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Discuss and explain Parasite - altered behaviour.

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Clare Johnson Queens College 17th October 2003 Discuss and explain Parasite - altered behaviour Parasitism is a symbiotic relationship between a parasite and host organism where the interaction benefits the parasite only. This is in contrast to mutualism where the parasite and host have mutual benefits. Often, the parasite is also harmful to the host by reducing its fitness, survival prospects and reproductive capability. However, this is not always the case with the host often being able to survive normally, once infected. The many advantages that parasitism offers to the parasite indicates that the interaction has been a form of evolutionary success with the host providing it with food, a stable physiochemical environment and its respiratory and metabolic needs. Parasite - altered behaviour is the phenomenon that a parasite is able to manipulate and modify its host's behaviour in order to benefit itself in terms of growth or transmission to the next host. Typically this occurs when the parasite has two hosts rather than one. The parasite must primarily attach to and infect its intermediate host but in order to complete its life cycle and reach full maturity it must reach its definite and final host. Parasite - altered behaviour is defined as the way in which the parasite manipulates the behaviour of its intermediate host in order to increase the host's susceptibility of predation and therefore the probability of transmission to a definitive host. ...read more.


Increased energy levels have also been shown to be the altered behaviour in parasite infected lemmings. When exploring, the infected lemmings with higher energy levels were more noticeable to their predators, the snowy owls which are the definite hosts of the protozoan parasite. The parasite infected lemmings also seemed to carry out less grooming which signifies reduced fear of their natural predators. As well as alterations to energy which increase levels, many instances have been found where the parasite benefits when it causes a reduction in its hosts energy levels. When ants where infected with parasites of cestodes and trematodes their behaviour in comparison to ants with no parasites was found to be much slower, sluggish or even stationary. This behaviour was seen to increase the chances of the ants being eaten by their predators which allowed the parasites to reach their definitive host and complete their life cycle. Activity levels can therefore be of benefit to the parasite in conjunction with predation where if they are decreased, a reduction in the stamina of the intermediate host increases the chance of predation and if they are increased, the animal becomes more noticeable and exposed which also increases chances of predation. Behaviour resulting in the intermediate host being more conspicuous to its predator can also be achieved in a number of ways other than altering activity levels. Parasite - altered behaviour may mean that the animal prefers higher places or swims closer to the surface and is therefore at a greater risk of being preyed upon. ...read more.


This is because some experiments have shown that altered behaviour of parasitised intermediate hosts has lead to predation by an animal other than the parasite's definitive host. Also, occasionally the altered behaviour seems to have no effect or may even be harmful to the parasite, sometimes benefiting the host to a greater degree. Some experiments have involved several altered behaviours and in these cases there is very little way of knowing to what extent each individual behavioural change contributes to benefiting the parasite. Despite the vast number of experiments which have been carried out, most experiments have been laboratory based with little thought to what would happen if the same situation occurred in the wild. Different methods have been used which means that many experiments are not suitable for comparative analysis. There is also a significant lack of statistical methods which have been used. Furthermore, hypothesises testing that parasite - altered behaviour is not advantageous to the parasite are rarely carried out which results in slightly biased and uncertain results. In conclusion, parasite - altered behaviour is the understanding that a parasite is able to modify the behaviour of its host in order to benefit itself which is often in conjunction with it reaching a second host. Many different ways in which this can be achieved have been illustrated through scientific experiments, however more extensive work needs to be carried out before we can be sure that the ultimate reason for parasite - altered behaviour is to benefit only the parasite. ...read more.

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