life cycle of the Metabacterium to continue in the host or in new hosts. Gorillas also have a type of symbiotic relationship with bacteria that aid in fermentation in the digestive tract. Symbiotic relationships between microbes and their hosts allow the animals to maximize the nutritional benefit from the foods they consume. (Cornell, 2016).
In addition to digestion, microbes may play a critical role in communication between animals. For example, it has been reported that microbes may actually speed-up or boost neurotransmitter signals by causing an increased production in the proteins used to make synapses. Other examples of communication via microbe have been discovered. A specific microbe found in desert locusts aid in induction of crowding behavior of the locusts. (Pennisi, 2015). Researchers also discovered that bacteria living in hyenas' scent glands may produce varying odors so that hyenas can tell their kin from non-relatives. (Dance, 2016). Cockroaches have a similar communication method. The bacteria in cockroach feces have also been shown to promote aggregation of cockroaches. (Pennisi, 2016). It is hypothesized that all animals utilize microbes in communication, whether it be from bacteria cause body odor, in sweat, in feces, or otherwise.
Finally, microbes play a role in evolution of new species. Researchers were previously puzzled by the almost certain death of a hybrid parasitic wasp resulting from breeding of two-related species. The hybrids would die off leaving the two populations separated. Researchers found that antibiotic treated hybrid (killing off the microbes) survived and was actually hardier than its parent species. Thus, it appears that not only geographical separation, mutation and survival of the fittest play a role in evolution, but microbes may as well. (Arnold, 2014).
Almost all animals play the role of host to microbes. Thousands of microbes occupy every available and habitable space. In return, these microbes perform essential functions: protection from pathogens, process and digestion of food, influencing behavior and even shaping evolution.
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