Background:

You are a CDC (Center for Disease Control) researcher studyingmalaria. Your goal is to understand the evolution of malaria inorder to be able to possibly predict where a future outbreak maybe. To do this you will be using information from the evolution ofthe pathogen, the host, and changes in the environment. Topics tothink about include:

• What is the evolutionary origin of human malaria? (hint: thinkabout host-pathogen cospeciation or host shift)
  • What could you learn about the adaptability of the malariapathogen based on its reconstructed evolutionary history?
• How does the information on the origin of human malaria affectyour prediction for possible outbreaks? (hint: think what are thereservoirs for malaria pathogens)
• What would happen if changes in climate affect the distributionof the malaria mosquito vector?
  • Think if and how patterns of malaria geographic distributionwould change by considering also the effect that thepresence/absence of the sickle cell anemia allele would play
  • How likely is it that human populations living in a geographicarea without malaria will have a high frequency of the sickle cellanemia allele?

The information that you have is:

• Knowledge of the malaria cycle, which includes one host,primate (human, chimpanzee, or gorilla), and one vector, mosquito.Malaria is prevalent in areas where the mosquitoes thrive (hot andhumid).
• Access to three different pathogens: Plasmodiumfalciparum (host: human), P. reichenowi (host:chimpanzee), Plasmodium sp. (host: gorilla).
• The knowledge that individuals that have one (heterozygotes) ortwo (homozygote recessive) alleles for sickle cell are partiallyprotected from malaria (although they still suffer some negativeeffects from the sickle cell disease)

Think about what type of information you would need to approachthe problem above and how you would interpret different patterns.Answer the questions with a series of “if-then” scenarios in whichyou explore a different types of information you may get from thedata and how you would interpret it.

Malaria life cycle

Question:

How would you distinguish between cospeciation and host shift(draw phylogenetic trees with the malaria pathogens and their hoststo illustrate the two scenarios)? Briefly describe and explain yourphylogenies.