Exam 20: Evolution and Medicine

Imagine two populations of snails that are polymorphic for sexual reproduction.In each of the two populations,several asexual lineages and a panmictic,sexually reproducing subpopulation of snails are living in the same environment.Several years ago,a new pathogen was detected in the first population.This pathogen is transmitted predominantly between parents and their offspring,but on occasion,it is also transmitted horizontally between unrelated individuals.The pathogen is now infecting both sexual and asexual individuals.Since the introduction of the pathogen,the formerly stable ratio of sexual to asexual snails has shifted significantly in favor of the sexually reproducing individuals.At the same time,the second population became infected with a pathogen that is almost always transmitted horizontally.In the second population,no shift in the ratio of sexuals to asexuals has been observed.Speculate on why the difference in transmission between the two pathogens may have shifted the proportion of sexual reproduction in the first but not in the second population.Limit your answer to one or two sentences.

What two main factors are responsible for the asymmetry in the coevolutionary arms race between microbial pathogens and their multicellular hosts?

Why is there no lifelong vaccine protection against flu as there is by a measles vaccine?

Ask a question about fever at each of Tinbergen's four levels (1,2,3,and 4)of explanation.Limit your answer to one sentence for each level.

Figures A and B show the effect of an early- and a late-acting mutation on the lifetime fitness of individuals.Based on the graphs,how would you determine which of the two mutations had a greater effect on lifetime fitness? Limit your answer to one sentence.

What is the likely phylogenetic explanation for the crossing of food and air pathways in humans?

Patients with severe bacterial sepsis who develop a fever have higher survival rates than those who do not develop a fever.Does this observation provide causative evidence for the beneficial role of fever in fighting infections?

Which of the two viral phylogenies below shows the signature of a recent,rapid population expansion? Justify your answer in one or two sentences.

The figure below shows the effect of an antagonistic pleiotropic mutation (A).What would be the effect of a mutation (B)that delayed the onset of reproduction without changing the survival curve?

.Ackermann and colleagues (2003)investigated senescence in bacteria.What do the following results demonstrate and why are they surprising given evolutionary theory on aging?

Which part of the immune system's "learning system" is responsible for maintaining life-long immunity against measles after a measles infection?

Which of the following are strategies with which vertebrate hosts counteract the asymmetries between most pathogens and their hosts?

Name three methods that pathogens use to subvert their host's immune system.

Under which of the following evolutionary explanations for disease does the antagonistic pleiotropy hypothesis for aging fall?

Which of the following hypothetical viruses would likely show a "cactus-shaped" population phylogeny?

Can you think of examples,similar to the crossing pathways of food and air,in human anatomy or physiology that represent an "imperfect design" due to evolutionary history?

Under which hypothesis may pathogens ultimately be responsible for the evolution of sexual reproduction in multicellular organisms?

Individuals of a certain tree species experience a markedly higher mortality rate at age 200 and beyond.Name two other changes you would expect in 200-year-old trees if this increase in mortality was accompanied by senescence.

Which of the following represents a similarity between the evolution of tumors and the vertebrate immune response?

Many wild mushrooms make delicious food,but some are highly toxic and can result in a fatal meal.Apply the principle of asymmetric harm to mushroom identification,and recommend a strategy for mushroom identifiers.