lesson 3: local adaptation 3

Question 1

summary of this lecture local adaptation 3

Question 2

what are some assumptions about local adaptations in the sea (marine ecosystems)

Answer 2

1. recall: sa > mb (Haldane-Wright model); (mb/sa + ma/sb) < 1 (Maynard Smith-Bulmer model
2. • Relative homogeneity of marine systems over large scales (little variation in s)
   • Long-distance dispersal & hence gene flow (large m)
3. traditional assumptions: local adaptations would be very difficult to evolve because of the 2 population models
4. the 2 population model suggests that for LA to evolve there should be little migration and big selection.
5. however in marine environment, it is often believed that the environment can be quite homogeneous (not much change across the geographies) (little difference in selection pressure) and that the migration and dispersal distance are very far (lots of gene flow and migration) -> difficult for LA to be maintained

Question 3

what are some more new insights and challenges of traditional marine local adaptation views on the homogeneous environment in marine?

Answer 3

1. environmental variability actually shows a lot of heterogeneity (so selection is not homogeneous and varies): abiotic factors like temperature, littoral/reef environements, solar insolation -> influence biotic factors
   * for Example: Pacific Ocean off California shows sea surface temperatures ranging from 8°C to 24°C over ~100 km -> drive different water chemistry changes. Sharp discontinuities in temperature gradients driven by processes like upwelling (topographically stable features).
   * abiotic factors such as wave action, salinity, chemical concentrations also vary over relatively small spatial scales which influence different selection pressures
   * These environmental differences are often stable over time, supporting persistent selective pressures.

Question 4

what are some new insights and arguments for local adaptations in marine (dispersal/migration distance)

Answer 4

1. genetic tools used to measure dispersal
2. dispersal distance really depends on individual species’ life history strategies
3. huge variation between species: fish dispersal 50-200km; marine snails less than 10km can be as little at 2m
4. still a lot smaller scale than we expected (relative to the entire marine)
5. Even across scales of 10 to 200 km, populations can experience limited gene flow, leading to opportunities for local adaptation.

Question 5

what evidence do we have on local adaptation in marine?

Answer 5

1. review on 59 case studies on marine invertebrates local adaptation
2. 66% shows local adaptation occuring be4tween 100-1000km (which in relative to the size of the marine ecosystem is quite a small dispersal region) -> they measured distances between populations
3. so even for marine species with planktonic larvae which generally have a very. high dispersal distance, its is only 1000km, which is relatively a small dispersal spatial distance; this suggests that selection counteracts the homogenizing effects of dispersal
4. moreover, although the more strict sense of local adaptation is genetic divergence across generations, in marine local adaptation can also b e interpreted as within-generation selection without persistent genetic divergence across generations -> balances polymorphism
5. local adaptation occurs when selection dominates dispersal over large selective gradients (big difference in selection pressures)
6. Differentiation arising from within-generation selection occurs when dispersal is high, but selection repeatedly filters non-adaptive genotypes in each generation -> local adaptation

Sanford & Kelly 2013

Question 6

how does local adaptation arise in marine?

Answer 6

1. Differentiation arising from within-generation selection occurs when dispersal is high, but selection repeatedly filters non-adaptive genotypes in each generation.
2. local adaptation within each generation due to high selection gradient. leading to balanced polymorphism
3. Significant local adaptation is commonly observed even at relatively small scales (< 1000 km), contrary to traditional assumptions of homogeneity in marine systems.
4. Dispersal and Selection:
   Long-distance dispersal does not entirely prevent local adaptation when selective pressures are strong and consistent.
5. Balanced Polymorphism vs. Local Adaptation:
   Differentiation from within-generation selection (balanced polymorphism) is distinct from local adaptation, which requires genetic divergence maintained across generations. some argue balanced polymorphism is a type of local adaptation within a generation, filtering out maladapted phenotypes

Question 7

what is the argument about blanced polymorphism and local adaptation?

Answer 7

1. argue that balanced polymorphism is local adaptation within a generation with great selection pressure gradients.
2. if repeated over generations can be viewed as local adaptation?
3. more viewed as a process of local adaptation

Question 8

What is the traditional assumption in local adaptation studies?

Answer 8

1. Assumption: Local adaptation is driven solely by direct effects of host genes.
2. Host genotypes determine phenotypes, which adapt to specific environments.
3. host genotypes are the main factor for local adaptation process and pattern observations

Question 9

how is our view on local adaptation challenged by microbial interactions with host (microbiomes)

Answer 9

1. microbial mediation can influence host fitness without changing host genotype, by interacting with its environement
2. example: Hosts from one population may perform better in a new environment because they acquire beneficial microbes, not because of genetic changes in the host.
3. microbes can enable adaptive plasticity in different environments without altering its genome
4. this challenges th eidea that heritable genetic changes are always required for adaptation
5. host microbe co-adaptation: co-evolve. microbiome itsefl is under selection, and not just the host. microbiome becomes part of the adaptive system

Question 10

Does Microbial Mediation Avoid Host Genetic Changes?

Answer 10

1. it can complement or enhance host genetic adaptation, doesnt eliminate changes
2. Influence selection pressures on the host genome, potentially shaping long-term genetic changes of both the microbe and the host or as a microbiome
3. shows adaptation is not simply genetics based and is a combo of plasticity (short term) + genetics (long term)

Question 11

What are the two types of microbial effects on local adaptation?

Answer 11

1. microbially-mediated local adaptation (MMLA): Interaction between host genotype and local microbial communities.
   Adaptation occurs because hosts are better matched to their local microbes.
   Example: Plants from a specific population perform better only when paired with their native microbial communities.
2. microbially - mediated adaptive plasticity: Microbes enhance phenotypic plasticity of the host.
   Hosts perform better in specific environments when paired with beneficial microbes, regardless of origin.

Question 12

walk me through how MMLA and MMAP in 2 plants (P1,P2) and 2 microbials (M1, M2) are influenced

Answer 12

1. Environment directly affects the genotypes & communities of both hosts & microbes (MMLA)
2. 2 & 3: Microbes and host reciprocally affect each other
   - e.g. host genotype may determine microbial community; microbial community may influence host phenotype. selection pressures reciprocally - co-evolution and local co-adaptation (MMLA)
3. Local microbe communities may have direct effects on fitness of local hosts, compared to non-local microbial communities on local hosts. (MMAP) without changing the genotype of host -> shows microbes locally adapted to maximise plasticity and fitness of local host.

Question 13

summary of the effects of fitness - habitat plots plant 1,plant 2, M1, M2

Answer 13

1. b graph shows that without local microbes, even when transplanted = no change in fitness, no local adaptation seen
2. c: with local microbes and transplanted we see local adaptation and increase in fitness of local plant in local environment - only observed when paired local microbe w local plant
3. d: with local microbe but not local plant -> higher. fitness but no local adaptation

Question 15

What experimental designs are used to further tease apart and test microbial mediation?

Answer 15

1. Plants from Population 1 (P1) and Population 2 (P2) are grown in both locations.
2. Soil sterilization and microbial inoculation treatments:
   * Autoclaved soil:
   * Removes microbes.
3. Reintroduced microbes from local or foreign populations.
4. Vary three factors:
   * Environment (E).
   * Host genotype (Gp).
   * Microbial community (Gm).

Question 16

What interaction outcomes indicate host microbe coadaptation?

Answer 16

1. when they varied host genotype (Gp) and microbial community (Gm)
2. Soil steriliza,on treatments to test effects of ± microbes
3. graph b shows transplantation of P1 and P2 with the same native microbes and a changing environment/location/soil
4. Plants paired with microbes from their native source show consistently higher fitness, regardless of the transplant environment.
5. P1 plants with P1 microbes have higher fitness in both P1 and P2 environments.
6. suggests a strong host genotype x microbe interaction (Gp x Gm)
7. suggests host microbe co-adaptation

Question 17

What experiment outcomes indicate host MMLA?

Answer 17

• Systematically varying Environment (E), Host Genotype (Gp) & Microbial Community (Gm).
• MMLA: vaired microbial community:
• they varied all 3 E, Gp, and Gm in this case
  1. Microbial Variation: Microbial communities were sourced from P1 and P2.
  2. Host Variation: Plants from P1 and P2 were transplanted to both P1 and P2 environments.
  3. Environmental Variation: Plants and microbes were tested in both P1 and P2 environments to observe how plant fitness depended on the interaction of microbial source, host genotype, and the transplant environment.
  4. all 3 effect the fitness of the plant
  5. and only when all 3 are present -> local adaptation

Question 18

what about MMAP?

Answer 18

This graph highlights that microbial communities (Gm) have environment-specific effects on plant fitness, irrespective of the plant’s genotype.
The interaction between microbial source (Gm) and environment (E) drives fitness differences, showing that microbes mediate adaptive plasticity.
Microbial fitness effects are context-dependent:
P1 microbes enhance plant fitness in P1 environments.
P2 microbes enhance plant fitness in P2 environments.