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49 Cards in this Set

  • Front
  • Back
Bateman's Principle
Eggs are expensive to make, sperm is cheap. Females are limited by resources; males are limited by their access to females. Consequently competition tends to be between males.
Sexual selection
Differential reproductive success due to variation among individuals. Theory: If there is heritable variation in a trait that affects the ability to obtain mates, then variants conducive to success will become more common over time. (According to Bateman, sexual selection will be a more potent force in the evolution of males than the evolution of females.)
Intersexual selection
Selection to attract a mate. Bright colors, dancing, big tail, etc. Ornamentation. There is a choice made by one sex (usually the females).
Intrasexual selection
The result of competition within a sex for access to mates. Fighting. Phenotypes generally include weaponry.
Why are females choosy?
1- Just because/sensory bias.
2- Direct benefits to offspring/female that increase fitness.
3- Fisher's Runaway Process.
Fisher's Runaway Process
Explains why females arbitrarily choose certain male traits.
1- Some males have a trait that allows them to survive better.
2- Most females in the population develop at least minimal "choosiness" for that trait.
3- B/c females prefer males with that trait (blue) they mate with more blue males and produce more blue males as well as more females who prefer blue males.
4- Becomes positive feedback loop.
5- At some point blue males are getting more mates, but also dieing more often.
6- Eventually blue males are so disfavored by natural selection that their net advantage goes away.
Direct Benefits
Reason for female choosiness that increases her (or the offspring's) fitness. Male traits in case of "direct benefits" tend to be benficial to females--not just ornamental.
3 Ques of Quantitative Genetics
1- How much variation assoc. with a trait is genetic?
2- To what extent can we predict offspring phenotype from their parents?
3- Can we predict how some trait will evolve (given some kind of selection acting on it)?
Assumption of genetic variation curve
All alleles are additive (heterozygote is exactly 1/2 way between the homozygotes or two alleles--one that increase phenotype and one that decreases phenotype.)
To get overall genetic value add together affects of all alleles. This works within a locus or across loci.
Relationship between phenotypic, genetic, and environmental variance
Vp = Vg + Ve
Predicting offspring phenotype with two parents who are each 5'2" and there is not environmental variation acting.
Ave genetic value of parents = 5'2"
Ave genetic value of offspring = 5'2"
Do parents that are extreme (v. tall or v. short) produce offspring that are equally extreme?
NO--as long as there is environmental variation.
Narrow sense of heritability
1- The extent to which we can predict offspring phenotype from parents' genotype (h squared)
h squared = 0.325 means that 32.5% of the difference from the mean gets passed on to the offspring.
2- Represented by the slope of the regression line relating the average of parental phenotypes to the average of their offsprings' phenotypes. If the slope of the line = 1, then there is no environmental variation in the population. With more environmental variation the slope gets shallower and our ability to predict what offspring look like decreases. (Environmental variation decreases h squared.)
3- h squared equals the fraction of difference between parents and the overall mean that is passed on.
4- h squared = the proportion of total phenotypic variation that comes from additive alleles.
What causes the majority of phenotypic variation?
Environment (The majority of phenotypic variation is environmental in origin.)
Define S & R
S = (the selection differential) the difference between the ave. phenotypes of breeding individuals and the overall ave. of the population

R (the response to selection) = the difference between the next generation and the current generation (on ave).
Overtime the response to selection may reach a plateau that means
narrow sense heritability (h squared) must decrease over time as S (selection differential) stays constant.
**Selection decreases variation (in particular additive variation--variation propels selection but is used up in the process, like gas in a tank).
Genetic drift
Increases genetic variation between populations while decreasing variation within populations. Drift happens more rapidly in smaller populations.
Mutation rate from A to a
mu (backwards y)
Mutation rate from a to A
nu (bubbly v)
Which is a stronger force: mutation or selection?
Selection tends to be stronger
How to determine variation in a population...
heterozygosity = expected frequency of heterozygotes (measure of variation)
homozygosity = measures lack of variation in a population
Heterozygosity decreases over time while homozygosity increases. Heterozygosity decreases faster in smaller populations.
2 ways to become heterozygote:
1- completely random mating (outcrossing)
2- inbreeding/selfing (finite population)
Phylogenetically Independent Contrasts--When a correlation exists
1- The correlation does not exist b/c of common ancestry; the trait has evolved independently in each species.
2- Hints pretty strongly at natural selection (adaptation). Lots of evidence for directionality (drift doesn't predict directionality). Can't test directly against null hypothesis of drift.
Fixed differences
Fixed differences are between species and represent a new mutation that has spread to fixation.
Differences between individuals of the same species. (Have not gone to fixation.) Polymorphisms are the opposite of fixation--variation.
Basic facts of molecular evolution
1- Fixations (substitutions) due to drift (rate = mu) happen much more slowly than fixations (substitutions) due to selection (rate = 4N(mu)s
2- Mutations that change the protein sequence are more likely to be under selection than those that don't.
(3- If detrimental alleles fix, it's always due to drift, not selection.)
Synonymous Mutations
(silent) Mutations that don't change the protein. Use as control. They show us what's happening with only drift.
Non-synonymous Mutations
(replacement) Mutations that change the protein.
Pattern of non-syn to syn ratio...
non-syn/syn = 0 then non-syn mutations are strongly selected against (no non-syn mutations in pop)
non-syn/syn = intermediate (ex: 0.003) then still selecting against non-syn mutations, but not as strongly.
non-syn/syn = higher (ex. 0.36) then either selection against the non-syn (bad) mutations is weaker OR some protein changes are actually beneficial
When ratio is 1 or above it's GREAT evidence for selection of beneficial alleles that have spread throughout the population.
Naive prediction
If selection for beneficial mutations has been important then the rate of substitution/fixation of protein changing mutations should be greater than the rate of fixation of non-protein changing mutations.
**This is naive because natural selection may be acting against detrimental alleles.
**With fitness reducing mutations we expect the opposite of this naive prediction.
Selective sweep
Positions on chromosome where beneficial mutation goes to fixation and "sweeps" away all polymorphism. Polymorphism = 0.
(Genetic hitchhiking)
McDonald-Kreitman Test
1- If some mutations (in particular the non-syn) are beneficial then the ratio of non-syn to syn will increase as the mutations get older (increase over time)
2- If all mutations are neutral, the non-syn/syn ration stays the same
3- If some non-syn mutations are detrimental, they drop out of population immediately--never get common enough to be detected in the population.
McDonald-Kreitman test is powerful because
It allows us to detect selection and provides control that allows us to distinguish between NS for beneficial changes and relaxed selection against deleterious mutations.
3 requirements for natural selection to act
1- Variation for a trait
2- Inheritance of that variation
3- Variation in survival or reproduction assoc. with variance in the trait
Twelve Evolutionary Trends & Characteristics of Primates
1- Generalized skeleton
2- Free mobility of fingers & toes
3- Replacement of claws with nails
4- Decreased olfaction
5- Increased reliance on vision
6- Reduction in number of teeth
7- Abbreviation of snout
8- Trend toward erect posture
9- Elaboration of brain
10- Increased body size
11- Prolongation of life span
12- Adaptations to single births
Generalized Skeleton
-hasn't changed much in 70mya (very similar to ancestors)
-double bone in limbs
Free Mobility of Fingers & Toes
-opposable thumb
-allow precision grip
-young hold onto mother 24/7 (humans only to break this except some "primitive prosimians"
Replacement of Claws with Nails
-improves ability to feel
-exceptions: grooming claws (prosimians, marmosets & tamarins)
-dermatoglyphics = fingerprints = ability to hold onto things (reflects importance of touch in primates) touch becomes basis of love
Decreased Olfaction
-loss of rhinarium (wet nose) - prosimians still have, monkeys don't
-vomeronasal system (internal & connected to amygdala (limbic system = emotion, fear, etc)- prosimians and NW have, OW, apes, us don't have
-less scent marking
-smell becomes less important as we move up the primate ladder
Increased Reliance on Vision
-stereoscopic vision (eyes in front, field of vision overlap = depth perception)
-color vision
-nocturnal -> diurnal (except owl monkey & tarsier, no tapetum)prosimians have
Owl Monkey & Tarsier - Return to Night
no tapetum, eye shape similar to diurnal species (who see color) therefore we know ancestors of these primates was diurnal and sometime reverted to being nocturnal
Reduction in Number of Teeth
ancestral = 44 3-1-4-3
primitive primate = 40 2-1-4-3
NW monkey = 36 2-1-3-3
OW monkey, ape, human = 32 2-1-2-3
**grinding teeth in back are decreasing- the premolars in particular
exceptions: marmosets/tamarins 2-1-3-2
and aye-aye 1-0-0-3 (coconuts, insects)
Abbreviation of Snout
exception = baboon
-associated with other trends: eyes to front, scent decreased in importance so teeth must decrease b/c no room
-example of neoteny (over course of evo. time begin to look more infant-like; flat face is character of young mammal)
Trend Toward Erect Posture
-vertical clinging & leaping (ex: bushbaby)
-ischial callosities (b/c spend more time sitting, free hands to eat, etc.) **ONLY in OW monkeys, NOT NW monkeys
Anatomical Changes Needed for Bipedalism
-heel/tripod placement of foot- chimps stand on side of foot (spread weight)
-change in angle of femur
-change in pelvis shape (more "bowl-like")
-change in curve of vertebral column (C to S shape)
-move foramen magnum forward to balance head like "lolly-pop"
**stood up first, then we became human (massive change in brain)
Elaboration of Brain
-hemispheric size (cortex, with exception of olfactory cortex which gets smaller)
-visual cortex (back of brain, occipital lobe)
-association and limbic areas
**chimp/ape brain 1/3 the size of ours--they're not just hairy humans)
Increased Body Size
-lower metabolism (BMR = 70W to the 3/4)
-hair density decreases
-sexual dimorphism increases - only contradiction is monogamy
-move into diurnal niche if greater than 1 kg prosimians, the smaller ones are nocturnal
Prolongation of Life Span
Lemurs: 4m pregnancy, 3-6m infancy, 1-2 @ puberty, 15yr lifespan
Monkeys: 6m pregnancy, 6-12m infancy, 3-4 @ puberty, 20-30yr lifespan
Apes: 8m pregnancy, 3-5yr infancy, 8-12 @ puberty, 40yr lifespan
Humans: 9m pregnancy, 5yr infancy, 11-14 @ puberty, 50-80yr lifespan
Adaptations to Single Births
-2 mammary glands
-bicornate uterus to unicornate uterus
-epitheliochorial to hemochorial placenta (more attached/invasive/bloody)
-external maternal care
-carrying infant from birth
-female sociality