Selection and Fitness Flashcards
Type of selection often involving a balance between conflicting selective pressures (often due to trade offs)
Stabilizing selection
This governs reproductive output, has consequences for competitive ability, and also determines what kinds of responses will be deployed to deal with competition
Genotype
Differential reproduction as a result fo heritable variation
Selection
How does selection relate to heritability?
The larger genetic variation is relative to total variation (Vg+Ve), the more effective selection will be. More heritable (closer to 1) = more effective selection
Selection when 2 or more discontinuous phenotypes are fittest (on the ends)
Disruptive selection (diversifying selection)
The fitness of other genotypes that aren’t best are set to this
1-s
What is the value of s always between?
0 (no selection) and 1 (complete mortality)
Reduction in fitness relative to best genotype
Selection coefficient (s)
Effect is modulated depending on population size or density
Density dependent factors
Reproduction at same rate but survive at different rates
Differential survival
These integrate resource availability and competition with population growth
Density dependent factors
Three sets of variables shaping population structure
- # of individual having offspring and # of reproductive offspring
- # of reproducers x # of eggs (upper limit on reproductive output cycle)
- Number of cycles per year and number of female cycles per female lifespan
Selection when individuals at one extreme of the range of phenotypes are the fittest
Directional selection (purifying selection)
Examples of density dependent factors
Supply of food or other resources and Disease
What does changing the 6 factors contributing to fitness change?
Population growth profile
How is death related to reproductive output?
How many died vs how many are produced
6 factors contributing to fitness
- # reproductive females
- # offspring per cycle
- # cycles per unit time
- # cycles per female lifetime
- Death rate of reproductive individuals
- Survival rate of offspring
What causes reproductive output (R) to not be the same for all bearers of a specific genotype?
Environmental effects
Effect is the same regardless of population size or density
Density independent factor
Strength of selection depends on these two things
Heritability (h2) and the degree of difference in fitness among phenotypes
What does fittest mean in survival of the fittest?
The best among known genotype or phenotypes
Examples of density independent factors
Environmental phenomena (drought, long winter, natural disasters, etc)
The sum of viability, mating success, fecundity, gametic viability, and fertilization success
Fitness
Non-random processes through which pre-existing variation is sorted
Differential survival and differential reproduction
Alleles impact the probability that fertilization will take place
Fertilization success
Relative measure of survival and reproduction (W)
Relative fitness
Selection when intermediate phenotype is fittest (middle)
Stabilizing selection (normalizing selection)
Selective regime does not depend on the frequency of the allele in the population
Frequency dependent selection
How is menopause explained by evolution?
Grandmother hypothesis - reproduction gets very stressful at an old age, start to help raise childrens children, idea is to outcompete species who keep reproducing and die as a result
What happens to fitness bc it is relative (and particular to certain conditions)
It changes
Component of fitness stating the probability that individuals learning genotype will survive
Viability
Example of frequency dependent selection
Fish protect against the most common attack side, so mouths on the other side are favored. More mouths appear on the other side in next gen and then the other side is favored. Bounce back and forth
What is reproductive output (R) of an individual?
Probability of fertilization, how many eggs are produced, and survival rate
What are the two requirements for selection
- Phenotypes have heritable basis
2. Phenotypes have varying consequences for fitness
What determines population fitness?
The average reproductive output of the entire population (all genotypes)
Alleles impact the longevity or quality of the egg or sperm
Gamete viability
Reproduction at different rates but survive at same rate
Differential reproduction
The over or under representation of a genotype in the next generation
Fitness
When selection acts to favor a phenotype or genotype
Positive
What is reproductive output of a genotype?
The individual effort of all organisms bearing that genotype
Component of fitness stating number and quality of mates (lots of gametes does not equal high fitness)
Mating success
Selective regime and its impact differ deepening on the frequency of phenotypes or genotypes
Frequency dependent selection
These two influence pop size by limiting the natural, genetically determined potential for population increase
Density independent factors and density dependent factors
What does W + s = 1 indicate?
Relative fitness + selection coefficient = 1
Three species that undergo menopause
Narwhal, Beluga Whale, and Humans
Finches example of selection
Drought years show inc in beak size for next generation and it returns to normal later
Differential survival and reproduction of particular heritable phenotypes
Natural selection
We cant easily determine this bc we can’t tell whether a genotype or phenotype is optimal
Absolute fitness (which individual is most fit)
A heritable trait that increases an individual’s fitness in a particular environment relative to individuals lacking that trait
Adaptation
Component of fitness stating the number of gametes per individual
Fecundity
This type of selection may explain persistence of diseases
Stabilizing selection (sickle cell, dominant = death to malaria, recessive = death to sickle cell, heater = death to neither)
How do fitness differences violate HW equilibrium?
Create differences in successful allele transmission, more offspring will contribute more alleles to the next gen, allele frequencies will not be constant
The fitness of the best genotype is set to this
1
What is fitness determined by?
The reproductive output for each genotype
What does a selection coefficient of 0 represent?
Equivalent to HW assumption of no selection
When will all same genotyped individuals have the same reproductive output?
If the environment isn’t a factor
When selection acts to eliminate a phenotype or genotype
Negative
The nonrandom differential survival and reproduction of particular phenotypes
Selection
The ability of an individual to produce surviving, fertile, offspring relative to that ability in other individuals in the population
Biological fitness
What is reproductive output a balancing act with?
Tradeoffs in cots and benefits. Lots of offspring = lots of energy and less care. Little offspring = lots of care but could still die
