Week 1 - Introduction to evolution Flashcards
What is a parasite
A parasite is a small replicator taking advantage of usually a larger host causing harm to the host. Viruses, bacteria, protozoans and helminths are typical parasites
What is virulence
Virulence is the harm a parasite causes to its host. Infected hosts suffer from morbidity and mortality including reduced life-span, fecundity reduction, reduced mating success and other forms of physiological harm. The expression of virulence is plastic and often depends on environmental conditions which can evolve rapidly. It can vary from host to host and parasite to parasite while also being influenced by the host-parasite interaction; the combination of host and parasite genotypes plays a role in the expression of virulence.
What is specificity?
Parasites are generally host specific, with some parasites having evolved specific mechanisms of transmission and virulence to survive in their hosts. Specificity can be defined as the variation among host species in their performance against exposure to a parasite. Specificity is usually used in descriptive contents. Its a soft concept with no definitive answer to what the host range of a parasite is. An example of specificity is with Plasmodium spp. and which primates host species can be infected
What are symbiots and symbiosis?
This is related to the function of the parasite and whether it is harmful or beneficial. The symbiot refers to the parasite. The relationship is either one of parasitism which is harmful to the host, like HIV. Or it can be symbiotic or mutualist where there are shared benefits to the interaction like with clown fish and anemones.
What are micro- and macro-parasites? Does it apply to all parasites?
The key difference between micro and macro parasites are the different states of the hosts. With microparasites hosts can have two to three states; susceptible or naive, infected and recovered hosts. This usually applies to bacteria and viruses. Macroparasites are classed by how many parasites a host has, like with anthropods and helminths. This classification doesn’t apply universally, with exceptions for fungal infections and mosquito vectored infections.
What is meant by transmission?
Transmission is the passing of a symbiot from an infected host to another host. Generally there are two modes of transmission; vertical tranmission from parents to offsprings and horizontal transmission among unrelated hosts with the possibility of mixed-mode transmission. There are also many classification of route of transmission including waterborne, vectorborne and sexual transmission
What is density dependent transmission?
DDT is transmission that is dependent on the density of the host population. This has the potential to regulate host populations whereby the higher the density, the more transmission there is and the stronger the effect of the parasite on the population. This regulatory power is believed to be a major structuring force in biodiversity
What is mass action principle?
The principle assumes that the spread of a parasite is proportional to the product of the density of sucueptible hosts times the density of he infectious hosts. Where S is the number of susceptible hosts and I is the number of infected hosts (therefore S + I = N, total host population) it states that the spread of the disease is proportional to SI. Where B is the tempotal element for real-time transmission, BSI is the total number of new infection per unit of time for a horizontally transmitted disease.
What is evolution?
Evolution are the genetic changes in the composition of a population over time. It is visible as changes within a population over time or as a divergence among population across space
What is micro- and macro-evolution?
Microevolution is the change in allele frequencies that occurs over time within a population. This change is due to four different processes: mutation, selection, gene flow and genetic drift. This change happens over a relatively short amount of time compared to the changes termed macroevolution. Macroevolution refers to evolution of groups larger than an individual, it focuses on the differences visible at or above the species level
What is genetic drift? what are the consequences?
Genetic drift are the chance events of the sampling effect when genes are passed on from parent to offspring. They can lead to unequal representation of allelic variations in the next generation. Normally, changes caused by genetic drift are small and take a long time to create substantial changes. Genetic drift may cause gene variants to disappear completely and thereby reduce genetic variation. An extreme form of GD is population bottleneck
What is a mutation?
A mutation is a change to the gene’s DNA sequence to produce something different. Mutations are important source of genetic novelty manifesting as point mutations, gene deletions, gene duplications etc. Mutation rates need to be scaled e.g. per base per generation and greatly vary across organisms e.g. RNA viruses have high mutation rates
What is gene flow? what are the consequences?
Gene flow is the movement or introduction of genetic variants into populations. Its the result of organisms moving among and between populations through dispersal or migration. A consequence of gene flow within a population is it can introduce or reintroduce alleles and increase genetic variation. However, between populations, gene flow can make distant populations more homogenous therefore reducing population divergence.
What is genetic recombination?
The process of mixing, or recombining the genomes of two individuals. Recombination may create and destroy favourable allele combinations between loci while segregation acts the same at the locus
Why are parasites notorious for their high rates of adaptive evolution?
They have high rates of mutation rates e.g. retroviruses have a large population size with large absolute numbers of mutations and genetic material is varied through genetic recombination including horiztonal gene transfer. In the case of haploid organisms, every mutation is dominant on its single chromosome too. These factors make them fast evolvers and highly adaptable.
