Week 7: Multiple Population Genetics: Dispersal and Gene Flow Flashcards
What does gene flow depend on?
reproduction occurring
What is dispersal?
the movement of individuals between populatinos
What is migration?
periodic movements between specific geographic areas
In what 3 ways can we infer dispersal from genetics?
- Genetic differences between populations
- Population assignment tests
- Landscape Genetics
What methods can we use to measure dispersal/migration without genetics?
- movement ecology (GPS)
- Mark-recapture
What facilitates dispersal of individuals?
- moving by themselves
- wind
- ocean currents
What main factor influences genetic differentiation between populations?
gene flow
What forces reduce genetic diversity in a population?
- genetic drift and inbreeding
- caused by barriers between populations, small population sizze
What 3 levels are F statistics measured at?
- Fis = degree of inbreeding within a population (same as F/ INBREEDING COEFF)
- Fst = genetic differentiation between subpopulation (FIXATION INDEX)
- Fit = degree of inbreeding compared to all subpops (not as useful)
How do we calculate Fst?
Fst = (Ht-Hs)/Ht
Ht = expected total heterozygosity
Hs = expected subpop heterozygosity
Fst=0 –> no differentiation
Fst=1 –> complete differentiation
How do we calculate total expected heterozygosity (Ht) for finding Fst values?
Ht = He = (2pq)
- find allele frequencies and calculate 2pq
How do we find a subpopulation expected heterozygosity (Hs) for finding Fst values?
Hs = He (2piqi)
- Find 2pq for each subpopulation separately
- average 2pq between the two populations
What do we assume about subpopulations?
that there is a mutation-drift equilibrium
What data could challenge the assumption of a mutation-drift equilibrium in subpopulations?
microsatellite data (high mutation rate)
- Fst are based on a priori guesses about population delineation
What does it mean if you find a low Fst value between two subpopulations?
High gene flow
What is implied if you find a high Fst value between two populations?
low gene flow, high genetic differentiation
What are assignment tests used for?
to assign individuals to their most likely population of origin based on genotype
- populations defined a priori, but can help determine dispersal
In an assignment test, what can we assume if individuals are assigned to the populations we found them in?
no dispersal, correct identification of populations
In an assignment test, what can we assume if individuals are assigned to populations other than the one we found them in?
dispersal between two subpopulations
In an assignment test, what can we assume if individuals are assigned to a population that we did not define?
dispersed from a population we did not define a priori
In an assignment test, what can we assume if all individuals are assigned to one subpopulation?
- high gene flow or panmixia
- other populations might not meaningfully exist
When does dispersal not equal gene flow?
when migrants do not reproduce!
- ex. marbled murrelet - high dispersal, but migrants bred less than locals, so gene flow stayed low
How can we infer dispersal from parentage/relatedness?
If offspring are in different populations than their parents!
- ex. pyrenean desman
Why are populations hard to define a priori? (3 reasons)
- home range and long-distance dispersal distances are unknown
- dispersal could be based on something other than adult movement (ex. currents)
- cryptic population structuring (barriers that are hard to observe, ex. reproductive behaviour)
