Week 7 Flashcards
Explain why individual level selection is likely to be more impactful than group level selection.
All it takes is one selfish individual to out-compete the group level selection
Describe the process to define and recognize adaptations.
You can recognize adaptations by:
(1) complexity and design
(2) through experiments
(3) Using comparative methods
Describe the “adaptationist fallacy” and provide other reasons for the existence of phenotypic traits
The adaptation fallacy is based on the assumption that everything is an adaptation or that everything serves a higher purpose.
Sometimes, traits are the spandrel, or “spill over”. Meaning they don’t have any particular reason, more they are a by-product of the true adaptation. You build an arch, you get a spandrel. You build a jaw, you get a chin.
Explain the role of fitness in identifying adaptations
Describe how differential fitness of genotypes (at individual loci) will affect genotype frequencies in subsequent generations.
In directional selection, we see a shift towards the allele that produces a phenotype with greater fitness. This means that the homozygote of this allele is most strongly selected for, but the heterozygote is more strongly selected for than the homozygote of the other (less fit) allele. This is described as a homozygote advantage. In the offspring, we see a gradual increase in individuals towards the favoured allele.
In stabilizing selection, the heterozygote is selected for, described as a heterozygote advantage. The distribution, therefore, will increase at the mean. The offspring will be dominated by heterozygotes.
As for disruptive or diversifying selection, the heterozygote is at a disadvantage. But, unlike directional selection, there is not a gradual degree of selection. So, the favoured homozygote will be greater than the individuals with the allele selected against (which will likely be similar in abundance to each other).
Explain the difference between absolute and relative fitness, and why the latter is more relevant for explaining evolution.
Absolute fitness– per capita growth rate of a genotype (i.e. fitness values of genotypes before standardization)
Relative fitness–fitness of a genotype relative to (a proportion of) the fitness of the reference genotype
Note, by convention, the genotype with the highest absolute fitness is defined as the reference genotype.
Relative fitness is more relevant for explaining evolution because it describes the change in frequency of a trait in relation to other traits (from the same loci) within the population. This is more important for understand the forces of selection and which traits are favoured.
How do you calculate relative fitness and the coefficient of selection?
** Review this worksheet material
(1) Absolute fitness (lambda) is the growth rate, so found by dividing offspring or survived by the original population
(2) Relative fitness (w) is lambda/lambda max
(3) Coefficient of selection (s) is 1 minus the relative fitness
What is an adaptation?
(1) Characteristic that enhances the survival or reproductive success of organisms that bear it relative to other ancestral stages
(2) A process of genetic change in a population whereby, as a result of natural selection, the average state of the character is altered (the population becomes better adapted to their environment)
Define exaptation.
The evolution of a function of a gene, tissue, or structure other than the one it was originally adapted for. Can also refer to the adaptive use of a previously nonadaptive trait (preadaptation).
Describe the different modes of selection (directional, stabilizing, and disruptive).
Directional selection– selection for a value of a character that is higher or lower than its current mean value
Stabilizing selection– selection that maintains the mean of a character at or near a constant intermediate value in a population
Disruptive selection– selection in favour of two or more model phenotypes and against those intermediate between them (aka diversifying selection)
What makes natural selection unique from genetic drift, inbreeding, and gene flow?
Unlike genetic drift, inbreeding, and gene flow, natural selection can act on individual loci independently
What is the coefficient of selection (s)?
Proportion by which the average fitness of individuals of a genotype differs from that of a reference genotype.
In directional selection, the number of generations required for an advantageous allele to go to fixation depends on what three factors?
(1) initial allele frequencies
(2) Selection coefficient
(3) Degree of dominance
