XIX.6 Parasites often facilitate their propagation by specific interventions in the physiological, ecological and ethological traits of the host organism

The fact that a parasite is frequently in close contact with its host provides it with an opportunity for targeted interventions in the functioning of the host organism.Parasites are capable of modifying for their needs various traits of the host, from the morphology through regulation of metabolism andallocation of energy for the individual life functions to specific interventions in the nervous system, leading to changes in the behavior of the host.Thus, parasites are typical organisms utilizing the extended phenotype principle (Dawkins 1982)(see XVIII.6).A number of their genes have become fixed in evolution, not because they would favorably affect the traits of the parasite organism, but because, through their products, they affect the traits of the host organism.Thus, the body of the host becomes part of the extended phenotype of the parasite and a great many of its traits assist not in spreading its own genes but rather in spreading the genes of the parasite.The genes of the parasite and genes of the host frequently have quite opposing interests in relation to the traits and functioning of the host organism.As was mentioned in Section XIX.2, the genes of a parasite in the co-evolutionary battle with the genes of the host are in a more advantageous position, so that their interests frequently predominate in the attacked organism.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.