Adaptive Evolution Flashcards
over what scale can selection act and be detected
Selection can act within a generation and is detected/quantified according to the observed relation between phenotypes (traits) and fitness.
what are the three forms of natural selection
Directional selection leads the mean of the trait towards a specific direction.
Disruptive selection leads a trait away from the mean in both directions
Stabilizing selection leads a trait towards the mean on both sides.
what is directional selection like
Selection favouring a phenotype associated with a particular allele, can result in the allele increasing in frequency in the next generation.
Can lead to an allele being fixed.
what is S
S is called the selection differential and is simply measured as the difference between the average value in the population before selection and after selection.
When can natural selection result in adaptation
If phenotypic differences reflect genetic variation, then natural selection can result in changes in genotype and allele frequencies in the next generation.
How does the HWE and selection interact
HWE proposes the expect result before selection but selection will often cause the results to differ, resulting in different Allele frequencies and genotype frequencies.
What is sexual selection
One component of natural selection is sexual selection
- when differences among individuals in relative fitness arise due to differences in mating success
Sexual selection = whenever a phenotypic attribute of individuals affects offspring production
what does sexual selection explain
This explains the evolution of sex differences in traits that are not beneficial for survival (another component of natural selection)
what is intrasexula selection
Intrasexual selection
- rescue / mate defense
- ex deer antler fencing
what is intersexual selection
Intersexual selection
- mate choice
- ex birds of paradise
what are the four steps animals go through before mating
- Search
- Guard/compete
- Court
- Copulate
What is Sperm competition
Sperm competition: In promiscuous species sperm from multiple males compete in female reproductive tract
what os Cryptic choice
Cryptic choice: Females of some species can bias paternity and use sperm preferentially after copulation. Have spermatheca which store sperm for use. Allows choice.
Some can eject sperm and stop transfer
Which is the choosier sex, why
In most animal systems, females are the choosier sex since they have to facilitate the development of the embryo. Bigger resource cost.
what is Anisogamy
Anisogamy - asymmetric investment into gametes
Predisposition to sex difference in investment in other characters.
what is fitness typically for males vs females in regards to mating
Males: fitness is typically a simple function of number of mates
Females: Diminishing return of mating frequency
what are some cases when males are the choosier sex
Sometimes the typical roles are reversed and male are the choosier sex
In Katydids a female is offered a nuptial gift which is provided by the male in exchange for mating
Male black tree crickets produce a fluid to feed females.
give an example of sexual selection in hermaphrodites
Sexual selection operates in hermaphrodites too
Marine flatworms are sexually reproducing and posses both male and female functions but often engage in penis fencing where the loser gets to be the female and carry the offspring
what is assortative mating
when genotypes or phenotypes bias mating towards (positive) or against (negative) mates of similiar types
Positive = like attracts
Negative = opposite attracts
what is the breeder’s equation
R=h^2S
what is R
the predicted evolutionary response
how can you predict the mean of a trait for the next generation
The mean before selection + R = predicted mean for next generation
how does imperfect heritability affect selection
Imperfect heritability essentially ‘discounts’ selection
R can be 0 if genetic variability is absent or selection is absent.
