Last winter semseter, I took an undergraduate biological anthropology class focused on nutrition and evolution, where we learned about sickle cell anemia. Though we discussed the condition from an evolutionary anthropology perspective, I found that the example is very relevant to the concepts we’ve been talking about in class, especially species interactions and evolution by natural selection.
Basically, sickle cell anemia is a disease that causes red blood cells to be shaped like sickles (long and curved), which causes health complications and lowers life expectancy for those who have two alleles for sickle cell anemia. However, if an individual only has one mutated allele for sickle cell, he or she actually has a higher resistance against malaria. Accordingly, the mutation has a higher prevalence in people from tropical and subtropical areas, where resistance to malaria can improve chances of survival.
This relates to what we have been disusing in class because it is an example of interactions between species (a +/- predation relationship) and how these interactions can influence evolution of prey defenses. Humans (prey) evolved defenses against the predator (malaria) with a mutated allele that improves immunity against malaria. Interestingly, even though two alleles for sickle cell anemia can cause severe health problems and decreased fitness, natural selection still favors the allele since those who only have one are better able to evade malaria predators and survive to pass the gene on to their descendants.
*Information synthesized from Wikipedia page (http://en.wikipedia.org/wiki/Sickle-cell_disease) and U of M Professor A. Roberto Frisancho’s lecture notes from Anthrobio 364, Winter Semester 2009
Starfish as keystone predators: The following link shows a timelapse video of a starfish feeding on a mussel, similar to what Dr. Allen told us about in class. The video will only play with Quicktime…can't figure out another way to get it to work so sorry if you have to install a plug-in to see it.