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Interdemic Group Selection with POPULUS

readings - introduction - exercise instructions - homework - instructor hints

Readings

OBrien, SJ and  Mayr, E. 1991. Bureaucratic Mischief - Recognizing endangered species and subspecies. Science
251: 1187-1188.

Werren, JH, Nur U, and Wu CI. 1988. Selfish genetic elements. Trends in Ecology & Evolution. 3: 297-302.

Dawkins, R.  The Blind Watchmaker. Genesmanship - Chapter 6.

Introduction for students

        Selection does not always occur at the individual level. In our readings this week, we reviewed several examples of selection at the level of individual genes (Werren et al. 1988) and at the level of kin groups (Dawkins).  In this POPULUS exercise we will explore a general model of group selection. Group selection has been controversial because it has been argued that traits don't evolve for "the good of the group" but only for "the good of the individual".

        This model of interdemic group selection presented by Levin and Kilmer in 1974 shows the feasibility of group selection. It assumes that a population is subdivided into separate, randomly interbreeding groups (called demes) that go extinct and then are re-established by random colonizers from pre-existing groups. Within each group, there is a locus polymorphic for an altruistic allele (A) and its non altruistic counterpart (E). This allele decreases the fitness of an individual carrying it, but it increases the survival probability of the group. Imagine that this allele codes for an alarm call or for not over-eating the resources available to each deme.

In this exercise we would like each of you to investigate how one of the following affects the spread of the altruistic allele:



Exercise instructions:




To access POPULUS:

Go to MODEL  --->  SELECTION MODELS  ---> GROUP SELECTION ---> INTERDEMIC SELECTION

Click "View" to see graphs. Change deme size,  population size, etc in the boxes in the lower half of the screen.

Homework

Graph your results and write a brief explanation of the outcome that you observe.

In light of your results, describe a potentially altruistic character in an organism (other than humans) that you know and discuss whether you think that this organism has the correct biological attributes to be affected by group selection or not.

Instructor hints

Populus versions can be downloaded from  http://www.cbs.umn.edu/populus/

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