Extended Phenotype: The Long Reach Of The Gene

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Parasites are organisms that by design damage their hosts. Some have adapted to be able to alter their hosts for their benefit, such that the hosts that have been controlled by the parasite can be considered an extension of the parasites’ phenotype. Parasites have been observed to be able to change the morphology, development, biochemical and physical properties, behavior and diet of their host organism to suit its own needs. The parasites’ manipulation of the host has come to be known as the Extended Phenotype (the genes of one organism having observable effects in another organism in order to increase fitness). The benefit gained from this ability to control a host organism can only be explained by a carefully adapted trait in favor of the …show more content…
Dawkins talks about a common beaver and how its genes code for its fur, size, shape, diet and behavior. It is also noted that a beaver creates a dam to change the shallowness or depth of the water it inhabits in order to protect itself; the beaver creates the dam in order to ensure the continuation of its life cycle. In that way, from an evolutionary perspective the dam could be observed as an extension of the beavers’ phenotype. (Dawkins & Dennett 1999) In The Extended Phenotype: The Long Reach of the Gene, Dawkins wrote about shell thickness in a certain kind of snail that is host to a fluke parasite. The snails with thicker shells became host to this parasite because it served as adequate protection for the parasite, though along with the thicker shells came sterilization of the snails. The ability of the fluke parasite to rewire the snails’ investment in procreation to survival can, in fact support the observation that extra thickness in the snails’ shell due to the parasitic fluke is a beneficial adaptation of the …show more content…
The study used wild caught amphibians to ensure natural conditions and studied the parasite-induced defections in the frogs legs effecting locomotion after metamorphosis. Once the frogs were caught, swimming performance and endurance, jumping performance and foraging behavior were studied against non-infected frogs. Of the 114 frogs used in the performance trials, 63 were normal and 51 showed malformations and defects in normal functioning. The malformations were mainly in the hind/jumping legs and included having extra or less limbs than that of normal, non-infected frogs, see figure 1.1 showing a malformed parasite-infected frog exhibiting extra limbs. The malformed frogs showed considerably decreased functioning as compared to the non-infected frogs in that they had significantly diminished jumping distances of a 41% decrease, slower swimming speeds of a 37% decrease, decreased endurance of 66%, and a lower foraging success compared to frogs without malformations. These frogs also exhibited a 22% decrease in life span as well as a decrease in finding a reproductive mate. These findings show the ability of parasites to significantly alter host phenotypes, in this case physiologically, in order to successfully reach the end of their life cycle. (Goodman & Johnson
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