lesson 1: local adaptation 1

Question 1

summary of key points in lecture

Answer 1

1. local adaptation definition and future research questions
2. phenotypic plasticity definition + equation (quantitative genetic equation)
3. graph interpretation of local adaptation and adaptive plasticity
4. local adaptation: pattern & process
5. examples of pattern and process mismatch and misinterpretation
6. the reaction norm of local adaptation and phenotypic plasticity
7. anolis lizard example of local adaptation vs phenotypic plasticitt
8. drivers and impeding factors for local adaptations
9. what are requirements for local adaptation, population genetic models (migration and selection rates)
10. local adaptation, local co-adaptation and coevolution
11. detecting local adaptation with reciprocal transplant experiment, what are the controls
12. interpretations of ftness habitat plot and debates

Question 2

what is local adaptation

Answer 2

Local adaptation occurs when populations evolve traits providing a fitness advantage in their unique local environments, leading to resident genotypes having higher fitness than non-resident genotypes in their local conditions. ON AVERAGE

This fitness advantage arises because the resident population has been subject to selective pressures that favor traits specifically suited to their local conditions.

These terms: local environement, resident - what exactly define them? allow for ambiguity in these terms and definition of processes

Question 3

How does local adaptation arise?

Answer 3

Local adaptation arises due to spatial variation in natural selection, causing genetic divergence.
the resident population has been subject to selective pressures that favor traits specifically suited to their local conditions.

there are other processes which lead to local adaptation fitness or outcomes, but the process is not local adaptation, so important to do experiments to identify local adaptations

Question 4

what causes phenotypic variation

Answer 4

1. variations in phenotype can be due to fixed alleles (adaptation or hitch-hike) or due to phenotypic plasticity
2. always important to look at how important evolutionary or adaptive processes are on contributing to phenotyp;ic variation
3. adaptive evolution
4. or random processes such as genetic drift
5. or genetic effects like hitch-hiking genes can all contribute to the appearance/outcome of phenotypic variation –> need to identify whether the outcome is due to adaptation and not other processes

Question 5

what is reciprocal transplant experiment, whar outcomes are expected?

Answer 5

A method where individuals from two populations are swapped and tested for fitness in each other’s environment to assess local adaptation.
Higher average fitness of local genotypes in their native environment compared to foreign genotypes.

Question 6

How is LA both a pattern and a process?

Answer 6

• Pattern: Observable spatial variation in adaptation (fitness differences across populations). is due to a process of LA. QUESTIONS TO ASK: how much variation is being maintained by local adaptation, whats the scale, how does this interact w migration dispersal?
• Process: Evolutionary mechanism by which populations become better adapted to their local environment. QUESTIONS TO ASK: how consistentl,y and how long its taking

Question 7

what is an example where the pattern and process of local adaptations do not match, where one population (non res) has higher fitness than resident even when put in the non-local environment?

Answer 7

1. population A = non res
2. population B = res
3. transplant environment: when you put population A in environment B, the non-res A still outcompetes fitness of res B
4. this could be due to B has a very small population, and fitness is poor in B due to significant effects of imbreeding depression
5. hence even if popA is not LA to environment B, it still outcompetes population B\
6. LA process occurs, but when we test the experiment it doesnt show LA pattern as we would expect
7. difference between pattern and process

Question 8

what is another example of when process and pattern of LA doesnt match? when the pattern doesnt exhibit LA but process does

Answer 8

1. population A and B evolve in response to their own Local environment
2. but selective forces on oth populations are roughly the same
3. so when using the transplant experiment: no difference in fitness even if swapped environments, fitness of both are the same
4. population 1 and 2 are the same: pattern shows no advantage/higher fitness of local compared to non local phenotypes
5. but has LA processs and no LA pattern

Question 9

what is a big problem when doing experiments on LA

Answer 9

1. the use of assumptions
2. when doing reciprocal transplant experiments often substitutes assumption of ‘time’ with ‘space’. hence can often focus on LA pattern but not LA process.

Question 10

what is phenotypic plasticity (PP)

Answer 10

when different phenotypes are produced by a single genotype

Question 11

what is adaptive plasticity

Answer 11

1. when being phenotypically flexible produces higher fitness than being not flexible
2. phenotypically plastic = not genetic based, but due to environmental response

Question 12

when would we see plasticity being adaptive?

Answer 12

1. we would expect to see a plastic genotype being more fit/better than non-plastic ones across a range of conditions
2. they perform better when the environment is variable

Question 13

when would we expect to see the evolution. of phenotypic plasticity?

Answer 13

1. the environment is is variable in time at a shorter scale than generation time (basically if the environment changes more quickly than generation time, you would want the offspring to be phenotypically plastic to adapt to the changing environment and survive more fit)
2. the environment varies in space at a smaller scale than average dispersal distance (similar idea to above, ut essentially dispersal distances would have high variance in environmental conditions)

Question 14

what is a challeng is local adaptation research?

Answer 14

1. difficult to identify whether phenotypic differences are due to phenotypic plasticity or local adaptation

Question 15

what is the reaction norm

Answer 15

1. graphs plotted which describes the pattern of phenotypic expression/plasticity across a range of environment
2. if not plastic, (like limbs on vertebrates) this wont change no matter how much the environment changes
3. often it is a combination of local adaptayion and phenotypic plasticity

Question 16

what happens to the reaction norms graph when there is local adaptation or genotype-by-environment interaction?

Answer 16

1. cross overs
2. where each genotype has the highest fitness in a specific environment or when phenotypic plasticity happens (different reactions to different environments)

Question 17

what is the quantitative genetic formula for phenotypic variation?

Answer 17

1. Vp = phenotypic variation
2. simplest way to look at this is Vp = Vg + Vr
3. Vg is the component of phenotype which is explained by effect of genetics, and Vr is the residual effect of phenotype which cant be explaine by genetics
4. hence heritability is Vg/Vp
5. however phenotypic plasticity is also influenced by environment, therefore the full equation should be:
6. Vp = Vg + (Ve + Vg * e) + Vr
7. Ve is the ffect of environemnt of phenotype
8. Ve + Vg * e is the component of variation due to phenotypic plasticity

Question 18

what does the plot look like when plotting the local adaptation and phenotypiuc plasticity plot on the reciprocal transplantation plot?

Answer 18

1. the two can give very similar plots/patterns
2. but the processes are very different

Question 19

what is the difference betwene local adaptation and phenotypic plasticity?

Answer 19

1. for LA, genotype A native to Hab 1, genotype B native to Hab 2;
2. in PP we typically test the response of genotype A & B across environments that both are found in

Question 20

what is the anolis lizard example and what does it demonstrate?

Answer 20

1. brown anolis loizards are found in the carribean and have undergone adaptive radiation
2. their habitats show a lot of range from trunk to bushes
3. they did an experiment where they first measured the characteristics of these lizards in their original habitats (like hindlimb length) and the perch sizes (wood)
4. they then sampled lizards from one island (staniel cray) and distributed these lizards across 12 smaller islands with less vegetation for 15 years
5. CONDUCTED PCA PLOT: over generatiosn they found that these anolis lizards ‘adapted’ or show correlation between how much vegetation there is and the size of their hing limb lenbgth
6. the longer the perch the larger the hind limb (correlated)
7. they thought this could be explained as there are a lot of hurricanes in that area, on islands with smaller, thinner perches, lizards evolved smaller legs enable to cling on better.

losos et al 1994, 1997

Question 21

what was the plot twist in the anolis lizards example?

Answer 21

1. after a few years they revisited this experiment and realised that phenotypic plasticity and adaptive plasticity could have shown the same effect
2. so they put lizards in cages with different perch lengths
3. and realized after a few months they had developed different hindlimb length through plasticity
4. NEXT RESEARCH/missin research = should have continued to analyze whether the differences between islands are transmitted and passed on to next generations
5. example shows how phenotypic plasticity can occur between generations as well as within population s of same generation
6. complicated differentiating between local adaptation and phenotypic plasticity

losos et al 2000

Question 22

when can we expect to see local adaptation?

Answer 22

depends on balance between:
1. howe effectively natural selection can translate into evolutionary response/pattern
2. other ecological/environmental process which impede selection -> pattern like: migration/random genetic drift, temporal variation in selection, relative differences in selection within. a population, phenotypic plasticity, genetic architecture

Question 23

what are some processes which impede selection -> adaptation

Answer 23

1. migration/random genetic drift,
2. temporal variation in selection: strength of selection varies in time
3. relative differences in selection between neighbouring population (gene flow from no selection population going into strong selection population can. be dilutive)
4. phenotypic plasticity -> harder for local adpatation to occur
5. genetic architecture

Question 24

how might migration and gene flow impede or allow local adaptation to evolve?

Answer 24

1. through 2 simple population genetic models
2. continent island model by haldane wright
3. Two patch model of Maynard Smith and Bulmer

Question 25

what is the continent- island model and what is its significance for migration, selection and local adaptation?

Answer 25

1. continent island model, is where for a single locus there are 2 allels
2. continent A has large population, island b has small population
3. continent A has migration at rate A for allele A, and island b has selection pressure of rate B for allele B (migration from b to a is ignored cuz b has small population)
4. we can determine whether allele B in island B is fixed by looking at 2 properties
5. Sb = the selection pressure for allele B on island B
6. Ma = the migration rate for allele A on continent A
7. and when Sb > Ma, we can see local adaptation of allele B on island B and fixation of this allele
8. PROBLEM: if the variation of migration. and selection pressures varies in time/temporal then this might cause the allele to not beable to fix

Question 26

what is the two patch model and how/when does this cause impede/evolution of LA?

Answer 26

1. 2 populations of 2 island with similar sizes
2. island A has selection pressure A (Sa) for allele A, and migration rate from island A to island B at (Ma)
3. island B has selection pressure B (Sb) for allele B and migration rate from island B to island A at (Mb)
4. Local adaptation occurs when (mb/sa + ma/sb) < 1

Question 27

how can we use the 2 simple population models (2 patch model and continent-island model) to model more complex dynamics?

Answer 27

1. can add in more variables such as: different population sizes,
2. drift in populations
3. partial dominance
4. non-random drift

Question 28

more in depth explanation for factors which can cause local adaptation

Answer 28

1. When gene flow is weak relative to selection
2. When selection is strong & divergent between populations
3. When gene flow is non-random with respect to the environment
4. When there is little temporal variability in selection
5. When there are high costs of phenotypic plasticity (phenotypic plasticity reduces genetic fixation)
6. When genetic architecture facilitates response to selection: Strong linkage disequilbrium (hitch hiking genes)
   Alleles of large effect (or chromosomal inversions)

Question 29

how does coevolution lead to local adaptation?

Answer 29

1. obviously an organism can evolve to adapt to its environment
2. but what if the environment also changes
3. for example in plant herbivore coevolution
4. and host parasite co-evolution
5. both the environment and the target is evolving
6. can evolve in adaptation by one party, or local co-adaptation

Question 30

how can we predict local adaptation in coevolution?

Answer 30

1. predict from generation times
2. if generation time of host is a lot longer generation time than parasite, expect to see local adaptation of parasite to host
3. similarly is plant has a longer generation time than the herbivore, we see herbivore having local adaptation. to trees
4. when host and parasite generation times are more similar, we see local co-adaptation -> this also requires ALL the conditions for local adaptation

Question 31

how to detect local adaptation?

Answer 31

1. Classical method = Reciprocal Transplant Experiment
2. 2 or more populations, take individual.samples from each habitat and swap them to their non-native habitat
3. look at the fitness of samples in native vs non native habitats
4. NEED to conytrol for ‘movement effects’= essentially the process of moving habitats (transporting) can cause different reactions and fitness consequences, so the native samples also need to fo through the same ‘movement’ for control purposes
5. replications to give more than one comparison
6. done in replicable habitats such as sea vs freshwater, contaminated vs non contaminated soils

Question 32

how do we interpret the population habitat interaction plots (plots for reciprocal transplant)

Answer 32

1. normally if they cross over, and sample A is higher than sample B fitness in their natives it means local adaptation, a and b are defo LA
2. however, also debate of graph c, if sample A has higher fitness in its own native environment vs non native, but sample A still has lower fitness in native compared to sample B
3. d is defo not LA, it just means habitat 2 shows lower fitness for both,

kawecki & ebert 2004

Question 33

challenges in local adaptation detection

Answer 33

• Controlling for effects of movement.
• Ensuring replication across multiple populations or habitats.
• Distinguishing LA from phenotypic plasticity.

Question 34

Why is understanding LA important?

Answer 34

1. understand how they are maintained
2. understand what the evolutionary history of a population and factors which drive it
3. identify factors which werent considered before, like anolis lizard example