Evo Bio Midterm 2

Question 1

Isogamy vs. Anisogamy

Answer 1

Isogamy: All gametes are the same size
Anisogamy: Gametes are size-dimorphic (only gametes of different sizes can fuse)

Question 2

Anisogamy: Gamete Sizes

Answer 2

Large Gamete - Female
Small Gamete - Male
Large (Female) and Small (Male) Gametes - Hermaphrodite (most plants are likely hermaphrodites)

Question 3

The Two-Fold Cost of Sex

Answer 3

Sexuals produce offspring at half the rate of asexuals
- each parent in sexual reproduction is responsible for 2 offspring
- the asexual parent produces an average of 4 offspring –> reproduction increases faster because not producing males that are required to reproduce sperm

In theory, asexuals should rapidly take over any population. However, the benefits of sex essentially prevent this from happening.

Question 4

The advantages of sex (recombination)
–> the two hypotheses

Answer 4

1) Recombination facilitates the removal of deleterious mutations by selection
2) Producing offspring that differ from their parents is adaptive in variable environments

Question 5

Accumulating beneficial mutations: Asexuals vs. Sexuals

Answer 5

Asexuals: Two beneficial mutants can be incorporated into the population only if the second occurs in a descendant of the individual in which it first occurred

Sexuals: On the other hand, in a sexual population, the various mutations can get into the same individual by recombination –> therefore, individuals can accumulate different mutations more quickly

Question 6

Linked Loci and Selection

asexual reproduction

Answer 6

Linked loci interfere with each other’s response to selection

Without recombination, linkage facilitates the spread of deleterious mutations through a population (deleterious mutations can hitchhike with the beneficial ones)

Selection will find it difficult to pick the beneficial allele when its so close to the deleterious one

Question 7

“Least loaded class”

Answer 7

Carrying the least amount of harmful mutations

Question 8

(Asexual reproduction)
Why does the fittest clone eventually accumulate deleterious mutations?

Answer 8

In an asexual population, if the zero-mutation group is lost by chance, it’s gone forever –> no longer individuals that can possess 0 mutations

Question 9

Muller’s Ratchet

Answer 9

The absence of recombination (especially in an asexual population), results in an accumulation of irreversible deleterious mutations

this muller is so ratchet that it can’t even recombine

Question 10

Conditions that favor asexual reproduction

Answer 10

No deleterious alleles exist

Question 11

How does sex break Muller’s ratchet?

Answer 11

Re-creates the zero-mutation class through recombination

Question 11

Muller’s Ratchet: Genetic load

Answer 11

Decrease in fitness due to deleterious mutations increases over time

Question 12

Conditions that favor sexual reproduction

Answer 12

Decrease in mutations
Can create offspring that don’t have deleterious alleles

Question 13

Bet-hedging

Answer 13

When the environment is unpredictable, producing variable offspring increases the chance that some survive

sex is beneficial -> range of offspring produced (generates variation) -> will at least produce one offspring that will match the environmental background

Question 14

Host-parasite coevolution

Answer 14

Parasites evolve to target common host genotypes.
Sex (recombination) produces rare genotypes. Therefore, offspring of sexuals less likely to be susceptible to parasites than asexuals

Question 15

Sexual Selection

Answer 15

Differential reproductive success due to variation among individuals in success at getting mates

Other words: Selection that arises from differences in mating success

X-axis: Trait
Y-axis: Mating success

Question 16

Sexual Selection and Natural Selection

Answer 16

Sexual selection often opposes natural selection because some traits increase mating success but decrease survival

Question 17

What causes sexual selection?

Answer 17

One sex is more mate-limited than the other.

Question 18

Operational sex ratio

Answer 18

The ratio of reproductively active males to females

When there are more reproductively active females, more males will get mates but not all females

Question 19

Reproductive success: Heavily vs. lightly investing

Answer 19

Heavily Investing Parent –> resource/time limited
“female” -> intersexual selection –> choosy, can’t afford to mate with many

Lightly Investing Parent –> mate limited
“male” -> intrasexual selection –> compete for mates

Question 20

Differences in mating success: strength of sexual selection

Answer 20

Larger differences in mating success among males –> stronger sexual selection in males

Smaller differences in mating success among females –> weaker sexual selection in females

Question 21

When sexual selection is stronger in one sex, we can predict…

Answer 21

1) The sex subject to strong sexual selection will compete for mates [often but not always males]
2) The sex subject to weak sexual selection will be choosy (often but not always females)

Question 22

Intersexual selection

Answer 22

Between-sex (female) choice
Differential mating success due to mate choice

1) pre-existing sensory bias
2) direct benefit of resources
3) indirect benefits “good genes hypothesis” -> ext. Hamilton-Zuk hypothesis

Question 23

Intrasexual selection

Answer 23

Within-sex (male-male) competition
Differential mating success due to competition with members of the same sex

1) combat traits (alt. mating strategies can lead to disruptive selection)
2) sperm competition (race vs. raffle)
3) mating displays

Question 24

Combat traits

Answer 24

Used within-sex competition (intrasexual selection)

Question 25

What sperm traits contribute to fertilization success?

Answer 25

Number of sperm (if sperm competition is a raffle) Sperm length (if sperm competition is a race)

Question 26

Sperm Competition: Prediction and Hypothesis

Answer 26

External fertilizers: Raffle Internal fertilizers: Race Internal fertilizers, sperm competition should drive the evolution of motility traits like length Internal fertilizers have longer sperm - Sperm length is a sexually selected trait driven by sperm competition

Question 27

What underlies preference for showy displays?

Answer 27

Pre-existing sensory bias Direct benefits: resource acquisition Indirect benefits: better genes for offspring

Question 28

Pre-existing sensory bias

Answer 28

Selection on avoiding predators, finding food, etc. make females more responsive to certain cues Female preference evolves first (for something other than mate choice) and male displays follow

Question 29

Sensory bias in Trinidadian guppies

Answer 29

Female preference for male orange coloration might be driven by pre-existing foraging preference for orange food

Question 30

Direct benefit of acquiring resources

Answer 30

In many species, males provide food, parental care, or some other resources If females can distinguish between males who provide more vs fewer resources, choosy females will do better than non-choosy females Larger gift (that male provides female) = longer copulation --> Longer copulation = more sperm transferred

Question 31

Indirect benefit of better genes for offspring

Answer 31

Displays may indicate genetic quality If individuals with better displays carry genes associated with higher fitness, the other sex will benefit from being choosy "good genes" hypothesis

Question 32

Indirect benefit of better genes for offspring: frog chirping example

Answer 32

Long-calling males produced offspring that grew faster and were more likely to survive than short-calling males

Question 33

Hamilton-Zuk hypothesis

Answer 33

Animals choose mates for genetic disease resistance, based on costly displays that only healthy individuals can afford to produce Individuals with showy displays were less likely to have parasites

Question 34

Cryptic Female Choice

Answer 34

Cryptic female choice (CFC) refers to post-mating female preferences that bias fertilization towards the sperm of specific males, or, alternatively, that favor or disfavor the zygotes produced with sperm of specific males

Question 35

Sexual dimorphism

Answer 35

Not all sexual dimorphism is caused by sexual selection In some cases, sexual dimorphism is the result of natural selection

Question 36

Why cooperate with relatives?

Answer 36

Kin selection and the evolution of altruism

Question 37

Altruism

Answer 37

The actor suffers a cost; the recipient receives a benefit

Question 38

Why did altruism seem like a fatal problem for the theory of evolution?

Answer 38

Individuals with a certain trait will have a lower fitness. Therefore, natural selection should eliminate this trait, but it doesn't.

Question 39

Kin selection

Answer 39

Selection could favor a trait that decreases an individual's fitness if it increases the survival and reproductive success of close relatives Why? Relatives share genes — the behavior of an individual toward others can influence the success of the actor's genes acts on INDIVIDUALS

Question 39

Reproductive altruism

Answer 39

An extreme form of altruism Some individuals forgo reproduction to help relatives reproduce Ex: Slime molds Although stock cells do not undergo reproduction, their altruistic behavior allows the spore cells to reproduce

Question 40

Individuals should act to...

Answer 40

Maximize their inclusive fitness!

Question 41

Inclusive fitness

Answer 41

Direct fitness + indirect fitness Direct fitness = an individual's own reproductive success Indirect fitness = additional reproduction by relatives made possible by an individual's actions

Question 42

What are the conditions under which altruistic behavior evolves?

Answer 42

Hamilton's rule The benefit to the recipient (B) is much larger than the cost to the actor (C) The recipient is a close relative (high r)

Question 43

Hamilton's rule

Answer 43

Br - C > 0 B = benefit to the recipient r = relatedness between actor and recipient (0-1) --> the larger the R, the larger the weighted benefit C = Cost to the actor

Question 44

Calculating relatedness: the probability of identity by descent

Answer 44

Full siblings: r=1/2 Half-siblings: r=1/4 Cousins: r=1/8

Question 45

When are families likely to adopt another relative?

Answer 45

Adoptions only happened when the indirect fitness benefit outweighs the direct fitness cost. When the benefit is very high (Closely related) or if the cost is very low (mom doesn't have any many pups)

Question 46

How can cooperation evolve between non-relatives?

Answer 46

Reciprocity and Group selection/ multilevel selection

Question 47

Reciprocity

Answer 47

Actor incurs a fitness cost now in exchange for a future fitness benefit

Question 48

Group selection

Answer 48

A relationship between a group's phenotype and group fitness

Question 49

Multi-level selection

Answer 49

Selection acting at multiple levels (on individuals and on groups)

Question 50

Group selection gradient

Answer 50

X-axis: group trait y-axis: group fitness

Question 51

Cooperation

Answer 51

If cooperators benefit their social groups, cooperation can increase in frequency in the population as a whole, even if it decreases in frequency within groups within groups, selfish individuals have higher fitness than cooperators but groups with more cooperators are more productive (in groups with more cooperators, all individuals have higher fitness) --> therefore, groups with cooperators produce more offspring selection favoring cooperators among cultures > selection against cooperators within cultures

Question 52

What is life history evolution all about?

Answer 52

Tradeoffs How to allocate a finite pool of resources (eg survival, growth, reproduction)

Question 53

Why do organisms age and die?

Answer 53

Mutation accumulation and antagonistic pleiotropy

Question 54

Mutation accumulation hypothesis

Answer 54

Late-acting deleterious mutations are weakly selected against The effective population size for late-acting mutations is smaller than for early-acting mutations --> selection is weaker on late-acting mutations and drift is stronger (also because Ne dies) Deleterious alleles should be at higher frequency than early-acting deleterious alleles

Question 55

The antagonistic pleiotropy hypothesis

Answer 55

Alleles conferring early benefits and late costs can be adaptive - More individuals will experience the early benefit than pay the late cost SELECTION favors an early-life benefit at the expense of a late-life cost Early life benefit helps organism to survive and reproduce, so when they experience a late-life cost, they have already reproduced,

Question 56

Extrinsic mortality

Answer 56

Non-age related mortality (eg predation) the rate of extrinsic mortality influences the rate of senescence

Question 57

Will individuals age more rapidly when extrinsic mortality is high or when extrinsic mortality is low?

Answer 57

When it's high! High extrinsic mortality favors early reproduction and weakens selection on aging. Low extrinsic mortality favors later reproduction.

Question 58

Infectious disease vs. non-communicable disease

Answer 58

infectious disease: an illness caused by a (micro)organism -> bacteria, fungus, virus, parasite non-communicable: an illness not caused by another organism --> heart disease, stroke, cancer, autoimmune disease, genetic disorder

Question 59

relative to their hosts, parasites and pathogens tend to have...

Answer 59

Larger population sizes, rapid generation times

Question 60

Virulence

Answer 60

The damage done by a parasite to its host

Question 61

Why are some pathogens more virulent than others?

Answer 61

Coincidental evolution hypothesis: pathogen virulence isn't a target of selection itself, but an accidental byproduct of selection on another trait (e.g. tetanus) Short-sighted evolution hypothesis: traits that enhance pathogen fitness within hosts decrease transmission between hosts Tradeoff hypothesis: Virulence can be favored by selection if killing its host increases the pathogen's chances of being transmitted (example of evolution favoring maximum virulence)

Question 62

Why would pathogens that are more likely to kill their host be more likely to transmit?

Answer 62

Rapid within-host reproduction = increased transmission A pathogen cannot reproduce inside its host without harming it --> to reproduce, pathogens steals energy and nutrients from the host, and/or produce toxic metabolic wastes

Question 63

Prediction with Tradeoff hypothesis

Answer 63

Selection favors parasites that reproduce more quickly within their hosts — until the parasites begin to harm the hosts so severely that they kill their host before transmission

Question 64

What does slower transmission favor?

Answer 64

Less virulent pathogens — cannot risk killing new host before finding another one to infect It is when pathogens have a shorter time to transmit, they are more virulent

Question 65

Transmission mode + Prediction

Answer 65

Direct transmission requires a mobile host Vector- or water-borne transmission does not Prediction: Vector-borne diseases should be more virulent than directly transmitted diseases

Question 66

What does the pathogen's fitness depend on?

Answer 66

Its transmission rate! Therefore, it doesn't care if they kill their host but only if it transmits to another host

Question 67

Why does antibiotic resistance (bacteria strains being resistant to antibiotics) decline when antibiotics aren't used?

Answer 67

Antibiotic resistance has a cost, so resistant strains have lower fitness (cost of resistance) than sensitive strains in the absence of the antibiotic

Question 68

Costs of resistance

Answer 68

Tradeoff between antibiotic resistance and another function (eg growth rate) Detectable as lower fitness of resistant pathogens when the antibiotic is not present --> loss-of-function mutations: the loss of function itself --> gain-of-function mutations: the expense of maintaining new genes and proteins

Question 69

If there's a cost to resistance, what will happen to the ratio of sensitive:resistant bacteria in the absence of antibiotic?

Answer 69

Sensitive strain will increase over evolutionary time

Question 70

Compensatory mutation

Answer 70

A subsequent mutation that eliminates the cost of resistance Therefore, over many generations, the sensitive strain should have no advantage anymore (eg a mutation that eliminates the tradeoff between resistance and growth rate) and the resistant strain will overcompete the sensitive strain

Question 71

Herd immunity

Answer 71

Some people cannot be vaccinated: Babies, pregnant women (some vaccines), immune-compromised people Herd immunity is the only thing protecting them

Question 72

Pathogens: Antibiotics vs. Vaccines

Answer 72

pathogens rapidly evolve resistance to antibiotics but not to vaccines vaccines: administered before infection, multiple immune responses, low effective population, broad immune pressure drugs: after infection, one site, high effective population, specific mechanism to be selected

Question 73

Why do pathogens rapidly evolve resistance to antibiotics but not to vaccines?

Answer 73

Timing of action antibiotics: administered therapeutically (large pathogen population size) vaccines: administered prophylactically (small pathogen population size) antibiotics: takes only 1 resistance mutation to evolve resistance to an antibiotic vaccine: takes many resistance mutations to evolve resistance to vaccines

Question 74

How to minimize antibiotic resistance?

Answer 74

Make antibiotics more like vaccines --> increase the number of mutations required to evolve resistance Minimize antibiotic use --> allow cost of resistance to eliminate resistant strains

Question 75

What is the unit of selection in a tumor?

Answer 75

A cell

Question 76

Cancer and Multicellularity

Answer 76

Cancer represents a breakdown of multicellular cooperation Multicellularity --> requires cooperation among cells for the development, maintenance and reproduction

Question 77

Four forces of evolution, applied to cancer

Answer 77

Mutation -> novel alteration of the genome Natural selection -> differences in fitness among cells with different phenotypes Gene flow (migration) -> the movement of cells between tissues (metastasis) Genetic drift -> random change in allele frequencies

Question 78

Proto-oncogenes vs. oncogenes

Answer 78

proto-oncogenes: genes that control the rate of cell division oncogene: mutated versions of proto-oncogenes that disrupt control of cell growth and division

Question 79

Larger-bodied animals and Cancer

Answer 79

Larger-bodied animals should be more likely to get cancer, because they undergo more cell divisions

Question 80

Cancer: Multi-level selection

Answer 80

Selection at the level of cells favors proliferation - Natural selection is short-sighted - Immediate fitness gains for cancer cells drive the evolution of increased cell division and metastasis Selection at the level of individual organisms favors cancer suppression

Question 80

Cancer and Viruses

Answer 80

Rather than viruses killing their host cells, they accelerate the rate of cell division to produce more viruses

Question 81

p-53: tumor-supressor protein

Answer 81

prevents cancer, but accelerates senescence deficient p53 activity --> survival will decrease because they are more likely to develop cancer elevated p53 activity --> most likely no cancer but mice suffer high tissue damage and end up dying early

Question 82

Genetic Drift and Cancer

Answer 82

Because tumor cell populations start out small, the fate of many mutations is governed by drift (random survival of that one cancer cell) --> means that many mutations that appear in tumors are neutral (unrelated to cancer phenotypes)

Question 83

Why is cancer so hard to treat?

Answer 83

The cancer cells are you! Like antibiotic resistance in bacteria, cancer cells that acquire mutations that allow them to resist chemotherapy grow faster than susceptible cancer cells

Question 84

Coevolution

Answer 84

Reciprocal evolutionary change between interacting species, driven by selection

Question 85

Why does coevolution often cause extremely rapid trait evolution?

Answer 85

Each trait is both the target and agent of selection

Question 86

Arms race

Answer 86

Coevolution between two species that causes escalating trait changes in both species More common with host-predator relationships Graph: Directional change in resistance

Question 87

Why can't every organism be highly resistant to something?

Answer 87

Because resistance is costly. E.g. Garter snakes and TTX Snakes that are less resistant have a high muscle force. Snakes that are more resistant have a low muscle force.

Question 88

Convergent evolution and toxins

Answer 88

Snakes that eat TTX-bearing amphibians around the world have convergently evolved TTX resistance.

Question 89

Red Queen coevolution

Answer 89

Common in host-parasite coevolution Parasites target common host genotypes Rare resistance alleles have a fitness advantage Parasite-host relationships

Question 90

Time shift experiments

Answer 90

Using time travel to test coevolutionary hypotheses Using resistance to today's organism in comparison to another organism back in time/present day Arms race: directional change in resistance --> snakes from further back in the past would be less and less resistant to today's newts Red Queen: cycles of resistance -> some snakes from the past would would be just as resistant to today's newt as snakes from the present

Question 91

Red Queen coevolution: Matching Alleles Model

Answer 91

When allele of parasite matches allele of host --> parasite can infect the host

Question 92

Parasite-Host allele graph

Answer 92

X-axis: Generation Y-axis: allele frequency No new resistance mutations forming in red queen -> fitness is a function of which allele is more common (makes this different from arms race)

Question 93

Red Queen coevolution with predatory-prey cycles in ecology

Answer 93

In ecology, changes in population size through time. Traits are (usually) treated as a fixed property of a species. In evolution, change in inherited traits (allele freq) of a population through time

Question 94

Plant traits and pollinators

Answer 94

Pollinators and flowers are remarkably well matched/plant traits have been shaped by coevolution with pollinators - Flower Color (red with hummingbirds/white with moths/bats) - Floral smell - Female mimicry in orchids (plant looks like a female fly so more males want to mate with it)

Question 95

Is caffeinate nectar an adaptation to improve pollinator memory of floral rewards?

Answer 95

Maybe. But these data aren’t sufficient to test that hypothesis Caffeine also deters herbivores, because it’s bitter. Alternative hypothesis: Caffeine leaks into nectar. Its effect on pollinators is a byproduct of coevolution between plants and herbivores

Question 96

Mutualism

Answer 96

Benefits of mutualism also have a cost of providing goods and services (time, resources) Benefit must be larger than the cost

Question 97

Plant-microbe mutualisms

Answer 97

Model systems for studying mutualism's costs and benefits

Question 98

Microbial Mutualisms: Cost

Answer 98

Up to 20% of a plant's carbon budget goest to rhizobia (use light energy to convert carbon dioxide from the atmosphere into fixed carbon)

Question 99

Under what condition (s) will a mutualism break down?

Answer 99

If the cost increases and the benefit decreases

Question 100

In industrial agriculture, synthetic nitrogen fertilizer is added to the soil. Does nitrogen fertilizer influence the benefit or cost of the rhizobia mutualism for the plant?

Answer 100

It decreases the benefit of mutualism because the plant no longer needs the nitrogen these bacteria provide in order to grow

Question 101

Legume: rhizobia

Answer 101

Root nodule houses nitrogen-fixing bacteria called rhizobia (fertilizer factories) Nitrogen: benefit for legume / cost for bacteria Carbon: cost for legume / benefit for bacteria

Question 102

Indirect Benefit: Fischerian

Answer 102

Ignores viability (health of the partner) Ornamentation (trait to attract mates) evolves due to preference Preference persists as by-product "I find that attractive" "I'll make that then"

Question 103

Indirect Benefit: Condition Dependent

Answer 103

Only high viability males can make ornamentation Females want healthier males

Question 104

Indirect Independent

Answer 104

Not related to viability Different from Fischerian because female preference evolves independently

Question 105

Hill-Robertson Interaction

Answer 105

Deleterious mutation link to another locus

Question 106

As genetic relatedness increases...

Answer 106

Benefit to cooperation increases

Question 107

Viruses + Solution

Answer 107

Transmit more --> But... if it doesn't replicate, it'll run out of copies fast Replicate more --> But...then it might kill the host and cannot transmit 1) Don't transmit using hosts: use water or vectors (can replicate more) 2) Replicate as much as possible without killing the host tradeoff hypothesis x

Question 108

Bacteria: Pros and Cons of Resistance

Answer 108

If no resistance: Pro: No costs. Con: You probably die. If resistance: Pro: You don't die. Con: You take a fitness cost (this is why resistance goes down without antibiotics). They can evolve to compensate. Phage therapy takes advantage of this.

Question 109

Halfwerk et al. 2018 "Tungara frogs paper"

Answer 109

Male frogs in urban environment had more conspicuous (standing out) calls Less predators -> less negative selection Less mating -> more desperate Females were more attracted to urban frog calls -> urban frogs were also flexible between environments

Question 110

Jones and Ratterman 2008

Answer 110

Mate choice is essential to mechanisms of sexual selection Bateman gradient x-axis: # of mates y-axis: # of offspring male: directional line (competition, needs more mates for reproduction isn't resource-heavy, doesn't care about good quality offspring) female: plateau (resource-heavy, won't produce as many offspring because investing)

Question 111

Kramer and Meunier

Answer 111

Mainly address controversies between group selection and kin selection

Question 112

Tarpy et al. 2004

Answer 112

Test of group vs. kin selection: 2 mechanisms by how new queens are made Queen Rearing: workers could favor related queens, KIN SELECTION "nepotism" Queen Elimination: best queen wins = best for entire hive, MULTILEVEL SELECTION Findings: No, worker bees prioritize best-quality queen regardless of relatedness --> supports broader arguments for multi-level selection

Question 113

Eusociality: 3 Major Pillars

Answer 113

Mutual Care of Offspring, Overlap of Generations, Reproductive Division of Labor