TASK 3 Flashcards
Selection
Natural selection
- individuals that have certain inherited traits tend to survive & reproduce at higher rates –> spread traits that are responsible for it (adaptions)
- population level
- amplify/diminish only traits that differ in individuals of that population
- context dependent
= Heritability + variation + competition (selection)
Reproductive success
- passing genes to the next generation –> they can pass on those genes
- number of offspring produced by an individual + probable reproductive success of those offspring
- mate choice: important factor in this success
Fitness of alleles
- weighted average of the relative productive success of the different phenotypes
- either a genotype or a phenotype
Adaptive evolutionary change
- Evolutionary changes that are adaptive to the given environment
- Such changes increase survival and / or reproduction and are produced by natural selection
Purifying selection
- selective removal of alleles that are deleterious
- can result in stabilizing selection through the purging of deleterious variations that arise
Stabilizing selection
- population mean stabilizes on a particular non-extreme trait value
Directional selection
- an extreme phenotype is favoured over other phenotypes –> allele frequency shifts over time in the direction of that phenotype
Disruptive selection
= diversifying selection
- describes changes in population genetics in which extreme values for a trait are favoured over intermediate values
- variance of the trait increases –> the population is divided into two distinct groups
Mutation-selection balance
- Equilibrium in the number of deleterious alleles in a population
- mutation introduces genetic variation into population while selection reduces it
- level of genetic diversity depends on the relative strength of the two
- -> the more heritable a gene + the more selective pressure the faster selection & evolution
Mechanisms of Maintenance
- -> persistence of variation = why selection may not always eliminate variation
- Heterozygote advantage
- Negative frequency-dependent selection
- Force of mutation
- Inconsistent selection
- Sexuallity antagonistic selection
Heterozygote advantage
- heterozygous genotype has a higher relative fitness than either the homozygous dominant or homozygous recessive genotype
- often due to overdominance (single locus)
Negative frequency-dependent selection
Frequency-dependent selection = fitness of a phenotype depends on how common it is in the population
- negative: fitness of a phenotype decreases as it becomes more common (fitness high when rare)
- -> The trait is only advantageous as long as it is the minority
- Surprise as advantage (left-handers in interactive sports)
Inconsistent selection
- environment changes fast over a short period of time –> selection that begun must be reversed
- selective optimum moves around from time to time/ place to place (e.g. year of draught)
Sexuallity antagonistic selection
- optimal phenotype for a male is not the same optimum for a female
- -> some alleles that improve fitness of males harm that of females & vice versa
Adaptationist stance
- If some feature or behaviour is commonly found in an organism –> probably an efficient design solution to some problem that that organism has faced
- If it were not, then the alleles building that feature would have been out-competed by alternatives that built a different feature
Phenotypic gambit
= forming adaptationist hypothesis directly about the phenotype
- -> without needing to know what the genetic or developmental mechanisms that produce the phenotype are
- validity of this can not be taken for granted
Ultimate explanation
- WHY that particular design increased ancestral fitness
- evolutionary reason
- ultimate explanation of a characteristic that increased compared to others
Proximate explanation
- HOW: which genetical or developmental mechanisms led to the formation of that characteristic in individual organisms
- underlying mechanisms (e.g. different genes, proteins etc.)
Time lags
Period of time between one event and another
Phenotypic plasticity
- ability of one genotype to produce more than one phenotype when exposed to different environments
- -> alter phenotype depending on context (e.g. changing colour)
Shape of the adaptive landscape
- visualize the relationship between genotypes and reproductive success
Sexual selection
- natural selection on the ability to gain mates
- -> individuals with certain inherited characteristics are more likely than others
Sexual dimorphism
- the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs
Intrasexual selection
- selection on the ability to compete with rivals from the same sex
- intersexual competition = competition between 2 individuals of the same sex
Intersexual selection
- selection on the ability to attract members of the opposite sex
= mate choice
Bateman’s principle
- males gain more reproductive success from each additional mating partner than females do
(guys produce unlimited gametes while girls are very limited)
Ornamental Attractiveness
- Sexy son hypothesis
- Good genes hypothesis
Sexy son hypothesis
- mate choice based on one whose genes will produce male offspring with the best chance of reproductive success
(females choose because sons get long tails that makes them more attractive)
Good genes hypothesis
- mate choice based on the male’s ability to pass on genes that will increase the survival or reproductive success of her offspring
(female chooses quality-male because quality is heritable –> better general quality (survive better))
Extra-pair mating
FEMALES
- female mates with males other than the social partner –> extra mate is a “good gene” mate vs. actual partner is of lesser quality but needed to raise the offspring
Sex-ratio
- Ratio of males to females in a population
- In most sexually reproducing species: ratio tends to be 50:50
- -> Fisher’s principle
Hitch-hiking traits / genetic hitchhiking
Allele changes frequency not because it itself is under natural selection, but because it is near another gene that is undergoing a selective sweep and that is on the same DNA chain.
Trade-off traits
- when two traits have opposite effects on fitness but are genetically correlated with each other
- -> costs vs. benefits (e.g. tail length vs. food catching)
- women are choosy: higher cost and lesser benefits for females (have to carry child)
Sex-role reversal
- When males do all the post-fertilisation care
- cost asymmetry between the sexes is reversed (i.e. the males are choosier; Females will be larger/ more ornamented etc.)
Local resource competition
Relatives compete with one another since the local resources are limited
Local resource enhancement
Relatives help one another instead of competing with one another in LRC
Absolute fitness
How many genes contribute to the gene pool of the next generation
Relative fitness
The contribution an individual makes to the gene pool of the next generation, relative to the other contributions of other individuals
Force of mutation
- Genetic variation will persist if force of mutation is strengthened or that of selection weakened
- Polygenic characteristics: effective strength of mutation is proportional to number of genes involved
- Each gene has independent chance of mutating
Genetic drift
= chance events cause allele frequencies to fluctuate unpredictably (at random) from one generation to the next
- can lead to loss of genetic variation –> influences how effectively population can adapt to change
- fixation of alleles
- -> Founder effect: few individuals become isolated from larger population –> establish a new gene pool different from source population
- -> Bottleneck effect: sudden change in environment drastically reduces size of population; certain alleles may be over-/underrepresented/ absent
Neutral variation
= differences in DNA sequence that don’t give an organism a selective advantage/ disadvantage
Testing hypotheses
- Reverse engineering & optimality models (= forward engineering)
- Experimental manipulation & experiments of nature –> comparisons btw. individuals with more or less of a characteristic
- Comparative evidence –> testing across different species that have experienced the selection pressure to different extents (e.g. egg shells)
- Nomological network of evidence (figure)
Optimality modelling
- evaluate the costs and benefits of different organismal features, traits, and characteristics, including behaviour, in the natural world
- allows researchers to make predictions about an organism’s optimal behaviour
Nomological network of evidence
- representation of the concepts (constructs) of interest in a study
+ their observable manifestations, interrelationships among/between
Short-term mating
MALES
- unlike women, men can produce offspring with no cost beyond copulation itself
