Biology 105 - Exam 3

Leafcutter ants perform a complex ballet of cooperative behaviors:

\- colonies with 10^6 workers

\- workers differ in size, form and have many specialized tasks

\- mother and many non-reproductive daughters

\- soldiers risk their life to defend the nest

\- farmers chop up leaves, use them to grow fungus and feed the colony

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Interaction types are defined by ___ .

the fitness effect on each partner

conflict

when the fitness interests of two individuals are different

cooperative

when one individual’s behavior benefits another

How can natural selection favor cooperation?

cheaters

“Cheaters” benefit from ____ .

the actions of others without providing benefits to them in return

If a cheater has high fitness in a population of cooperators, then _____ .

a mutation that causes individuals to cheat will spread, and cooperation can collapse

EX: cheaters - slime mold evolution under laboratory conditions

Why do individuals exhibit traits that increase the fitness of other individuals (rather than focusing all of their energy on improving their own fitness)?

1\. Group selection

2\. Direct benefits (byproducts)

3\. Reciprocity

4\. Altruism and kin selection

group selection

variation in reproductive success among groups

Group selected traits are beneficial to __ , not ______ .

the groups that bear them, individuals

Group selection was thought to be quite __ , and there are very __ verified examples.

rare, few

Individuals help others because they ultimately gain _ from their ___ .

direct benefit, cooperative behavior

Direct benefits (the cooperation) are a _____ .

byproduct of selfish action

EX: direct benefits/cooperation in herds - individuals in herds enjoy safety in numbers from predation

reciprocity

individual X takes on a cost to benefit Y, and Y, in turn, reciprocates that benefit to X

EX: reciprocity - vampire bats

\- live in unrelated groups and go foraging for blood meals at night

\- individuals will help feed their roost mates (through regurgitation)

\- if they fail to find food several nights in a row, they die

\- feeding of another individual is much more likely if they’ve \n received help from those individuals in the past

Models predict the conditions under which ____ is favored.

reciprocity

prisoner’s dilemma

each of two individuals will do best by acting selfishly, but if both individuals act selfishly, they will do worse than if they both cooperate

Game theory models show that selfish behavior is favored if ___ , but that repeated interactions can favor ____ .

individuals interact only once, cooperative behavior

Shared genes explain the evolution of ___ .

Altruism

altruism

cooperation with no direct benefit for the cooperator

EX: altruism - sterile worker bees help others in the hive and \n do not breed themselves

kin selection

selection on alleles that promote cooperative behavior with other individuals that share the same alleles (identical by descent)

To understand kin selection, we must examine the ____ .

fitness of alleles

**inclusive fitness** of an allele

its positive effect on the bearer of that allele (direct fitness) + the positive effect on related individuals that also share the same allele (indirect fitness)

Unlike other forms of cooperation, kin selection can only evolve among ____ .

members of the same species

The logic of kin selection is formalized in ____ .

Hamilton’s rule

Hamilton’s rule

an allele that causes an altruistic behavior will spread if the following condition is met: rB > C

**r**B > C

relatedness (when the allele is rare, r is the probability that the recipient of altruistic behavior also carries the allele)

r**B** > C

fitness benefit to the recipient

rB > **C**

fitness cost to the actor

**inclusive fitness** of an allele

rB-C

how to calculate relatedness

\- the autosomes of a diploid species, the alleles in a mother are related to those in her offspring, with r = 0.5

\- alleles in a given daughter are also related to those in her brothers and sisters, with r = 0.5

Inclusive fitness also explains the ____ .

evolution of spiteful traits

A behavior is **spiteful** if it _____ .

harms both the actor and the recipient

The conditions needed for spiteful alleles to spread:

\- the actor be less closely related to the recipient than to an average member of the population

\- harming the recipient enhances the fitness of other individuals in \n the population that are more closely related to the actor

Some interactions within families are the epitome of _ , while others are the most extreme forms of ______.

cooperation, conflict imaginable

eusociality

when some individuals do not reproduce and instead rear the offspring of others

sexually antagonistic selection

when a trait that is favored to increase in one sex is favored to decrease in the other

traits that often experience sexually antagonistic selection

\- mating frequency

\- parental care

mating frequency

males often benefit from mating when females don’t

parental care

selection favors offspring abandonment in the parent that pays the greater cost

infanticide

sometimes an individual’s fitness is enhanced by killing the young of its own species

EX: infanticide - male lions

male lions that take over a pride will kill all the infants in the pride to speed up the time to sexual receptivity in the females of the pride

EX: infanticide - female mice

female mice will kill some or even all of her young when resources are scarce, to save energy for future reproduction

parent-offspring conflict

when what is best for a parent conflicts with what is best for an offspring

Offspring can gain indirect fitness by ____ but often have even more to gain by ____ .

helping their siblings, increasing their own survival

Selection favors offspring that ____ , even if that ____ , so long as direct fitness gain _ indirect fitness loss.

take more resources from their parents, decreases the number of other offspring they have, >

Inclusive fitness favors parents that ____ , not divert extra resources to selfish ones.

maximize the number of offspring they have

The human placenta invades the mothers arteries and prevents them from ____ .

constricting

Human embryos have evolved to extract more resources from mothers than ____ .

mothers are favored to give

Natural selection can occur at ___ .

different levels of biological organization

natural selection

consistent differences in fitness among different classes of “individuals” (“individuals” need not be organisms)

Natural selection conflicts with ___ .

genic selection

Selfish DNA can spread in populations even if ____ .

decreases survival or reproduction

segregation distorters

mutations that cause an allele to have a greater than 50% chance of inheritance

transposable elements

short sequences of DNA that are able to insert additional copies of themselves in the genome

cytoplasmic male sterility

when a mutation inherited through the cytoplasm causes sterility

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Cytoplasmic male sterility in thyme plants illustrates ____ .

genetic conflict

Many biological phenomena result from ____ among organisms or among genes.

conflict or cooperation

Cooperation can evolve because it is __ for a group (rare), ____ to the actor, or based on ____ (reciprocity).

beneficial, directly beneficial, repeated interactions between individuals in which the fitness interests of the associates are aligned

Altruism can evolve by ____ .

kin selection

An allele’s inclusive fitness is the ___ .

sum of its direct fitness and its indirect fitness

Conflict and kin selection together affect the ____ .

evolution of many interactions among family members

Conflicts may exist among different genes in a species’ genome that are inherited by ___ .

different pathways

Every species is subjected to ____ from its ____ .

natural selection, biotic environment

coevolution

reciprocal genetic change in interacting species (EX: evolution in one species causes adaptive change in another species and vice versa)

Coevolution can occur in any ____ .

intimate species interaction

symbioses

intimate species interactions

For a focal species, coevolution may occur with other species that are its:

resources, competitors, enemies, and mutualists

resources

species that are eaten or used for habitat

competitors

competing for food, space, or habitat

enemies

predators, parasites, etc.

mutualists

species that provide fitness benefits

Commensalism & Amensalism will not result in ____ .

coevolution

Traits of one species can shape the traits of other species both in negative interactions, _____ , and positive interactions , ____ .

(predation, competition, parasitism), (mutualism)

EX: coevolution

Coevolution can lead to ___ in species intensely shaped by ____ .

extreme traits, other species

Mutualists can evolve over time to ____ .

match their partners extremely well

When Darwin saw the Orchid species Angraecum sesquipedale and its extremely long nectar spur, he predicted ____ .

the presence of a pollinator with an extremely long proboscis

Only later was the long-tongued Sphinx Moth discovered by ___ in ___ .

naturalists, Madagascar

Coevolution is reflected by ____ in extreme cases.

parallel diversification

Aphids are phloem-sucking insects that have bacterial symbionts ( ___ ) that provide the insect with the ____ ( ___ ) .

Buchnera, aminoacid, Tryptophan

The Buchnera bacteria are ____ among hosts, meaning that mother aphids ____ .

vertically transmitted, pass on their Buchnera symbionts to their offspring

Aphid and Buchnera phylogenies are ____ .

concordant

concordant

‘match’ reflecting speciation events that are shared between the coevolving partners

The nature and strength of interactions can ___ , affecting ____ .

vary, coevolution

EX: interaction affects coevolution - The Limber pine has specialized cones that reduce depredation by squirrels, but these cones are less favorable for the Clark’s nutcracker, a bird species that disperses the plant’s seeds

The selection that nutcrackers and squirrels exert on pines varies among populations

Interactions between enemies and victims include ___ , ___ , and ____ .

predators and prey, parasites and hosts, herbivores and host plants

Interactions of enemies and victims are often ___ because enemies can cause ____ .

unstable, extinction of each other’s populations

Interactions between enemies and victims can lead to ___ in which each species ____ and leads to ___ .

arms races, adapts in response to the other, extreme traits

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Predators, parasites, and herbivores evolve extraordinary _ to capture ___ .

adaptations, prey, infect hosts, and consume plants

Prey, hosts, and plants have elaborate ___ .

counteradaptations

EX: extraordinary adaptations of predators, parasites, and prey -

EX: prey defenses - mimicry (both Batesian and Mullerian)

mimicry

close resemblance of an organism (the mimic) to some different organism (the model) such that the mimic benefits from the mistaken identity

EX: prey defenses - diverse animals have evolved warning signals, sometimes species mimic warning signals

Batesian Mimicry

unprotected species (mimic) evolves to look like a protected species (model)