A study of the evolution of the antagonist

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A study of the evolution of the antagonist

Overview[ edit ] Hosts and parasites exert reciprocal selective pressures on each other, which may lead to rapid reciprocal adaptation. For organisms with short generation times, host—parasite coevolution can be observed in comparatively small time periods, making it possible to study evolutionary change in real-time under both field and laboratory conditions.

These interactions may thus serve as a counter-example to the common notion that evolution can only be detected across extended time. Major diseases such as malariaAIDS and influenza are caused by coevolving parasites.

Better understanding of coevolutionary adaptations between parasite attack strategies and host immune systems may assist in the development of novel medications and vaccines. These changes may be determined by three main types of selection dynamics.

For example, the parasite should adapt to the most common host genotypebecause it can then infect a large number of hosts. In turn, a rare host genotype may then be favored by selection, its frequency will increase and eventually it becomes common.

Subsequently, the parasite should adapt to the former infrequent genotype. This selection mode is expected for multicellular hosts, because adaptations can occur without the need for novel advantageous mutationswhich are less likely to be frequent in these hosts because of relatively small population sizes and relatively long generation times.

It is due to a mutation in the hemoglobin gene leading to sickle shape formation of red blood cells, causing clotting in blood vessels, restricted blood flow, and reduced oxygen transport.

At the same time, the mutation confers resistance to malariacaused by Plasmodium parasites, which are passed off in red blood cells after transmission to humans by mosquitoes.

Hence, homozygote and heterozygote genotypes for the sickle-cell disease allele show malaria resistance, while the homozygote suffers from severe disease phenotype. The alternative homozygote, which does not carry the sickle cell disease allele, is susceptible to infection by Plasmodium.

As a consequence, the heterozygote genotype is selectively favored in areas with a high incidence of malaria. Selective sweeps are one form of directional selection, where the increase in frequency will eventually lead to the fixation of the advantageous allele.

The process is considered to be slower in comparison to negative frequency dependent selection. It may produce an "arms race", consisting of the repeated origin and fixation of new parasite virulence and host defence traits.

Thus genotype-by-genotype-by-environment G x G x E interactions affect fitness of the antagonists. In other words, the specific environmental conditions determine how any genotype of one species influences the fitness of another species. These hotspots are intermixed with so-called coldspots in which only one or neither species adapts to the antagonist.

This remixing determines the exact dynamics of the geographic mosaic by shifting the spatial distributions of potentially coevolving alleles and traits.

Among plants, Plantago lanceolata and its parasite the powdery mildew Podosphaera plantaginis have been intensively studied on the Aland islands in south-western Finland. There are more than host populations in this region, where both populations can evolve freely, in absence of human-imposed selection, in a heterogeneous landscape.

Both partners can reproduce asexually or sexually. The system has spatially divergent coevolutionary dynamics across two metapopulations as predicted by the mosaic theory. The New Zealand freshwater snail Potamopyrgus antipodarum and its different trematode parasites represent a rather special model system.

There is a high correlation between the presence of parasites and the frequency of sexual individuals within the different populations. This result is consistent with the Red Queen hypothesis that sexual reproduction is favoured during host—parasite coevolution.

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Trade-off between transmission and virulence[ edit ] Tribolium castaneum Tribolium castaneumthe red flour beetle, is a host for the microsporidian Nosema whitei. In turn, parasite fitness most likely depends on a trade-off between transmission spore load and virulence. Therefore, investment in one trait e.

Moreover, genes are often pleiotropichaving multiple effects. Thus, a change in a pleiotropic immunity or virulence gene can automatically affect other traits. There is thus a trade-off between benefits and costs of the adaptive changes that may prevent the host population from becoming fully resistant or the parasite population from being highly pathogenic.

The costs of gene pleiotropy have been investigated in coevolving Escherichia coli and bacteriophages.

A study of the evolution of the antagonist

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