In the arid southwest US, there are a number of populations that are found isola

Question

In the arid southwest US, there are a number of populations that are found isolated on “sky-islands" - the moist summits of high altitude mountains. These species cannot survive at lower altitudes where the climate is dryer and hotter. Their distributions may once have been connected but as the climate warmed and dried as the last ice age ended (about 18,000 years ago), the populations moved upwards in altitude and became isolated on the summits. A researcher studying a tree species isolated on the sky-islands measures HS = 0.15 and HT = 0.20 across the populations.

(a) Consider a pair of populations, each of size N = 8000 diploid individuals that split from a common ancestral population t generations ago. Assume there was no subsequent gene-flow between the populations after they split from each other. What equation describes the relationship between FST and the population split time?

(b) Use the equation in (a) to estimate the split time of the two populations, assuming that FST=0.25.

(c) If there had been gene flow between the two populations after they had split, do you think that your estimate of the split time computed in part (b) is older or younger than the true split time? Why?

(d) Can the investigator use FST alone to distinguish between the migration-drift equilibrium vs. complete isolation models described above? Explain.

just need help with part d and c

Explanation / Answer

c)

d)

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