1&2:Adapation and Speciation Flashcards
Natural Selection
non random process by which biological traits become more or less common in a population. Key mechanism of evolution.
Natural Selection will occur when
individuals are variable in some traits, at least some of this variation is heritable, individuals with some trait values survive or reproduce better than others.
Darwin’s major insight
that heritable variation can, under the right conditions, lead to speciation.
Alfred Russel Wallace
developed the theory of natural selection at the same time as Darwin, joint manuscript with Darwin.
Galapagos Islands
characteristics introduce different selective pressures to organisms in the islands.
Galapagos Finches
differently shaped bulls as result of natural selection
Selection differential
the mean value of a trait after selection minus the mean value of that trait before selection.
response to selection
mean value of a trait in the next generation minus the mean value of that trait before selection.
Fitness
The ability for an organism to pass its genes on to the next generation.
What are the types of selection
directional, stabilizing or purifying, and disruptive
Directional
favors phenotypes at one end of a distribution. The population evolves in that direction.
Mean phenotype: increases or decreases depending on what is selected for
Variance in phenotype: not necessarily changed
Stabilizing
selection favors values towards the middle of the distribution.
Mean of phenotype: does not change
Variance: decreases because the phenotypes at either end of the distribution have been selected against.
Disruptice
favors phenotypes towards the ends of the distribution (farther form the mean)
Mean phenotype: no change as long as individuals on both ends of the distribution have equal fitness
Variance of phenotypes increases.
Frequency dependent selection
occurs when the fitness of a genotype depends on its frequency in the population
Negative frequency dependent selection
a phenotype has the greatest selective advantage if its is rare.
Positive frequency dependent selection
a phenotype has the greatest selective advantage if it is common.
Direct Fitness
contribution that an individual makes to the gene pool through their own offspring
Indirect Fitness
comes from an individuals genes being represented in the gene pool of subsequent generations because their relatives, with whom they share alleles, successfully reared offspring
Direct Fitness Part 2
determined by the number of offspring an organism produces over its entire lifetime.
Life History
timing and the duration of key events during a life time (age, duration of reproduction, number and size of offspring produced) that can influence an organisms fitness
Life History Trade Offs
- Current reproductive success
- Future reproductive success
- Likelihood of surviving
Formula to find offspring each year
Max number of os
Survival vs Reproduction
one strategy: High survival, delayed reproduction.
Guppes of Northern Trinidad
Above Waterfalls: low predation, high sruvivial
Below waterwalls:
high predation, low survivial
Extrinsic Mortality
rate at which eternal events (predation, starvation, infectious disease) leads to death in a population
Intrinsic Mortality
rate at which internal events (aging, disease, mutations), lead to death in a population.
Senescence
decline with age in per capita reproductive performance , physiological function or the probability of survival
Antagonistic Pleiotropy
allele can be favored because it benefits early life survival or reproduction even if it has very determinital effects later in life.
Individual Selection
differential performance of individuals causes some genotypes to replace other genotypes.
Group Selection
differential performance of groups of individuals causes some groups to out compete and replace others. But selection can favor cheater phenotypes within groups, undermining group selection for altruism.
True Altriusm
reduces inclusive fitness. rare, because it is evolutionarily disadvantageous
