Evolutionary pressure, selective pressure or selection pressure is exerted by factors that reduce or increase reproductive success in a portion of a population, driving natural selection.[1] It is a quantitative description of the amount of change occurring in processes investigated by evolutionary biology, but the formal concept is often extended to other areas of research.
It has been shown that putting an amino acid bio-synthesizing gene like HIS4 gene under amino acid selective pressure in yeast causes enhancement of expression of adjacent genes which is due to the transcriptional co-regulation of two adjacent genes in Eukaryota.[2]
Antibiotic resistance
Drug resistance in bacteria is an example of an outcome of natural selection. When a drug is used on a species of bacteria, those that cannot resist die and do not produce offspring, while those that survive potentially pass on the resistance gene to the next generation (vertical gene transmission). The resistance gene can also be passed on to one bacterium by another of a different species (horizontal gene transmission). Because of this, the drug resistance increases over generations. For example, in hospitals, environments are created where pathogens such as C. difficile have developed a resistance to antibiotics.[3] Antibiotic resistance is made worse by the misuse of antibiotics. Antibiotic resistance is encouraged when antibiotics are used to treat non-bacterial diseases, and when antibiotics are not used for the prescribed amount of time or in the prescribed dose.[4] Antibiotic resistance may arise out of standing genetic variation in a population or de novo mutations in the population. Either pathway could lead to antibiotic resistance, which may be a form of evolutionary rescue.[citation needed]
Nosocomial infections
Clostridioides difficile, gram-positive bacteria species that inhabits the gut of mammals, exemplifies one type of bacteria that is a major cause of death by nosocomial infections.[3]
When symbiotic gut flora populations are disrupted (e.g., by antibiotics), one becomes more vulnerable to pathogens. The rapid evolution of antibiotic resistance places an enormous selective pressure on the advantageous alleles of resistance passed down to future generations. The Red Queen hypothesis shows that the evolutionary arms race between pathogenic bacteria and humans is a constant battle for evolutionary advantages in outcompeting each other. The evolutionary arms race between the rapidly evolving virulence factors of the bacteria and the treatment practices of modern medicine requires evolutionary biologists to understand the mechanisms of resistance in these pathogenic bacteria, especially considering the growing number of infected hospitalized patients. The evolved virulence factors pose a threat to patients in hospitals, who are immunocompromised from illness or antibiotic treatment. Virulence factors are the characteristics that the evolved bacteria have developed to increase pathogenicity. One of the virulence factors of C. difficile that largely constitutes its resistance to antibiotics is its toxins: enterotoxin TcdA and cytotoxin TcdB.[5] Toxins produce spores that are difficult to inactivate and remove from the environment. This is especially true in hospitals where an infected patient's room may contain spores for up to 20 weeks.[6] Combating the threat of the rapid spread of CDIs is therefore dependent on hospital sanitation practices removing spores from the environment. A study published in the American Journal of Gastroenterology found that to control the spread of CDIs glove use, hand hygiene, disposable thermometers and disinfection of the environment are necessary practices in health facilities.[7] The virulence of this pathogen is remarkable and may take a radical change at sanitation approaches used in hospitals to control CDI outbreaks.[citation needed]
Just as with the development of antibiotic resistance in bacteria, resistance to pesticides and herbicides has begun to appear with commonly used agricultural chemicals. For example:
In the US, studies have shown that fruit flies that infest orange groves were becoming resistant to malathion, a pesticide used to kill them.
In Hawaii and Japan, the diamondback moth developed a resistance to Bacillus thuringiensis, which is used in several commercial crops including Bt corn, about three years after it began to be used heavily.
In England, rats in certain areas have developed such a strong resistance to rat poison that they can consume up to five times as much of it as normal rats without dying.
DDT is no longer effective in controlling mosquitoes that transmit malaria in some places, a fact that contributed to a resurgence of the disease.
In the southern United States, the weed Amaranthus palmeri, which interferes with production of cotton, has developed widespread resistance to the herbicide glyphosate.
In the Baltic Sea, decreases in salinity has encouraged the emergence of a new species of brown seaweed, Fucus radicans.[9]
Humans exerting evolutionary pressure
Human activity can lead to unintended changes in the environment. The human activity will have a possible negative effect on a certain population, causing many individuals from said population to die due to not being adapted to this new pressure. The individuals that are better adapted to this new pressure will survive and reproduce at a higher rate than those who are at a disadvantage. This occurs over many generations until the population as a whole is better adapted to the pressure.[1] This is natural selection at work, but the pressure is coming from man-made activity such as building roads or hunting.[10] This is seen in the below examples of cliff swallows and elk. However, not all human activity that causes an evolutionary pressure happens unintentionally. This is demonstrated in dog domestication and the subsequent selective breeding that resulted in the various breeds known today.
Rattlesnakes
In more heavily (human) populated and trafficked areas, reports have been increasing of rattlesnakes that do not rattle. This phenomenon is commonly attributed to selective pressure by humans, who often kill the snakes when they are discovered.[11] Non-rattling snakes are more likely to go unnoticed, so survive to reproduce offspring that, like themselves, are less likely to rattle.[citation needed]
Cliff swallows
Populations of cliff swallows in Nebraska have displayed morphological changes in their wings after many years of living next to roads.[10] Collecting data for over 30 years, researchers noticed a decline in wingspan of living swallow populations, while also noting a decrease in the number of cliff swallows killed by passing cars. Those cliff swallows that were killed by passing cars showed a larger wingspan than the population as a whole. Confounding effects such as road usage, car size, and population size were shown to have no impact on the study.
Elk
Evolutionary pressure imposed by humans is also seen in elk populations.[12] These studies do not look at morphological differences, but behavioral differences. Faster and more mobile male elk were shown to be more likely to fall prey to hunters. The hunters create an environment where the more active animals are more likely to succumb to predation than less active animals.[4] Female elk who survived past two years, would decrease their activity as each year passed, leaving more shy female elk that were more likely to survive.[12] Female elk in a separate study also showed behavioral differences, with older females displaying the timid behavior that one would expect from this selection.[13]
Dog domestication
Since the domestication of dogs, they have evolved alongside humans due to pressure from humans and the environment.[6] This began by humans and wolves sharing the same area, with a pressure to coexist eventually leading to their domestication. Evolutionary pressure from humans led to many different breeds that paralleled the needs of the time, whether it was a need for protecting livestock or assisting in the hunt.[7] Hunting and herding were a couple of the first reasons for humans artificially selecting for traits they deemed beneficial.[8] This selective breeding does not stop there, but extends to humans selecting for certain traits deemed desirable in their domesticated dogs, such as size and color, even if they are not necessarily beneficial to the human in a tangible way.[9] An unintended consequence of this selection is that domesticated dogs also tend to have heritable diseases depending on what specific breed they encompass.[14]
1 2 Ostrander, Elaine A; Galibert, Francis; Patterson, Donald F (2000-03-01). "Canine genetics comes of age". Trends in Genetics. 16 (3): 117–124. doi:10.1016/S0168-9525(99)01958-7. PMID10689352.
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of such infections. They may either kill or inhibit the growth of bacteria. A limited number of antibiotics also possess antiprotozoal activity. Antibiotics are not effective against viruses such as the ones which cause the common cold or influenza. Drugs which inhibit growth of viruses are termed antiviral drugs or antivirals. Antibiotics are also not effective against fungi. Drugs which inhibit growth of fungi are called antifungal drugs.
Antimicrobial resistance occurs when microbes evolve mechanisms that protect them from antimicrobials, which are drugs used to treat infections. This resistance affects all classes of microbes, including bacteria, viruses, protozoa, and fungi. Together, these adaptations fall under the AMR umbrella, posing significant challenges to healthcare worldwide. Misuse and improper management of antimicrobials are primary drivers of this resistance, though it can also occur naturally through genetic mutations and the spread of resistant genes.
Staphylococcus aureus is a gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive for catalase and nitrate reduction and is a facultative anaerobe, meaning that it can grow without oxygen. Although S. aureus usually acts as a commensal of the human microbiota, it can also become an opportunistic pathogen, being a common cause of skin infections including abscesses, respiratory infections such as sinusitis, and food poisoning. Pathogenic strains often promote infections by producing virulence factors such as potent protein toxins, and the expression of a cell-surface protein that binds and inactivates antibodies. S. aureus is one of the leading pathogens for deaths associated with antimicrobial resistance and the emergence of antibiotic-resistant strains, such as methicillin-resistant S. aureus (MRSA). The bacterium is a worldwide problem in clinical medicine. Despite much research and development, no vaccine for S. aureus has been approved.
A prophage is a bacteriophage genome that is integrated into the circular bacterial chromosome or exists as an extrachromosomal plasmid within the bacterial cell. Integration of prophages into the bacterial host is the characteristic step of the lysogenic cycle of temperate phages. Prophages remain latent in the genome through multiple cell divisions until activation by an external factor, such as UV light, leading to production of new phage particles that will lyse the cell and spread. As ubiquitous mobile genetic elements, prophages play important roles in bacterial genetics and evolution, such as in the acquisition of virulence factors.
Virulence is a pathogen's or microorganism's ability to cause damage to a host.
Evolutionary biology is the subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth. It is also defined as the study of the history of life forms on Earth. Evolution holds that all species are related and gradually change over generations. In a population, the genetic variations affect the phenotypes of an organism. These changes in the phenotypes will be an advantage to some organisms, which will then be passed on to their offspring. Some examples of evolution in species over many generations are the peppered moth and flightless birds. In the 1930s, the discipline of evolutionary biology emerged through what Julian Huxley called the modern synthesis of understanding, from previously unrelated fields of biological research, such as genetics and ecology, systematics, and paleontology.
Clostridioides difficile infection, also known as Clostridium difficile infection, is a symptomatic infection due to the spore-forming bacterium Clostridioides difficile. Symptoms include watery diarrhea, fever, nausea, and abdominal pain. It makes up about 20% of cases of antibiotic-associated diarrhea. Antibiotics can contribute to detrimental changes in gut microbiota; specifically, they decrease short-chain fatty acid absorption which results in osmotic, or watery, diarrhea. Complications may include pseudomembranous colitis, toxic megacolon, perforation of the colon, and sepsis.
Serial passage is the process of growing bacteria or a virus in iterations. For instance, a virus may be grown in one environment, and then a portion of that virus population can be removed and put into a new environment. This process is repeated with as many stages as desired, and then the final product is studied, often in comparison with the original virus.
The Clostridia are a highly polyphyletic class of Bacillota, including Clostridium and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them. Species of the class Clostridia are often but not always Gram-positive and have the ability to form spores. Studies show they are not a monophyletic group, and their relationships are not entirely certain. Currently, most are placed in a single order called Clostridiales, but this is not a natural group and is likely to be redefined in the future.
Paul W. Ewald is an American evolutionary biologist, specializing in the evolutionary ecology of parasitism, evolutionary medicine, agonistic behavior, and pollination biology. He is the author of Evolution of Infectious Disease (1994) and Plague Time: The New Germ Theory of Disease (2002), and is currently director of the program in Evolutionary Medicine at the Biology Department of the University of Louisville.
The domestication of vertebrates is the mutual relationship between vertebrate animals including birds and mammals, and the humans who have influence on their care and reproduction.
Bacteria are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of dead bodies; bacteria are responsible for the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Bacteria also live in mutualistic, commensal and parasitic relationships with plants and animals. Most bacteria have not been characterised and there are many species that cannot be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.
Host–parasite coevolution is a special case of coevolution, where a host and a parasite continually adapt to each other. This can create an evolutionary arms race between them. A more benign possibility is of an evolutionary trade-off between transmission and virulence in the parasite, as if it kills its host too quickly, the parasite will not be able to reproduce either. Another theory, the Red Queen hypothesis, proposes that since both host and parasite have to keep on evolving to keep up with each other, and since sexual reproduction continually creates new combinations of genes, parasitism favours sexual reproduction in the host.
Evolutionary biology, in particular the understanding of how organisms evolve through natural selection, is an area of science with many practical applications. Creationists often claim that the theory of evolution lacks any practical applications; however, this claim has been refuted by scientists.
In biology, a pathogen, in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.
Clostridioides difficile is a bacterium known for causing serious diarrheal infections, and may also cause colon cancer. It is known also as C. difficile, or C. diff, and is a Gram-positive species of spore-forming bacteria. Clostridioides spp. are anaerobic, motile bacteria, ubiquitous in nature and especially prevalent in soil. Its vegetative cells are rod-shaped, pleomorphic, and occur in pairs or short chains. Under the microscope, they appear as long, irregular cells with a bulge at their terminal ends. Under Gram staining, C. difficile cells are Gram-positive and show optimum growth on blood agar at human body temperatures in the absence of oxygen. C. difficile is catalase- and superoxide dismutase-negative, and produces up to three types of toxins: enterotoxin A, cytotoxin B and Clostridioides difficile transferase. Under stress conditions, the bacteria produce spores that are able to tolerate extreme conditions that the active bacteria cannot tolerate.
ESKAPE is an acronym comprising the scientific names of six highly virulent and antibiotic resistant bacterial pathogens including: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. The acronym is sometimes extended to ESKAPEE to include Escherichia coli. This group of Gram-positive and Gram-negative bacteria can evade or 'escape' commonly used antibiotics due to their increasing multi-drug resistance (MDR). As a result, throughout the world, they are the major cause of life-threatening nosocomial or hospital-acquired infections in immunocompromised and critically ill patients who are most at risk. P. aeruginosa and S. aureus are some of the most ubiquitous pathogens in biofilms found in healthcare. P. aeruginosa is a Gram-negative, rod-shaped bacterium, commonly found in the gut flora, soil, and water that can be spread directly or indirectly to patients in healthcare settings. The pathogen can also be spread in other locations through contamination, including surfaces, equipment, and hands. The opportunistic pathogen can cause hospitalized patients to have infections in the lungs, blood, urinary tract, and in other body regions after surgery. S. aureus is a Gram-positive, cocci-shaped bacterium, residing in the environment and on the skin and nose of many healthy individuals. The bacterium can cause skin and bone infections, pneumonia, and other types of potentially serious infections if it enters the body. S. aureus has also gained resistance to many antibiotic treatments, making healing difficult. Because of natural and unnatural selective pressures and factors, antibiotic resistance in bacteria usually emerges through genetic mutation or acquires antibiotic-resistant genes (ARGs) through horizontal gene transfer - a genetic exchange process by which antibiotic resistance can spread.
Recent human evolution refers to evolutionary adaptation, sexual and natural selection, and genetic drift within Homo sapiens populations, since their separation and dispersal in the Middle Paleolithic about 50,000 years ago. Contrary to popular belief, not only are humans still evolving, their evolution since the dawn of agriculture is faster than ever before. It has been proposed that human culture acts as a selective force in human evolution and has accelerated it; however, this is disputed. With a sufficiently large data set and modern research methods, scientists can study the changes in the frequency of an allele occurring in a tiny subset of the population over a single lifetime, the shortest meaningful time scale in evolution. Comparing a given gene with that of other species enables geneticists to determine whether it is rapidly evolving in humans alone. For example, while human DNA is on average 98% identical to chimp DNA, the so-called Human Accelerated Region 1 (HAR1), involved in the development of the brain, is only 85% similar.
Wild ancestors are the original species from which domesticated plants and animals are derived. Examples include dogs which are derived from wolves and flax which is derived from Linum bienne. In most cases the wild ancestor species still exists, but some domesticated species, such as camels, have no surviving wild relatives. In many cases there is considerable debate in the scientific community about the identity of the wild ancestor or ancestors, as the process of domestication involves natural selection, artificial selection, and hybridization.
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