I. For a group of subpopulations of grizzly bears, an F ST value of 0.18 is calc
ID: 212303 • Letter: I
Question
I. For a group of subpopulations of grizzly bears, an FST value of 0.18 is calculated based on data from several microsatellite loci.
A). From this value, provide an indirect estimate of the number of migrants that travel between the populations each generation.
B). What assumptions are you making in inferring this estimate of the number of migrants per generation (hint: what theoretical model is this method of estimation based on)?
C). Using information on heterozygosity, the effective population size of each population is estimated to be about 1,000. Calculate the migration rate
D). Although the effective population size is 1000, mark recapture experiments estimate that there are approximately 5,000 bears in each population. In a short paragraph, describe two factors that are likely to reduce the effective population size of the bear population relative to the census count.
Explanation / Answer
C) FST uses SNP and microsatellite data to calculate the population difference due to genetic structure.
FST = 1 / (1+4Nm)
Where N is the population size and m is the rate of migration between different populations.
Effective population size is = 1000 and
FST = 0.18
Hence,
0.18= 1 / (1+4*1000*m)
0.18 + m (720) = 1
m = 0.0011
Migration rate is 0.0011
A) Then number of migrants that travel between population is -
1000 * 0.0011 = 1.13
B) The estimation is based on island model of population structure by Seawall Wright, which shows an direct relationship between FST and the migration rate.
D) The effective population size of bears is 1000 but the census count shows that there are approximately 5000 bears in each population, which creates a 5 fold discrepancy between the two.
Multiple factors can lead to this reduction of effective population size, such as-
1. Selection:
Liu and Mittler, 2008 (doi: 10.1186/1471-2148-8-133) showed that selection can lead to dramatic decrease in the effective population size. So selection can act as one factor.
2. Mutation and recombination can also alter the allele frequency leading to a decrease in the effective population size.