2. Local Adaptation: Conceptual Bases Flashcards
Structure of the lecture
- Classical methods
- Modern methods
- Combining both classical and modern methods
What are the examples of classical methods that can be used for LA?
1
- A. thaliana
- Strenotrophomonas
- Horse Chestnut trees
What are the classical methods to measure LA that can be used?
1.1
Reciprocal transplant experiments.
Introduction of organisms from each of the two environments into the other
How was LA tested in A. thaliana?
1.2
Agren and Schemske, 2012
Performed RTE between two locations that were ~2000km apart (Italy and Sweden)
Large spatial and environmental distances
Measured lab-germinated seedlings every year for 5 years
testing site x population
Results: in 8/10 comparisons, LA was shown to be acting. showed that there were actually significant effects of site x population x year, with large variation occurring each year. selection pressure might have been winter survival due to soil temperature
shows the large scale of LA
How was LA tested in Strenotrophomonas bacteria?
1.2
Vos et al., 2009
25x25cm grids on Port meadow
Bacteria and pooled bacteriophage were isolated from each square
Reciprocal Transplant
Found that phages were ~9% more infective to local, rather than foreign bacteria. No correlation between LA and distance, and the scale of LA was on the order of cm. Local phage between at infecting the local environment than non-local
Shows that LA can occur on a small spatial scale
What did the meta-analysis from Hereford et al., 2009 show about LA?
1.3
Compiled studies of LA done in the wild
74 studies (50 plant, 21 animal, 2 fungi, 1 protist)
1367 measures of fitness, yielding 892 measures of LA.
Strength of LA was unrelated to environmental difference between the populations.
Found that LA =
fitness (native) - fitness(non-native) / Mean fitness
What are the two major modern methods that can be used to study LA?
2.1
- Pairwise comparisons (can test at the level of single populations or multiple populations)
- Genome-Wide Association Studies - allows for the identification of associations between traits and genes within populations
How have modern methods to test LA been used in Sticklebacks?
2.2
Testing the EDA locus, which controls the number of bony plates in sticklebacks, depending on the local environment of the stickleback.
Plates are related to predation function
marine and freshwater sticklebacks were crossed to see which gene controls bony plates
sampled sticklebacks of both populations from across the world, based on the phylogeny of the sequence at the EDA locus vs., 30 other genome positions
seen that marine and freshwater cluster separately, meaning that they must share a common ancestor
selection for parallel evolution
LA
How can we use modern methods to understand LA in human populations?
2.3
Can understand how some particular traits can accumulate in different populations due to LA. For instance, the EDARI1 locus is associated with thick hair is highly prevalent in China
What are two combined methods of understanding LA?
3
- Crypsis genetics
- Experimental Ecological Genomics
How can we use Crypsis genetics to model LA?
3.1
Genetic variation that does not contribute to the normal range of phenotypes that are observed in a population. Frequently dealing with simple spatial contrasts. Replication across closely related species.
Seen in Chaetodipus intermedius, in which there is a correlation between rock reflectance and mouse coat reflectance that is shaped by geographic area and on-lava/off-lava substrate (Hoekstra et al., 2005)
How can we use experimental ecological genomics to measure LA?
3.2
Exploration in the field that is then transferred into genomics data.
(Barratt et al., 2019): Nebraskan Deer Mice which either have light/dark sites coats corresponding to the sites they are from. Being same colour as the environment was advantageous. Survival strongly predicted by fur colour. Genotyping of Agouti mice found one SNP with maximal effect that strongly affected brightness, and decreased over time in dark experimental settings.
