need help with these essay questions: 2.What role plays the tradeoff between con

Question

need help with these essay questions:

2.What role plays the tradeoff between consumption and virulence in the evolution of parasitic castrators?

3 Is castration and adaptive response of the parasite or the host (please, explain)?

5. What are the evolutionary consequences for parasitic castrators in terms of resource (host) monopolization / intraspecific competition for host individuals and resource (host) availability?

the link to the paper, please only use this paper to answer the q's outside info will not be given credit:

https://bb.clemson.edu/bbcswebdav/pid-2390923-dt-content-rid-22022896_2/courses/jbaezam-BIOL-3020/LaffertyKuris%28TrendsParasitlogy2009%29.pdf

Explanation / Answer

There are three main hypotheses about why a pathogen evolves as it does. These three models help to explain the life history strategies of parasites, including reproduction, migration within the host, virulence, etc. The three hypotheses are the Trade-Off Hypothesis, the Short-Sighted Evolution Hypothesis, and the Coincidental Evolution Hypothesis. All of these offer ultimate explanations for virulence in pathogens.

Trade-off hypothesis

At one time, some biologists argued that pathogens would tend to evolve toward ever decreasing virulence because the death of the host (or even serious disability) is ultimately harmful to the pathogen living inside. For example, if the host dies, the pathogen population inside may die out entirely. Therefore, it was believed that less virulent pathogens that allowed the host to move around and interact with other hosts should have greater success reproducing and dispersing.

But this is not necessarily the case. Pathogen strains that kill the host can increase in frequency as long as the pathogen can get transmited to a new host, whether before or after the host diesis irrespective. The evolution of virulence in pathogens is balanced between the costs and benefits of virulence to the pathogen. For example,the malarial parasite using a rodent and chicken model respectively and found that there was trade-off between transmission success and virulence as defined by host mortality.

Host susceptibility contributes to virulence. Once transmission occurs, the pathogen must ba able to establish an infection to continue. The more competent the host immune system is, the lesser the chance there is for the parasite to survive there. It may require multiple transmission events to find a suitably vulnerable host. During this time, the invader is dependent upon the survival of its current host. For this reason virulence thrives in a community with prevalent immune dysfunction and poor nutrition. Virulence weakens in a healthy population and as hosts acquire resistance. Good hygiene, nutrition and sanitation are all effective strategies against virulence.

For castrating parasites, the trade-off model has been modified to incorporate the parasite's capacity to convert host reproductive resources into transmission stages. These models predict that the optimal level of castration is total castration, but make no specific predictions for time to host death. Ebert et al. produced a verbal model to take into account that many castrators also induce enhanced growth of their hosts leading to gigantism. It was suggested that gigantism benefits the parasite, as it allows the storage of castration-liberated host resources into the host body mass until the parasite can make use of them as when required. The parasite may benefit from the larger host size as a bigger host provides more resources to the parasite. Castrating parasites usually have high resource demands, as they can reach considerable biomass (often 25% of host biomass) [15], which creates a strong negative correlation between parasite and host reproduction [14]. Premature host death would not allow efficient exploitation of the host, while postponing the killing of the host would result in diminished returns, as the growth trajectory of the host levels off with time. Analogous to the classical optimality models for virulence , a parasite inducing castration and gigantism should therefore show intermediate levels of virulence, where virulence is measured as time to host killing. The strong physiological trade-off between parasite reproduction and time to host death makes castrating parasites strong candidates to visualise the relationship between parasite fitness and virulence.

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