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81 Cards in this Set
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- Back
- 3rd side (hint)
Linkage disequilibrium
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Allele at one locus is non-randomly associated with allele at another locus
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Non-random assoc. of alleles at 2 different genes in a population
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Linkage equilibrium
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Allele at one locus is independent of allele at another locus
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Evol at one gene doesn't affect evol at another gene
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D
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coefficient of linkage disequilibrium
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D=0 if
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genes are independently sorting, because...
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all combinations are equally frequent
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When linked genes show LD
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chromosome freqs will change from one generation to the next, moving toward linkage equilibrium
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Factors that create linkage disquilibrim
1. 2. 3. 4. 5. |
1. Selection on multilocus genotypes
2. Physical linkage 3. Genetic drift 4. Population admixture 5. Assortative mating |
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What reduces LD?
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Sexual reproduction. How?
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Meiosis, genetic recomination, outbreeding
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Usefulness of LD?
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1. Detect physical linkage
2. Map genes for trait of interest 3. Infer population history 4. Detect positive selection on genes |
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LD example:
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Ashkenazim with 8-repeat locus more likely to have 84 GG disease mutation
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Able to date disease via the rate of recombination (750-2325 years ago)
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Selective sweep
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(aka hitchhiking) neutral genetic variation linked to a positively selected mutation will also become more prevalent
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That haplotype becomes only one in pop, resulting in large reduction in total genetic variation in that chromosome region.
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Sexual reproduction reduces LD
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via meiosis and genetic recombination
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Sexual reproduction is costly because...
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1. Cost of finding mates (time and energy)
2. Exposure to disease 3. Possible infertility 4. Two-fold cost of males |
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Explain the 2-fold cost of males
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Parthenogenetic females can make 2x as many offspring
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Draw it out.
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Why sexual selection better?
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1. Genetically unique individuals
2. Recombin. create new multilocus genotypes 3. New combinations may be more fit 4. Breakdown LD |
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Muller's ratchet
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Genetic load (deleterious mutations) increases; decreases fitness
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Sexual pop. can purge deleterious mutns. Long term benefit of sex.
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What are the short-term benefits of sexual repro?
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1. Adaptation in a heterogeneous environment
2. Some multilocus g.t.s favorable in one envt; less favorable in future envt. 3. Quick evolution for orgs locked in evol arms race. But... |
Sometimes sexual repro is favored by competitors (e.g. parasites favoring sexual repro in snails)
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How is LD created?
1. 2. 3. |
1. Selection. How?
2. Drift. How? 3. Migration.How? |
1. can't predict freq of haplotype by multiplying freq of alleles
2. Finite population - fixed for A. Mutation causes A->a. Now always linked to b because occurred on same chromosome. 3. Pops start in LE. Mix pops together and observe LD. |
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Compare sexual selection to natural selection
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Nat Sel: selecting more fit indivs (better at repro)
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Sex Sel: selecting indivs better at obtaining mates
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Derived character
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evolved in response to a selective agent.
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"Everything was perfectly designed for its purpose." Viewpoint known as
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Panglossian. Held until 1960s when...
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biologists began recognizing trade-offs.
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Antagonistic pleiotropy
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Gene that regulates more than one trait; some may be bad for fitness.
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What did the Spandrels of San Marcos analogy predict?
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Architectural consequences of the arches coming together were not intentional, just there
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Can't assume every feature is an adaptation.
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How can we test hypotheses about adaptations?
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1. Experimentation
2. Direct observation 3. Comparative method |
1. Involves some kind of manipulation
2. Relies on measurement making w/o interference 3. Spp. are not indepentdent data points |
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Testing an adaptation example: Why do zonosemata flies wave their wings?
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To deter jumping spiders by mimicking major predator.
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Comparative method accounts for...
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phylogeny
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Remove effects of relatedness so evaluation is more compatible with statistical methods.
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Independent contrast
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A comparative method testing mode for adaptation (example- testes size in large bat social group)
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1. Compare sister taxa as pairs
2. Any difference btwn species must have been acquired AFTER divergence from a common ancestor 3. Slide all points (now lines) so one point meets origin of graph 4. Treat remaining points like a regular regression |
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What are limits to adaptation
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trade-offs, constraints.
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What is the Darwinian Demon?
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1. Sexually mature at birth
2. Infinite offspring 3. Reproduces constantly 4. Immortal |
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Why doesn't the Darwinian Demon exist?
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1. Energy-limited
2. Biological processes NOT instantaneous 3. Physiological and evolutionary TRADE-OFFS 4. Ecological context (competition, density-dependence). |
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Sexual dimorphism
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Phenotypic differences
among males and females of the same species in secondary sexual traits. |
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Sexual selection:
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Exaggerated male traits may arise because they
increase male mating success. This advantage should be large enough to compensate for negative effects on survival or fecundity. |
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Difference between natural selection and sexual selection
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Natural
1. Variation in trait among individuals 2. Variation in trait is heritable 3. Some individuals are more successful at SURVIVING to reproduction than others 4. Reproductive success is non-random (individuals with favorable form of trait REPRODUCE more) |
Sexual:
1.Variation in trait among individuals (expression of trait may be restricted to 1 sex) 2. Variation in trait is heritable 3. Some individuals are more successful at OBTAINING MATINGS than others 4. Reproductive success is non-random (individuals with favorable form of trait MATE more) |
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Darwin's quote about sexual vs. natural selection
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“Sexual selection depends on the success of certain individuals over others OF THE SAME SEX, in relation to the propagation of the species; while natural selection depends on the success OF BOTH SEXES, at all ages, in relation to the general conditions of life.”
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What did Trivers 1972 explain?
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Exaggerated traits mostly in males because...
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Differences in parental investment among males and females.
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When does sexual selection occur?
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Member of one sex (usually male) compete with each other for access to mates.
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If sexual selection occurs in males, what can be expected?
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• Males limited by number of females to mate with
• Females limited by quality of mate • Greater sexual dimorphisms • More ornamented or brightly colored males. |
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What are the consequences of sexual selection?
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1. Male-male competition
2. Female mate choice. |
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Examples for each adaptation testing method:
1. Experimental 2. Direct observation 3. Independent contrast |
3. Testes size in bats
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Forms of male-male competition
1. Form I 2. Form II 3. Form III |
1. Combat
2. Sperm competition 3. Infanticide. |
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Which form of male-male competition may lead to alternative mating strategies?
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Form I: Combat.
Example? |
Sneaker males
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What does sperm competition favor in males?
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Mate guarding, large testes, copulatory plug, structures that remove other sperm.
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What are the explanations (hypotheses) of female choice?
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1. Good genes hypoth
2. Direct benefit 3. Sexy sons hypoth 4. Pre-existing sensory bias hypoth. |
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Good genes hypothesis says females asses genetic fitness in males...
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If trait is costly, indicates male quality, developmental
robustness, resistance to parasites |
e.g. long calls in frogs.
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Direct benefit hypothesis
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If males provide resources, females directly assess quality of resources
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May translate into higher repro fitness for both sexes.
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Sexy sons
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Runaway process; preference has no genetic correlation
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Females mate with sexy males because sons will also be sexy. Thus she will have higher repro fitness.
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Pre-existing sensory bias
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male trait exploits pre-existing sensory bias
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e.g. male fiddler crabs build hoods over burrows - look like shelters to females. Males court from within.
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Male choice e.g. in pipefish
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Females larger and have stripes. Males are the choosy ones.
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Types of social interactions
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Cooperative
Selfish Altruistic Spiteful. |
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Kin selection - selection applied to the family.
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Natural selection favoring the spread of alleles that increase indirect fitness.
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indirect fitness
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reproduction by relatives made possible by an individual's actions.
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Kin selection is...
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-Natural selection based on inclusive fitness
-Process by which traits are favored because of their beneficial effects on the fitness of relatives. |
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Kin selection predicts...
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1. that idivs must dispense benefits more often to kin than to non-kin
2. certain behaviors to be more common among relatives: altruism, cooperation 3. selfish and aggressive behaviors to be less common among relatives. |
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What is Hamilton's rule?
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Br - C > 0
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B= benefit to recipient
C = cost to actor r = coefficient of relatedness. |
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Selection favors altruism if...
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it increases indirect fitness
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Cost/benefit are measures in units of surviving offspring.
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Kin selection requires...
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kin recognitiion. Examples?
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Spade footed toad morph.
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In kin selection, the allele for altruism...
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Increases by playing the odds
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The more closely the actor is related to the beneficiary, the more likely the beneficiary also carries the altruism allele.
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Greenbeard effect
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an alternative to kin selection. Does not require discrimination among relatives
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Allele causes carrier to grow a green beard, which is recognizable on others. Behave altruistically toward other green beards, and the greenbeard allele will spread.
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Slime mold aggregates as greenbeard example
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wild-type csA cells are suckers, make up larger portion of stalk in lab (non-reproductive), but...
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In soil, wild-type cells are altruists toward each other, so altruistic allele higher in freq than knock-out cell.
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Eusociality
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-Indivs cooperate in caring for young
-Reproductive division of labor (sterile workers likely) -Generations overlap. |
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Why is eusociality common on hymenoptera?
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Haplodiploidy
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Bros. and sisters only related through their mother.
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Haplodiploidy
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male haploid (develop from unfertilized eggs); females diploid
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So sisters are 3/4 related to e/o, 1/2 to own offspring and 1/4 to brothers.
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Kin selection predicts conflict of interest
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Sisters more related to each other than brothers
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Favors 3:1 sex ratio. Workers destroy male eggs.
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Does haplodiploidy explain eusociality?
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Problems:
-Multiple matings by queen could make workers more related to offspring than to sisters -More than one queen may exist in a colony -many eusocial species aren't haplodiploid (termites, naked mole-rats). |
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Eusociality evolution
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Eusociality evolved in taxa that build nests and take case of young for extended periods
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Paper wasps - workers not sterile
-but more successful when co-found nests. |
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Parent-offspring conflict
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Parent related to offspring equally (r=0.5).
-Conflct btwn parent and offspring -Indiv offspring monopolize parent -Parent wants to maximize fitness of ALL offspring. |
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Types of parent-offspring conflict
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-Weaning conflict
-Harassment -Siblicide in boobies |
-Mom gets more benefit by reproducing again than producing milk for current offspring
-Bee-eaters harass closely related kin (prevent from nesting) to recruit them as helpers to their parents? -First hatchling pushes out unhatched egg; older sib kills younger in food shortage (long term) |
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What is cooperation among unrelated individuals called?
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Reciprocal altruism
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What does reciprocal altruism require?
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1. Repeated interactions among same individuals
2. Many opportunities for altruism to occur 3. Indivs have good memories 4. Altruists interact in symmetrical situations. |
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Life history is an organism's...
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life-time pattern of growth, differentiation, storage and reproduction.
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List some important life history traits
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Size at birth
Age at maturity Size at maturity Number of reproductions Clutch size |
Nat sel can act on any of these traits to improve fitness.
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How can LH traits evolve to maximize fitness?
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1. Higher survival through ages
2. Higher fecundity at each repro stage 3. Higher fecundity earlier in life 4. Longer repro lifespan 5. Earlier age of first repro. |
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Basic problem for Darwinian Demon?
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Resource allocation in a finite world
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-Survival, maintenance
-Growth -Reproduction. |
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Why do orgs age and die?
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Nat'l selection should oppose senescence and death, but it doesn't.
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2 theories:
1. Rate of Living theory 2. Evolutionary theory |
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Rate of living theory of aging
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Aging is caused by the accumulation of irreparable damage to cells and tissues (repl error and metabolic by-products).
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What are the predictions in the Rate of Living theory of aging?
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1. Aging rate correlated with metabolic rate
2. Species should not be able to evolve longer life spans because already selected for maximal repair |
Data does not support the age/metabolic rate correlation.
-Lifetime energy expenditure does vary -Possible to increase life-span with artificial selection. |
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Aging due to cumulative effects of cell division?
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Cells only capable of a limited number of divisions based on telomere length
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Jury still out on this hypothesis
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Evolutionary theory of aging
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Probability of survival and advantage of maintaining and repairing somatic tissues declines with age. Aging not due to cellular damage so much as failure to repair damage later in life.
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The Evol Theory of Again states that
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Genes that negatively affect repro or survival at later stages of life are only weakly selected against.
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Aging is due to:
1. Deleterious mutations - mutation accumulation 2. Trade-offs between repair and reproduction. |
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Genes reducing survivorship and reproduction
1. Early in life... 2. Late in life... |
1. early in life are strongly selected against
2. late in life are weakly selected against |
e.g. DNA mismatch repair enzyme.
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Antagonistic Pleiotropy hypothesis
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a trade-off and aging relationship
-aging is caused by alleles with pleiotropic effects that are advantageous early in life and deleterious later in life |
e.g. D. methuselah homozygotes live 35% longer BUT trade-off in that they have fewer progeny.
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Phenotypic plasticity
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When selection favors different phenotypes at different times, characters can adjust.
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