disruptive selection

Examples of disruptive selection in the following topics:

• Stabilizing, Directional, and Diversifying Selection

  • If natural selection favors an average phenotype by selecting against extreme variation, the population will undergo stabilizing selection.
  • Sometimes natural selection can select for two or more distinct phenotypes that each have their advantages.
  • Known as diversifying or disruptive selection, this is seen in many populations of animals that have multiple male mating strategies, such as lobsters.
  • Diversifying selection occurs when extreme values for a trait are favored over the intermediate values.This type of selection often drives speciation.
  • Different types of natural selection can impact the distribution of phenotypes within a population.In (a) stabilizing selection, an average phenotype is favored.In (b) directional selection, a change in the environment shifts the spectrum of phenotypes observed.In (c) diversifying selection, two or more extreme phenotypes are selected for, while the average phenotype is selected against.

• No Perfect Organism

  • Natural selection cannot create novel, perfect species because it only selects on existing variations in a population.
  • However, natural selection cannot produce the perfect organism.
  • Natural selection can only select on existing variation in the population; it cannot create anything from scratch.
  • Natural selection is also limited because it acts on the phenotypes of individuals, not alleles.
  • This a common example of disruptive selection.

• Choosing Team Size and Team Members

  • Membership in excess of twelve resulted in increased conflict and greater potential of subgroups forming that can disrupt team cohesion.
  • Individuals should be selected for teams so that as a whole the group has all the expertise needed to achieve its goals.

• Injuring the Plasma Membrane

  • Several types of antimicrobial drugs function by disrupting or injuring the plasma membrane.
  • The plasma membrane is selectively permeable to ions and organic molecules.
  • There are several types of antimicrobial drugs that function by disrupting or injuring the plasma membrane.
  • One example is daptomycin, a lipopeptide which has a distinct mechanism of action, disrupting multiple aspects of bacterial cell membrane function.
  • They disrupt the structure of the bacterial cell membrane by interacting with its phospholipids.

• Antibiotics and Selective Toxicity

  • Antibiotics are able to selectively target specific types of bacteria without harming the infected host.
  • He then proposed the idea that it might be possible to create chemicals that would act as a selective drug that would bind to and kill bacteria without harming the human host.
  • Common side-effects include diarrhea, resulting from disruption of the species composition in the intestinal flora, resulting, for example, in overgrowth of pathogenic bacteria, such as Clostridium difficile.
  • The remainder must be tested for their selective toxicities and therapeutic activities, and the best candidates can be examined and possibly modified.
  • In antibacterial production, microorganisms must be isolated, cultured, and tested for growth inhibition of target organisms and for their selective toxicity.

• Personal Biases

  • Biases seek to disrupt lucid contemplation of an issue by introducing externalities that are generally not relevant to the decision at hand.
  • Often times called selective search for evidence, confirmation bias occurs when decision makers seek out evidence that confirms their previously held beliefs, while discounting or diminishing the impact of evidence in support of differing conclusions.
  • Overconfidence bias: This is another potentially disruptive personal bias and occurs when a person subjectively overestimates the reliability of their judgments versus an objectively accurate outcome.

• Increasing Adaptation

  • Technological innovations, global market expansions, and the potential for constant (sometimes disruptive) innovation all point to the need for organizations to be adaptive.
  • Increasing an organization's ability to adapt to change and minimize disruption can reduce costs and save time.
  • Staff from different departments can be selected to form focus groups, where quality data can be collected.

• Genome Reduction

  • This process seems to be dominated by genetic drift resulting from small population size, low recombination rates, and high mutation rates, as opposed to selection for smaller genomes.
  • Some free-living marine bacterioplanktons also shows signs of genome reduction, which are hypothesized to be driven by natural selection.
  • This model illustrates four general features of reduced genomes and obligate intracellular species: ‘genome streamlining' resulting from relaxed selection on genes that are superfluous in the intracellular environment; a bias towards deletions (rather than insertions), which heavily affects genes that have been disrupted by accumulation of mutations (pseudogenes); very little or no capability for acquiring new DNA; and considerable reduction of effective population size in endosymbiotic populations, particularly in species that rely on vertical transmission.

• Antisense Agents

  • When this agent binds to the pathogen DNA or messenger RNA, the biosynthesis of target proteins is disrupted.
  • It prevents a pathogenic protein from being produced, rather than trying to selectively neutralize it once it is made.

• Antifungal Drugs

  • Amphotericin B is an example of a polyene antifungal; it is selective for ergosterol and can be used as a broad spectrum drug administered intravenously.
  • Squalene peroxidase is responsible for catalyzing the first step in ergosterol biosynthesis; inhibition of this enzyme results in disruption of ergosterol synthesis.
  • Caspofungin blocks cell-wall synthesis by disrupting glucan synthesis; it can target invasive candidiasis and aspergillus.