Week 11

Question 1

population genetic structure is caused by

Answer 1

Geographic barriers to gene flow/habitat patchiness/low dispersal
Historic events
Natural selection

Question 2

which type of structure is determined by

Answer 2

Interaction of landscape structure and population history evens and natural history of the organism (such as dispersal)
It can be very different for organisms even in the same habitat

Question 3

ephemeral vs stable populations

Answer 3

Ephemeral - metapopulations, population units interconnected by gene flow, extinction/recolonisation
Stable - continuous population structure and isolation by distance

Question 4

genetic markers

Answer 4

Genetic variation is sampled appropriately
Population genetic models linking genetic variation and processes
Statistical tests of which models best fit

Question 5

models should be

Answer 5

Simplify complicated systems so we can see important factors
Allow predictions that can be tested with experiments or observations

Question 6

discrete subpopulations

Answer 6

island, stepping stone

Question 7

isolation by distance

Answer 7

continuous

Question 8

island model

Answer 8

All subdivisions can exchange migrants
Distance does not impede gene flow
Aphids are excellent dispersers

Question 9

stepping stone

Answer 9

Dispersal is more likely between adjacent subpopulations
Distance does impede gene flow
Gallwasps is an example

Question 10

isolation by distance (Wright)

Answer 10

Series of overlapping neighbourhoods
Distance does impede gene flow
Many organisms show this pattern
Virtually any species in continuous habitat with somewhat restricted gene flow/dispersal

Question 11

how can we know which population genetic structure applies?

Answer 11

Different models make different predictions about the relationship between genetic drift and geographic distance
So with genetic data sampled over a range of distances, we can infer what model applies

Question 12

Fst properties and inferences

Answer 12

A common measure of genetic difference between subpopulations
It cannot be negative - any slight negative values are just estimates near 0
Increases with genetic difference in allele composition between subpopulations
Ranges from 0 to 1
If it is 0, there is no meaningful difference between subpopulations
Most similarity comes from commoner alleles rather than very rare ones
Fst will be larger for a pair of subpopulations when they differ more in their expected heterozygosities for the same alleles

Question 13

two attributes of Fst

Answer 13

Amount (effect size)
Statistical significance

Question 14

biological factors that change Fst

Answer 14

neutral: genetic drift/dispersal/habitat structure/time
Small populations diverge faster due to drift
Fst increases as gene flow among demes decreases
Non-neutral: natural selection

Question 15

Fst vs geographical distance

Answer 15

Steeper means stronger spatial population genetic structure for less-good dispersers (less gene flow)
Is steeper in fragmented than unfragmented habitat
Fragmented habitat has less gene flow so Fst increases with distance

Question 16

Fst vs natural selection

Answer 16

Increases with diversifying selection strength (selection works to make demes different). Ne makes a lot of difference when selection is stronger
Reduces under balancing selection - works to make demes similar

Question 17

what are genetic distance models concerned with?

Answer 17

Genetic distance models are fundamentally concerned with connectivity of individuals and genes among populations
More connected populations have a more flat genetic pattern
Connectivity helps with survival

Question 18

metapopulation

Answer 18

Population of populations
United by extinction and recolonisation

Question 19

population connectivity

Answer 19

Demographic connectivity + genetic connectivity
Demographics looks at growth rates affected by immigration, emigration, death and birth rate between populations
Genetic connectivity depends on the absolute number of genetically effective dispersers (Nm)
High levels of dispersal might not lead to demographic connectivity if they are countered by low recruitment and survival
Demographic connectivity is very hard to measure in the field (watching immigration, births, deaths…)
Cannot estimate demographic from genetic tho (not always anyway)

Question 20

gene flow

Answer 20

Matters because it can speed up or slow down evolution
Can alleviate inbreeding
Two types of genetic connectivity are characterised by gene flow and Fst: adaptive connectivity (bring in useful new alleles) and inbreeding connectivity (avoid harmful inbreeding)