Question

need help with this ..

From the pages 571-587 attached below.

1a) Suppose a population of guppies was infected with a parasite. In that population a mutation results in a parasite resistant genotype that spreads through the population through natural selection. A subsequent mutation in the parasite results in a genotype that is unaffected by the newly evolved resistant guppy genotype. What is the name of the hypothesis that explains this host parasite “arms race”.?

1b) What is this name based on?

2) In the guppy-parasite scenario described in question-1, why might the parasite be at an evolutionary advantage.

3) How do hosts overcome the disadvantage described in question-2?

Answer 1

ANSWER TO 1A-----This phenomenon is known as 'SEX AND RED QUEEN HYPOTHESIS' IN this process the red queen hypothesis explains that when a population is affected by a parasite, that particular population prefers sexual mode of reproduction over the asexual one. This is because we can have variation in sexual method and thus offspring produced have a chance of showing a gene resistant to parasite at any point in population. However in asexually produced offsprings the same set of genes are repeated. There can be a different set only with a chance of mutation. Thus the population can get off the parasite fast by sexual reproduction. That is why the population prefers it.

But, generally the rate of reproduction is higher in the parasites which are smaller than the hosts.

Suppose a asexual population is already parasite resistant and thus it has a better chance to survive if it keeps reproducing asexually. But the theory of natural selection will prevail in parasites and will force them to adapt a way to get through such disease resistant gene. Once the parasite is successful in overcoming the resistance they will spread throughout the population.

ANSWER TO 2-----------Thus there are much faster variations and mutations going on in the parasites and hence they easily adapt against the 'parasite resistant gene' of the host.. That is how parasites are at advantage in evolution.

ANSWER TO 1B----------The organism has to keep changing and adapting that is why it has been termed as Red queen Hypothesis because the queen of Lewis Carroll's story had to keep moving to be in place.

ANSWER TO 3----------Thus to keep up with the change the population shows sexual reproduction and with two different set of gamates, one from each parent has them a chance of possessing different genes. Moreover crossing over occurres in genes which gives even varied set. Apart from this processes like mutation and natural selection give way to the sexual reproducers. Thus there is a 'bet hedging process' which says that out of so many different offspring one offspring can be a lottery ticket and thus can fight the parasite as many times as it evovles.