Evolution, 4th Edition

(Amelia) #1
B. Charlesworth and colleagues review the ef-
fects of gene flow and other evolutionary
forces on patterns of neutral variation in DNA
in “The effects of genetic and geographic
structure on neutral variation” (Ann. Rev. Ecol.
Evol. Syst. 34: 99–125, 2003). DNA sequences
are widely used to study the genetic structure
of populations; see “inference of population
structure using multilocus genotype data:
linked loci and correlated allele frequencies”
by D. falush and colleagues (Genetics 164:
1567–1587, 2003).

There is a growing literature on how species
ranges evolve, and specifically how they are
responding to climate change. Two authori-
tative overviews are “Ecological and evolu-
tionary responses to recent climate change”
by C. Parmesan (Ann. Rev. Ecol. Evol. Syst.
37: 637–669, 2006) and “Evolution and ecol-
ogy of species range limits” by J. P. Sexton
and colleagues (Ann. Rev. Ecol. Evol. Syst. 40:
415–436, 2009).

PRoBlEMS AND DiSCuSSioN ToPiCS



  1. Suppose that in generation 0, the frequency of
    allele A 1 in a population of armadillos is 0.4. in
    each generation, 10 percent of the individuals
    in that population are migrants from another
    population that has an allele frequency of 0.6.
    a. Calculate the frequency of A 1 in each of the
    next two generations (generations 1 and 2).
    b. is the change in allele frequency in genera-
    tion 2 greater than, less than, or equal to the
    change in generation 1? How can you explain
    that answer?
    c. What will the allele frequency become in this
    population after many generations?

  2. Consider a cricket that has recently colonized a
    remote oceanic island from a source population
    on a continent. How do you expect the average
    size of wings in the island population to compare
    with the average size on the continent? How
    do you expect wing size in the island popula-
    tion to evolve over the next several hundred
    generations?

  3. Equation 8.4 gives the equilibrium value of FST
    between two populations for a neutrally evolv-
    ing locus when the populations are of equal size
    and are exchanging equal numbers of migrants.
    When there is symmetrical migration among a
    large number of populations, a different equa-
    tion holds: FST = 1 / (1 + 4 Ne m). Suppose you
    sample individuals from two populations, but
    you do not know whether these populations
    exchange migrants only with one another, or
    whether they are part of a group of many popu-
    lations that exchange migrants. you genotype
    the individuals in your samples at several loci
    and find that the average FST between the two


populations is 0.25. using the equation given
above and Equation 8.4, determine the range of
plausible values for the number of migrants that
arrive in each population in each generation.


  1. Clines in body size have been observed in many
    species, such as the latitudinal cline in moose
    shown in figure 8.2.
    a. Does a cline in body size necessarily result
    from variation in allele frequencies at loci that
    affect body size? Why or why not?
    b. How might you determine whether a cline
    in body size was caused by clines in allele
    frequencies?
    c. Say there is strong evidence that a latitudinal
    cline in body size in a squirrel is caused by
    variation in allele frequencies. Do you think
    that data showing how rapidly the average
    body size changes with latitude could by
    themselves be used to determine how selec-
    tion varies in space? Why or why not?

  2. A species that has a high rate of long-distance
    dispersal is more likely to colonize new habitat.
    But that species may also be less likely to adapt
    to local conditions, because migration will be
    stronger than local selection pressures for many
    loci. in light of those considerations, when do
    you expect that increasing dispersal might result
    in the evolution of a larger geographic range,
    and when might it not?

  3. it is now common to score many thousands of
    SNPs in numerous individuals sampled from sev-
    eral populations. (See, for example, the results
    from stickleback fishes shown in figure 8.8).
    Many of these SNPs are neutral and therefore


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