Population genetics - Migration

Question 1

What does migration usual conjur up

Answer 1

Organism moving across space

examples:
1. Wildbeasts across area – variation in raine = drives popultion shifting range

2. Artic turns

Question 2

What do we mean by migration

Answer 2

Emigration + imigration drynamics between sub popultions
- When indiviual in one popultions contrubutes to genes in other popultion

Movement of alleles from one breeding popultion to another breeding popultion
- Indiviouals departing from or arriving in a new breeding popultion

Question 3

What does migration violate in H-W

Answer 3

H-W = no one can go in or out –> when you are born into a popultion you contrubute to that popultion and no one comes in
- Violating the 3rd assumption

This is the assumption we are violateing to model migration

NOW the gentic makeup of the new generation is NOT just a function of within popultion reproductive dynamics – NOW it also includes some input from other popultions

Question 4

Migration example

Answer 4

Can get movemnt between the forest and evergaldes black bears or night not get any migration

Individuals going between popultions birng alleles to the other popultion –> move from one gene pool to another gene pool

Question 5

Two models of migration

Answer 5

1. Continent island model – larger popultion going to smaller
2. Two island model – recpiprcal gene flow (this is the one we use)

Question 6

Migration model

Answer 6

Start = have 2 subdivided popultions with difefrent alelles frequnceies

AT H-W –
Poplation 1 – P = 0.8 –> p1 = 0.8

Popultion 2 – P = 0.2 –> p2 = 0.2

At H-W the allele frequencies would stay the same (no migration) –> BUT THEN we can swap individulas at a rate of m

m = proportion of one population that will contrubute to reproduction pool of other popultion in the next generation

Question 7

m in migration models

Answer 7

Proportion of popultion that contributes to the next generation of the other popultion

HERE = we assume that m is the same for both popultions
- We could do m1 and m2 for each popultion BUT we willl treat m symetrically

Question 8

Things we need to account for in migration model

Answer 8

1. m – proportion of popultion that contributes to the next generation of the other popultion
   
   • Input
2. m - 1 – need to account for individuals leaving popultion (need to take account loss)
   
   • Loss from original population
   • Loss of migrants from our focal popultions

Question 9

Change in allele frequencey in migration model

Answer 9

Get chnage in allele frequency because move individuals in and out = undergo evolutionary change

Looking m and 1-m = allele frequencies change

Question 10

Mathamatical model of migration

Answer 10

𝑝′1 = (1 − 𝑚) (𝑝1) + (𝑚)(𝑝2)
- 1-m X p1 – only have individulas with p1 allele frequncey
- m = migration rate
- m X p2 – get indiviuals at a raye of m at P2 allele frequncey

𝑝′2 = (1 − 𝑚) (𝑝2) + (𝑚)(𝑝1)

p’ = allele frequncey in the next generation

Question 11

Answer 11

(1- 0.05) X (0.8) – only 95% f 0.8 allele frequncey contribute to next generation

(0.05) X o.2 - 5% of popultion have frequncey of 0.2

Because the system is symetrical migration chnage alelle in both popultion by same amount in different direction (because same m)
- Since we set up the system to be symetrcal (same m for both) = they change by the same amount

Question 12

Change in alelle frequncey in both popultions

Answer 12

Because the system is symetrical migration chnage alelle in both popultion by same amount in different direction (because same m)
- Since we set up the system to be symetrcal (same m for both) = they change by the same amount

Question 13

Answer 13

Popultion A – allele frequnceies are close together
- P goes up in ine popultin and down in the other by the same amount
- Allele frequncey chnage in A is smaller than B because allele frequncey in A is already similar to begin with

Popultion B the allele frequcneies are far apart
- Even though the allele frequncey is NOT the same = the allele frequcney chnage is still is –> means that suymetery in chnage is not because of p being mirrories it is becuase m is the same

Pop A vs. Pop B.
- Allele frequncey chnage in A is smaller than B because allele frequncey in A is already similar to begin with

Question 14

Affect of same m

Answer 14

If m is the same = p chnages by the same amount in different directions in both popultions
- Even though the allele frequncey is NOT the same = the allele frequcney chnage is still is –> means that suymetery in chnage is not because of p being mirrories it is becuase m is the same

dP = same –> sign is different but the absolute value is the same
- Even if allele frequncey is not symetric dP still is if m is the same for both popultions

Question 15

What is happening with migration over time

Answer 15

Use general dP –

dP = m(p2 - p1)
- Assume m is the same
- p2 - p1 – Frequcney of same allele in popultions 2 vs population 1 –> drives magnitude of change

Question 16

End point of migration

Answer 16

if dP = 0 –> get equillirbium point - get an end point of popultion

IF migration is ongoing dP = 0 when P2 = p1 (when the allele frequnceies are identical)
- Have end point in middle + know what endpoint is

END – P2 = P1 –> end is when dP = 0

Question 17

Migration is…

Answer 17

Determanistic – have an endpoint and know what the endpoint os –> if you know the start you can know what effect will be
- Migration will go until p2 = p1

Question 18

Effect of migration

Answer 18

Migration acts to decrease genetic diffeerntaion between popultions – homogenizes genetic varaition across subdivided popultions
- If migration keeps occuring popultions will evenually have the same alelle frequncey
- Makes allele requncies of popultion more similar through time until there is no difference between thwm

Homogenize until get equal Pt (will end equal to the frequncey across popultions Pt)

Question 19

Pt

Answer 19

If two popultions were in one popultions what would overall p be
- Allelic varaition in total popultion if subdivided were in one popultion
- Pt = used to find Ht = Heterpzygosity across popultions

THIS is what migration pushes P to in each popultion – pushes to average of 2 alleles
- Migration acts to drive P1 and P2 towards PT

Question 20

FST of drift vs. migration

Answer 20

Drift = increases FST towards 1
- Drift = makes Pt less similar
- Increases differences between popultions

Migration decreases FST towards 0
- decrwases difefrences between popultions
- Make popultions converge of Pt

Migration and drift = in direct opposition
- If migration acts to dirve P1 and P2 towards PT = acting in direct opposition of drift

Can find an equillirbium between the two

Question 21

Meaning of FST

Answer 21

Increase difefrence between popultions

FST = 1 = no shared alleles (have P = 1 and P =0)

FST = 0 – ni allele frequency differences (they are the same)

Question 22

FST

Answer 22

The measure of genetic differentiation between subdivided popultions

Question 23

Drift vs. Migration

Answer 23

If migration acts to drive P1 and P2 towards Pt = acting in direct opposition to drift
- Effects can be viewed in terms of FST

Have an equillibrum point where forces balance out

Question 24

Drift vs. migration equillbirum point

Answer 24

FST>

Question 25

Size of m and FST>

Answer 25

If m is smalle (less than 10-15%)-- can calculate FST at equillirbium between drift and migrayion --> 𝐹𝑆𝑇= 1/4𝑁𝑒𝑚+1 Nem = efefctive popultion size times the migraytion rate = the numver of effective migrants per generation - Nem = improtant term - Assume that level of FST = due to equillibrum between drift and migration = can use FST to see number of migrants moving in generation ***Ne and m = hard ot gte iun popultionn but they are meaningful

Question 26

Use of FST

Answer 26

Assume that level of FST = due to equillibrum between drift and migration = can use FST to see number of migrants moving in generation Given a value of FST = can find Nem = can find expected number of effective migrants - Here we assuime that the popultions are at equillbirum

Question 27

Answer 27

FST = 0.0476 --> FSt is much closer to 0 than 1 = these popultions are much more alike than they are different

Question 28

Changing Ne

Answer 28

If increase Ne -- loosing FST vakue = FST decreases Increase Ne = FST decreases because ability for drift to maintain allele frequncey difefrences decreases and migration is strong Increase Nem = favor of migration over drift = become similar Decrease Nem = favor drift = miantain differences

Question 29

FST> with larger popultion size

Answer 29

FST> = 0.0243 Increase Nem = favor of migration over drift = become similar Decrease Nem = favor drift = miantain differences

Question 30

FST at equillibrium

Answer 30

if m is small we can calculate FST at equillirium between drift and migration FST> = 1/4Nem+1

Question 31

Nem term

Answer 31

Effective population size times the migration rate -- it is the number of effective migrants per generation

Question 32

Meaning of FST

Answer 32

FST = equilibrium point between the effects of drift and effect of migration - It is a function of migration rate and strength of drift THIS IS A PUSHING EAQUILLIBRIUM = stable equillirbium between the two forces

Question 33

Affect of drift vs. Affect of mutation

Answer 33

Drift = causes allele frequncey to be more different Migration = Homogenoizes to Pt (Causes allele frequncey to be the same) We can define an equillrbium point

Question 34

FST

Answer 34

Metric of genetic difference between populations -- how different are two populations genetically - Look at FST by looking at varaition within and across popultions -- take observed vs. expected form

Question 35

How do we find FST (overall)

Answer 35

Take observed vs. expected form - Compare heterozygosity in sub popultion to total variation FST = Ht - Hs/Ht - Ht = like epxected -- expected H if they were one popultions - Hs = observed H (Avg of sub H) Observed parameter vs. expecteation given null Pt (all varaition -- if were one popultion) vs. how varaition is distrubuted in subdivided popultions (Hs)

Question 36

Observed in FST Vs. Expected in FST

Answer 36

Observed = looking at varaition within popultions (Hs -- avergae varaition within sub popultions) Expected = null --> Null that 2 population stae part of one popultions - All alleles in both popultions that mized as if they were one popultions THEN what would H be (THIS IS Ht) - Null = treating as one popultion -- Avg H if one popultion

Question 37

FST (1 or 0)

Answer 37

FST = 1 -- P = 1 and P = 0 --> H = 0 - Hs = 0.5 --> between the two of them - All of varaition is between the popultions NOT within FST = 0 -- all varaition is within subdivided - P = 0.5 and P =0.5 -- allele frequencey is the same in both popultions Low FST -- allele frequncey in popultions are close together

Question 38

Ht

Answer 38

Heterozygosity across both popultions - Equal to or greater than variation within subdivided popultions Uses Pt -- Average between P of both populations

Question 39

What can we use FST for

Answer 39

Given a value of FST -- we can find the expected number of effective migrants (Can find Nem) - Can get the number of individulas moving between 2 popultions - Can use FST as equillirbium point --> calculte equillirbium level (FST) given strength of drift and migration rate BUT if we assume that something is already in equillirbium amd we measure FST (we know about strength of drift and migration) --> use FST to find Nem ***Can assume that the popultion we are exmaining is in equillirbium

Question 40

Answer 40

Looking at how connected the 2 popultions are IF FST = 0.5 -- assume equillirbium Nem = 1/FST/4FST Nem = 1-0.5/4X0.5 = 0.25 - Nem = effective number of migrants 0.25 --> means have 0.25 individuaks (can be decimal because its an average) - Means -- 1 indiviuals every 4 generations (the popultions ate quite isolated) - 0.25 is NOT the migration rate -- it is the avergae number of migrations per generation

Question 41

Answer 41

Looking at how indepent the popultions are --> you can find genotype frequncey --> use that to find FST --> get Nem FST = 0.203 --> pretty intermediate Nem = 0.981 --> If allelic varaition is driven by long term drift + migration = get 0.981 deer each generation - 0.981 deer going from one to other (Since symetric = goes both ways)

Question 42

Pairwise effects of forces

Answer 42

1. Mutation selection balance - Mutation adding alleles and NS getting rid of them - s and u 2. The dual effect of drift and mutation driving neutral molecular evolution - Drift regarless of popultion size drives genotypic variation between two species - u and N 3. The tension between drift and migration in subdivided populations - m and N

Question 43

Mutation selection balance/Mutation and drift

Answer 43

Had fairly straight foward outcomes - Mutation creates varaition and drift Stable equillibrium Example: Mutation creates varaition and drift turns some of it into substitutions at a constant rate - Straight foward outcome in nucleotide substitution --: drift taking mutation and carrying it to fixation - u drives nucleotide substitution rate because Ne is in both equations = cancels out = only u affects the rate of process

Question 44

What drives nucleotide substitution rate

Answer 44

u drives nucleotide substitution rate because Ne is in both equations = cancels out = only u affects the rate of process

Question 45

Nature of drift and selection

Answer 45

Selection = determanistic --> predictable Drift = Stochastic --> don't know direction Differences in nature of them = makes intercation complicated ***They are two of the strongest forces -- how do they interact - Complicated Since drift = always happening --> means that selection is always at play with drift

Question 46

Drift and selection interaction

Answer 46

IMAGE: - Left of 0 = selection predominates (negitive selection) - Line at 0 = drift predominates - Right of 0 = positive selection -- selection predominantes - INtersection of lines -- point where drift = acting soley on alleles -- there is no difefrence between drift affect on alleles and NS affect Deviation from balance between Drift and mutation (deviation from intersection) = based on 2Nes Probability of mutation being lost due to drift = more likley (1-1/2N) Image = shows drift + selection simultaneously in a system (violating infinate popultion size) Overall -- there are osme parameters where selection will predominate and spme where drift will - Popultion size decreases = stringer strength of ____ for selection to be predominante dirver of allele frequncey chnage - Selection needs to act alongside drift -- relative strength pf 2 ffoces = affects if selection can occur Take home message -- the relative magnitude of selection and drift matter -- they often behave as if one force is predominant over the other

Question 47

Probability of allele going to fication

Answer 47

Probability of new allele going to fixation = 1/2N --> relative increase or decrease of probabiliy of going to fixation = based on 2N

Question 48

What effects if selection can occur?

Answer 48

Selection needs to act alongside drift -- relative strength pf 2 forces = affects if selection can occur

Question 49

Importane of drift vs. selection

Answer 49

There are ranges of parameter space where one is much more important than the other

Question 50

Drift + selection on adaptive topographies

Answer 50

NS = acts to push popultions uphill -- increase average popultion fitness (will go to make w/) - Will keep going until get to a local maxiumum value of w/ How will drift affect AT? ***Drifts tendencey is not to go downhill it is just to move in either direction BUT at fitness peaks there is no where to go but down so drift pushes popultions off of fitness optima Drift = changes alelle frequnceies randomly back and forth - When at w/ (When at stable equillibrium) you can only go down in w/ BUT drift is not trying to decrease w/ it is just causing p to move randomly on X axis - Drift causes back and forth movement from one generation to the next BUT if at w/ then drift can only move w/ down = drift decreases w/ because only way to go BUT if popultion is not at w/ (not at equillirbioum) then drift is equally likley to go in both dorections (Can make it decrease w/ OR can make it go uphill to w/ fatser) - If no where to go but down drift can push popultion off of w/

Question 51

Strength of NS + drift on AT

Answer 51

Steepness of slope = proportional to the strength of selection - If steep -- a small chnage in P = bigger change in fitness = stronger repsonse of NS = NS can counteract affect of druft more readily (when steep drift is constrained on how much it can chnage things because NS can put it back to w/) - Steep -- NS is going to give strong pushback as drift is moving the popultion around - If shallow (less steep) = can move p a lot without a big change in W/ --> when p chnages and effects w/ THEN drift can drive the system more stringly (because NS isn't ask strong if less chnage in w/) --> drift has stronger effect here - If shallow -- the NS pushback is much weaker = drift has a much freer hand Smaller popultion size = affect but drift is large = harder for NS to keep popultion at an optimium

Question 52

NS + Drift acting on beneficial recessive alleles

Answer 52

Recall -- NS acting on beneficial recessive alleles has a hard time getting started (Slow at the start) NS + drift = particularly impirtant for beneficial recessive alleles Begging of recessive alelle increasing (starts slow) --> drift can move things very readily + selection is weak -- drift is strong - At low frequnceies when it is very shallow -- drift can be strong --> the most likley outcome is that the benefical mutation will drift to zero before NS can get any traction - Beneficial recssive allele = more likley to be lost due to drift than they ate to go to fixation - Porbability of going to fixation is 1/2N BUT probability of not fixing = 1-1/2N --> drift is main threat to benefical recessive - Recessive benefical is likley to be lost due to drift before selection can bring it to fixation (more likley lost than selection taking hold and incerasing it) Phenomon = Holding seive

Question 53

Halanes seive

Answer 53

Overall: At low frequnceies when it is very shallow -- drift can be strong --> the most likley outcome is that the benefical mutation will drift to zero before NS can get any traction - If beneficial mutations act in rescive fashion = most liklet will come and go to drift long before selection has a chance to act on them - Sometimes these mutations can reach high enough frequncies to start being visable to selection through drift Effect of drift on recssive benefical alleles at low frequencey --> most is lost due to drift before selection can take hold and do things (bring to fixation) - Affects rate of selection

Question 54

Affect of drift on rate of selection

Answer 54

Already have low mutation rates --> mutations rates give us mutations but drift can make is lost -- can lose it befgore selections can do things = even lower rates of increase benefical recssive mutations

Question 55

Drift increase or decreasing beneficial mutation

Answer 55

Drift can inrease are decrease BUT it is more likley to lose it (to decrease) because once it hits zero its gone - If you have limit that affects increase/decrease for good + if have one copy --> if you lose one copy = its gone --> loss is more likley than increasing to go to fixation Creates limitations of NS acting on new alleles

Question 56

Outcome for new reccessive benefical allele

Answer 56

Evolutionary outcome for new recessive benefical alleles is heavily influnces by drift

Question 57

Migration + Natural Selection

Answer 57

The influx of alleles from other populations can also push populations off and adaptive peaks, or prevent them from getting to them in the first place - Migration coming in adapted to different environments = can push population off of peak

Question 58

Migration load

Answer 58

A lower average population fitness than predicted given selection regime due to migrants from populations with different selection regimes - Knowck off optimum because influc of alleles adapoted elsewhere - Espcially bad at edge of range

Question 59

Where does migration load have big effect

Answer 59

Often effects at the edge of species ranges - When populations are well-adapted (high mean fitness) in the center of their ranges, they may send out a lot of migrants --> These migrants can interfere with local adaptation at the range edge- perhaps even determining the range limit itself

Question 60

Example of migration load

Answer 60

Butterfly -- sub optimally adapted to conditions --:> reason is because butterfly coming to island - Get warm adpated end in small popultion = can't adaopt to local climate

Question 61

Can migration be good?

Answer 61

Migration is not always bad --> add variation IF the strength of selection = proportional to varaition - Selection = lose varaition - Waiting to get varaition through mutation (mutation is a slow source of new varaition) --> get little variation -- low rate of mutation = doesn't give varaition + lose a lot of mutation = ability to adapt if run out of varaition -- wait a while to get varaition through mutation BUT migration can add varaition - Migration = can get new alleles into focal popultion that NS can act on --> might not need to worry about losing alleles because can have others with those alles come in - Migration can be very effective force for infusing popultions with new varaition on which selection can act

Question 62

Migration affect on NS

Answer 62

Migration - can help or hinder adaptation due to NS

Question 63

Is pushing of adopative peaks always a bad thing?

Answer 63

If have scenerio in image --> You can go to w/ = 0.35 OR can go to w/= 1 IF p goes to p> = it will stay there -- this is bad because low w/ -- NS can't move it from the valley BUT other evolutionary forces can - If went to the right of valley = would go to p = 1 -- would end at w/ = 0.35 - If have other forces with selection = won't get stuck there --> drift can chnage { and can drift acros equillirbium to the left and NS can then bring it to P = 1 - Selection can't do this by itself but it can with other forces -- drift opens up posibility - Selection + drift = two step process involoving chnage in predominance of first (first drift predominates then selection) OR migration can come in -- other population with benefical allele can come in -- they can send migrants --> migrants can go to the focal popultion and can bring P across equillibrium and allow NS to bring P = 0 and w/ = 1 NS by itself can't bring the popultion to the global optimum but selection in conjuction with other forces can

Question 64

Wrights theory (overall)

Answer 64

Back during the modern synthesis, Sewall Wright proposed a model for how the interplay of evolutionary forces might be a more powerful mode of evolutionary change than selection by itself - Thinkning about limits of NS and need other dorces to get complex traits It’s called ”shifting balance” between it involves shifts in the predominance of the evolutionary forces acting on a species - Think about how relative importance of forces might shift in system

Question 65

When is wrights model useful

Answer 65

Particuly useful for thinkning about ways that evolution can act when adaptation is complex - Model on how to adapt across rigged AT --> how to cross adaptive valley if NS can't do that by itself

Question 66

Rugged adaptive topographies

Answer 66

Have more than one local maximum

Question 67

How to think about Rugged topographies

Answer 67

It is more realistic to think in multiple dimensions Example -- image - Can see two traits - Rugged topography because 2 points of high fitness states --> Can't go between points without decrease w/ --> NS can't go between them itself - Have local optimum at combination of low values or trait 2 and moderate values of trait 1 - Have global optimum at combination of moderatley high values of trait 2 and highest values of trait q - Highest fitness = high trait 2 and high trait 1 - There are two possibilities on high w/ based on right combination of trait values --> need right combo to have right value

Question 68

Going from local optimum to global optimum with on NS

Question 69

What makes adaptive topographies rigged

Answer 69

Epistsis -- due to epistasis --> intercation between loci and affect on fitness - Cam't know affect of 1 locus on fitness without knowing the state of other trait - Affect of Trait one depends on state of trait 2

Question 70

Epistasis + NS

Answer 70

Epistasis = majore hindernace on effects of NS Need other forces of have epistasis Epistatic rigged topography -- multiple genes affect trait --> get both to move in right direction together -- hard for NS to do

Question 71

Example -- 2 locus fitness epistasis

Answer 71

Has two fitness peaks + 2 low vallues A1 has high fitness in presence of B1 - A1 = only high fitness with B1 A2 only has high fitness in the presence of B2 - High A2 and B2 = high fitness Wrong combo of alleles = decrease fitness If to the left of valley = fix for A1B1 BUT if to the firght of balue fix for A2B2 Have Adaptive topography for A with w/ and Adaptive topography with B for W/ --> put them together to see interaction

Question 72

What does wrights model work best for

Answer 72

Wright’s model occurs takes place on rugged adaptive topographies, but also works best in subdivided population -- works best in subdivided popultions Works best in subdivided because small popultion = increase drift + subdivided can have migration + mutation popultion drift independtley

Question 73

Wrights model (overall)

Answer 73

Idea of how evolution could work NOT saying that it is universal + logical expliantion of evolving forces = allow popultions to evolove - It is a hypothsis on how it can happen Model = 4 Stage model – 4 ”shifts of balance” among evolutionary forces and one shift from within population dynamics to among population dynamics Wright’s Shifting Balance Theory

Question 74

Wrights model (Slides)

Answer 74

Step 1 – in individual subpopulations – drift can predominate if population sizes are small (relative to “height” of fitness peak) - If this is happening in multiple subpopulations, some of these populations are likely to end up the bases of better optima Step 2 – When drift brings the population in contact with a steep fitness slope, the strength of selection starts to outweigh the effect of drift – selection pushes the population up the peak - As mean population fitness increases, population size is likely also increasing Step 3 involves a shift toward dynamics among populations – large high fitness populations are likely to produce a lot of migrants - These migrants can influence the evolution of other subpopulations - This influx of new variation pushes the 2nd population of its local peak – specifically in the direction of the peak in population 1 Step 4 occurs when this push from migration allows selection to take over in the 2nd population – driving it towards the global optimum Overall: The interaction of evolutionary forces acting across large subdivided populations might allow for complex adaptation that natural selection can’t drive by itself

Question 75

Wrights model (Mine)

Answer 75

Step1 -- all subdivided popultions = stuck on bad fitness peak --> NS can't act to get to a better position (because at a peak) -Height of peak is proprotional to W/ -- depends on reproductive sucess - Low w/ = popultions staying small + low fitness = popultion decreases = cam drift heavily --> drift has string hand and NS will be weak --> can have random change in alelle frequncey - Random chnage in allele frequncey due to drift = csan be going on in 10 subdivided popultions independentley -- all random change due to drift --> eventually popultions will leave peak - Drift will predominate unless the frequncey goes to a slope and NS can accelerate THEN -- as popultion increases = drift acts less --> Selection will increase w/ to go up peak and get to a new peak = optimum fitness When increase w/ = now hvae high probability of S/R = increase popultion size = can be highest w in subdivided popultion = NOW need to send migrants to other popultions - Healthy popultion = only sending migrants out (not symetric) Migrants now influence P in other popultion -- other popultions in other peak can have low drift out-- if send migrants from original popultions chnage P in other popultion determansticallty towards higher peak (not random) --> NS can bvring to peak after migration -- NS can take over and end at overall species wide adaptation in complex trait END = species wide adpatation in complex trait SHOWS -- NS can drive complex adptation in com face of epistasis --> other droces play important role NOT just NS -- need other mechansims to get adapative being

Question 76

Height of peak on Adaptive topographies

Answer 76

Height of peak is proprotional to W/ -- depends on reproductive sucess - Low w/ = popultions staying small + low fitness = popultion decreases = cam drift heavily

Question 77

What does Wrights model explain

Answer 77

Explains how complex adaptation can occur Using other forces = we can epxlain how complex adaptation can occur --> NS can't do it by itself -- relies on importance of forces shifting across process

Question 78

What creates rugged adaptive topographies

Answer 78

Epistatic interactions in multiple loci under selection created rugged adaptive topographies --> requires changes in multiple sets of genes at ince

Question 79

Limitation of NS

Answer 79

NS can't explor broader adaptive space itself (in rugged adaptive topographies) because only goes uphill -- it can get stuck at a sub optimal peak Using other forces = we can epxlain how complex adaptation can occur --> NS can't do it by itself -- relies on importance of forces shifting across process

Question 80

One shift within wright model

Answer 80

Shift from within sub populations to between sub population ***Works when in sub popultions Step 3 = Shift within sub popultion to between sub popultion

Question 81

Wright (2)

Answer 81

Start = popultion stuck in sub optimal peak -- NS is stuck (w/ can't go up anymore) --> at a low w/ at start Beceasue at low w/ = low reroduction output = small popultion = drift -- HERE drift can predominate and selection is weak Stage 1 = drift = random chnage in allele frequncey -- each sub popultion is independent of each other --> in some of the sub popultions = the popultion will move to go towards a better fitness peak due to drift --> when it reaches a steep slope = NS increases in strength (Strength of selection = proportional to slope = NS is stronger) --> NOW selection takes over - Selection is strong --> Selection will take popultions up to optimual fitness peak = w/ increases - Selection increases -- drift decreases AS w/ inreases = Popultion size increases - At new peak w/ increases = get more offspring = popultion grows NOW -- go from within popultion to ACROSS sub popultions If 2 sub popultions increases popultion size = it will disproportionaly send migrants to other popultions --> NOW other popultions is driven by migrants BY sending out migrants = affect allele frequncey of other popultion = affect evolution of other popultion - MIgration = determanistic = more efficient - Sending migrants from one popultion to other = change allele frequcney in other = pull other popultion towards higher w/ on Adaptive topography -- NOT random like drift -- going to specific to higher peak Other popultion goes to optimal peal - Selection = takes over in other popultion (takes over within popultion -- NOW back to within popultion) to drive up to optimal peak - Now within popultion again - Selection takes over again

Question 82

Applying wrights shifting balance -- What does Wrights hypothesis mean?

Answer 82

Example -- Malaria We know Anemia C alelle = almost completley resistant to malaria but it is in low frequncey Because it is in low frequncey NS = can't act on it - Constaint on NS --> doesn't mean contraint on evolution entirley -- can change using other forces To have C allele increase in the past they could have had = not in large popultion in Afirca but in small sub popultions where drift infleunces BUT they are also connected enough that mogration can carry alleles - In the past they could have had small communities with drift but have migration - As the popultions grow = drift decreases + limit subdivision = less likey for drift/wright and NS will happen THIS in crease in C didn't happen because of our interaction with malaria is recent --> we didn't interact with malaria until agriculture - Human malaria = because of trade and traffic with madacagscar -- change in standing water = malaria infects humans now - Here there is no longer condition for drift/migration to drive adapatation