Week 10 Flashcards
Determine how to quantify strengths of artificial and natural (linear and non-linear) selection
- The Breeders’ Equation (R=h^2*s)
Using the value s, we can quantify the strength of selection
How do correlations among traits influence our expected responses to selection?
We standardize the phenotypes for comparison and test the strength of selection of different traits and the correlation between selection of these different traits
This is because selection of traits in correlation with one another can produce unexpected responses.
This is because selection can favour certain combinations of traits over others.
How does selection fluctuate across time?
Selection fluctuates over time when the conditions in which the trait that selection is acting upon fluctuates.
So, variation in abiotic conditions (such as temperature, predators)
Ex) fluctuating selection on the growth rate of juvenile ground squirrels; variation in food available to red squirrels (seeds from white spruce, masting species, 5-10 years abundant cone production and then between low or no cone production)
How is the strength of selection used to predict responses to selection using the Breeders’ Equation?
The strength of selection is synonymous with the value of s.
If s is large, selection is strong, and we can expect a large shift in R (the response to selection), represented as a shift in the peak of the distribution.
In other words, the stronger selection is, the stronger the response to selection will be (given that the trait is heritable).
What are some examples of non-linear selection and fluctuating selection on continuously varying traits?
Correlated selection–
Selection favours certain combinations of traits over others
Ex) spotted vs striped colouration and escape behaviour (tendency to reverse course when fleeing) in garter snakes
Fluctuating selection on the growth rate of juvenile ground squirrels (in relation to the seeding cycles of food source trees)
How do you estimate a response to selection using the Breeders’ Equation?
How do you calculate heritability of a continuously varying trait, when given estimates of the variance components comprising phenotypic variance?
(1) Calculate VP (total phenotypic variance) from the sum of VG (genetic variance) and VE (environmental variance)
(2) Divide VG by VP to determine an estimate of the proportion of phenotypic variance with a genetic basis
or
If you have VA (additive genetic variance) or VD (dominance genetic variance) as well as VG, you can calculate narrow-scale heritability (h^2=VA/VP)
How do you use estimates of total genetic variance to estimate broad-scale heritability?
Broad-scale heritability–an estimate of the proportion of phenotypic variance with a genetic basis
BUT does not give an accurate reflection of the amount that will be transmitted between generations
H^2=VG/VP
VG=VA + VD
Where VA is additive genetic variance and VD is dominance genetic variance
Explain how you can use estimates of additive genetic variance to estimate narrow-scale heritability.
Narrow-scale heritability– an estimate of the proportion of phenotypic variance with an additive genetic basis
DOES give an accurate reflection of the amount that will be transmitted between generations
h^2=VA/VP
Explain the process to calculate an expected response to selection, using the Breeders’ Equation.
Determining how heritable a trait under selection is gives insight into the expected response. Knowing how much outside factors, such as abiotic environmental factors, will influence the outcome tells us how uncertain the prediction is as well.
In a parent-offspring regression, heritability (h^2) is the slope.
Maternal effects, common environments, cross foster
The animal model
- This slide I am not confident in, not a lot of information/unclear info
How can we use evolutionary principles to understand phenotypic responses to trophy hunting?
Evolution in response to trophy hunting in big-horned sheep
Horn size determined by: age, genotype, and environment
Favoured by sexual selection
Trophy hunting = selection against large horns
Horn size decline in Alberta in the past 30 years
We can use evolutionary principles to estimate the degree that the genotype influences horn size, and therefore if the decrease is caused majorly by trophy hunting.
What is non-linear selection analogous to?
Heterozygote advantage
What are the components of phenotypic variation?
VP=VG+VE
VP = total phenotypic variance
VG = genetic variance
VE = environmental variance
