Evolution ( BI 445 - Oregon State University) Final

What is the Oparin-Haldane model of the origins of life?

"Preboitic soup"

What aspect of prebiotic synthesis was shown to be possible by experiments such as Stanley Miller's experiments in the 1950s?

What aspect of prebiotic synthesis was shown to be possible by experiments using the clay montmorillonite?

What is the RNA World Hypothesis?

In what way is a ribozyme similar to DNA, but also similar to protein?

Do self-replicating ribozymes currently exist in nature?

No - not to our knowledge.

Why is it important to the RNA World Hypothesis to determine whether ribozymes could be self-replicating?

Most efficient ribozyme, each round population of ribozymes evolves

What clues in the way RNA is used in modern cells hint that RNA may have an ancient role in cellular metabolism?

central role in current cell function and DNA stability

Why was the gene for small-subunit RNA particularly well suited for studies of the phylogeny of all living things? Do you think this gene is also useful for studying relationships among living mammals, such as for elucidating the family tree of humans, chimpanzees, and gorillas?

Strong purifying selection; conserved nucleotides

Describe LUCA.

Last Universal Common Ancestor

Compare and contrast the "Ring of Life Hypothesis", the "Chronocyte Hypothesis" and the "Three Viruses, Three Domain Hypothesis" for the origins of the three domains of life.

Ring: Euk info/storage/= arcahaen; euk metabolism = bacteria

Chrono: early euk engulfs archeans later becomes nucleus

Three V: virus diversity replaced RNA-genomes 3 times (per each domain)

State four types of social interactions and the relative cost and benefit to the actor and

recipient.

Mutual Benefit results in a benefit to both the actor and the recipient. Altruism results in a cost to the actor and a benefit to the recipient.

Selfishness results in a benefit to the actor and a cost to the recipient.

Spite results in a cost to both the actor and the recipient. Cost and Benefit refer to less or more reproductive success, respectively, and hence contribution of alleles to the gene pool.

What is altruism?

Altruism is a type of social interaction defined by and action reducing the actor's fitness while increasing the fitness of the recipient.

State the logic of why Natural Selection cannot account for the evolution of altruistic

behaviors.

According to Natural Selection, an allele will decrease in frequency if it is

associated with an individual having less reproductive success than others. Altruistic

behaviors decrease the reproductive success of the actor while increasing the reproductive

success of the recipient. Therefore, any 'altruistic alleles' should be selected against.

Describe the evidence that suggests communal breeding among greater anis could have

evolved because of mutual benefit.

Greater anis form mating pairs whom typically will

build a nest with one or two other, unrelated mating pairs. The social group will take turns

incubating the eggs, feeding the chicks and will work together as a mob to deter predators

from eating their eggs or chicks. Social groups of 3 mating pairs all had roughly equal

reproductive success, but greater success than a social group of 2 mating pairs. Mating

pairs that did not form a social group, but tried to nest alone, had no reproductive success.

The cooperation with in a social group resulted in actors and recipients both increasing

their direct fitness, hence mutual benefit.

Are alarm calls among Belding's ground squirrels altruistic? Explain your answer.

No and yes. Belding's ground squirrels use a whistle as an alarm call that a hawk is near

and a trill as an alarm call that a mammal predator is near. In the case of whistles, of the

squirrels killed by hawks, 2% were the actor (the squirrel giving the alarm call) and 28%

were the recipients. For whistle alarm calls, the actor benefits and the recipient has a cost,

so this social interaction is selfish. In the case of trills, of the squirrels killed by a

mammal, 8% were the actor and 4% were the recipients. For trill alarm calls, the actor has

a cost and the recipient benefits, so this social interaction is altruistic.

What is Hamiliton's rule?

Br - C > 0; an 'altruistic allele' can be maintained in a

population when the Benefit to the recipient is greater than the cost to the actor by an

amount proportional to the genetic relatedness between the actor and recipient. So if r =

1/2 (degree of relation between full siblings), than the Benefit must be more than twice as

much as the Cost.

How does Kin Selection potentially account for altruistic behaviors?

Kin Selection predicts that altruistic behaviors will be favored when the actor is genetically

related (kin) to the recipient. Although the actor has a decrease in direct fitness, if the

recipient has the 'altruistic allele', then the recipient's increased fitness (actor's indirect

fitness) is additive to the actor's direct fitness: both contribute the allele to the gene pool.

The sum of an actor's direct and indirect fitness is called inclusive fitness.

What is direct fitness and what is inclusive fitness?

Direct fitness is the reproductive

success of an individual. Inclusive fitness is the individual's direct fitness plus indirect

fitness. Indirect fitness is the increase in a relative's reproductive success due to the

actions of the altruistic individual.

Describe the evidence that adoptive parenting in red squirrels could have evolved

because of Kin Selection.

Kin Selection predicts that altruistic behaviors will be favored

when the actor is genetically related (kin) to the recipient.

Over the course of a 20 year study, 34 litters were orphaned that were near a lactating

female that was a potential adoptive mother. Adopting an orphan costs the actor (the

adopting mother), because the probability each of her own offspring will survive

decreases. However, if the recipient, the orphan, is genetically related to the actor, then the

behavior of adopting can be favored and evolve.

For 7 litters of the 34 litters, the potential adoptive mother was a genetic relative. For 27

litters, the potential adoptive mother was not a genetic relative and none of these 27

mothers adopted a kitten. Of the 7 genetic relatives, 5 adopted and 2 did not. For the 5

that adopted, the mother's estimated indirect fitness was equal to or greater than the cost of

adopting. For the 2 that did not adopt, the mother's estimated indirect fitness was less than

the cost of adopting. These results are consistent with the expectation of Kin Selection.

From an evolutionary perspective, why is there parent-offspring conflict?

The limit on reproductive success of a parent is different than an offspring. A parent's

reproductive success is limited by how many offspring survive. As a parent increases

investment in one offspring there is a cost of decreasing the probability other offspring will

survive. In contrast, an offspring increases its chances of survival the more nutrients it can

get from the parent. There is a cost in that the offspring is related to its siblings, and so

decreasing survival of siblings does decrease an offspring's indirect fitness, but the cost is

less than the parent's cost.

The result is the parental investment that maximizes the parent's reproductive success is

less than the parental investment a given offspring needs to maximize its reproductive

success, hence a conflict.

What is reciprocity? Give an example.

Reciprocity is an exchange, between two individuals, of favors that results in mutual

benefit, both the actor and receipt benefit. An example from lecture is the behavior of

baboons. Baboons groom each other and will provide support to one baboon against a

third baboon. Researchers found that if a baboon was recently groomed by another

baboon, the groomed baboon responds to the other baboon's threat grunt by moving

towards the grunt, presumably to provide the other baboon with support against a 3rd

baboon. The results suggest there is an exchange of favors: grooming in exchange for

support when confronting a 3rd actor.

What conditions favor evolution of reciprocity? Explain how each condition favors

reciprocity.

Reciprocity is likely to evolve when (1) individuals repeatedly interact, (2)

have many opportunities to exchange favors, (3) the actor and recipient both need favors

and can offer favors, and (4) individuals have a good memory.

Reciprocity has a risk to the actor in that a recipient may not return a favor. For reciprocity

to be stable, the actor and recipient need to develop a long-term relationship of exchanges

in which the recipient does routinely return favors. Repeated interactions results in many

opportunities to exchange favors, and developing trust that a favor will be returned

requires both individuals give and return favors. A good memory allows an individual to

keep track of many past exchanges and whether or not another individual returned favors

routinely.

How can multilevel selection explain the existence of altruistic traits that are directed

to non-kin?

Multilevel selection is when there is a difference in reproductive success

between groups. If a group with more altruistic individuals (cooperators) has greater

reproductive success than groups with less cooperators, then the frequency of cooperators

in the whole, combined population can be maintained and even increase in frequency.

Even though within a group selfish individuals have greater reproductive success than

cooperators, the greater allele contribution to the whole population by groups with

cooperators at higher frequency than selfish individuals offsets the individual reproductive

success of selfish individuals.

Describe an experiment that tests whether multilevel selection can account for an

increase in the frequency of a heritable trait that costs the actor but benefits the recipient

I would start with a test population that has variation among individuals in the degree to

which they cooperate: some cooperate at a cost, and others do not cooperate and gain a

benefit. I would then distribute the individuals into subgroups so that each subgroup had a

different frequency of cooperators: from 0.2 to 0.8. I would then measure the fitness of

each subgroup. I would set the 'ecological' conditions so that subgroup fitness increases as

a function of frequency of cooperators in a subgroup. Multilevel selection requires that

there is a difference in fitness between subgroups as a function of the frequency of

cooperators in the subgroup (or frequency of some other trait you suspect is influenced by

multilevel selection). After allowing each subgroup to reproduce, I would then mix all the

individuals into a single population and measure the frequency of cooperators in the whole

population.

What is sexual dimorphism? Give an explanation for why sexual dimorphism exists?

Sexual dimorphism is differences in traits between males and females of the same species. Sexual dimorphism likely exists because of asymmetry between the sexes in what limits their reproductive success. The sex that is limited by access to mates has selection acting on characteristics that increase access to a mate, while the other sex is not under such selection. For example, when males are limited in access to mates, any inherited traits that increase access to mates will be preferentially passed on to the next generation. Sexual dimorphism also requires sex-determining genes (or chromosomes) that are different in males than females. In mammals, males have a Y chromosome, but females do not.

What is parental investment?

It is the amount of energy and material a male or female allocates to producing gametes, to providing nutrients for embryonic development, and energy and time to caring for the offspring after birth. Parental investment also includes the energy and time involved in getting a mate.

What is the difference between male and female parental investment?

The amount of energy and time put into making sperm is typically very small fraction of the energy that goes into making an egg and ensuring its development. Males also typically put less time and energy into caring for the offspring.

What is the limit on female reproductive success that results from parental investment?

A female invests much energy and materials into making eggs and providing nutrients for offspring development, and energy, materials and time into caring for offspring. This parental investment results in female reproductive success being limited by her capability for number of eggs, time available to make multiple clutches or litters, and survival of her offspring.

What is the limit on male reproductive success that results from parental investments?

Males invest in a lit less gametes and offspring development that females, and invest a lot less time in raising offspring. A males capacity to make sperm, hence reproductive potential, is much greater that females, so is not limiting. As a result, male reproductive success is limited by number of mates.

How does parental investment relate to the strength of sexual selection?

The sex that invests less energy, materials, and time in gametes and care of offspring has reproductive success limited to access to mates. An individual that has more mates has greater reproductive success. The greater the differential is between individuals in reproductive success, the greater the degree of sexual selection; the heritable traits tied to gaining access to mates are passed to the next generation at a much higher frequency.

What are the behavioral consequences, for males and females of a species, when there are asymmetric limits on reproductive success?

The sex that is limited by access to mates tend to have metabolically expensive traits involved in competition, such as direct fighting or fighting over mating territory (intrasexual competition), or involved in courtship displays to attract the opposite sex (intersexual competition).

The sex that is limited by the capacity to make and raise offspring tends to be choosy about their mate. Choosiness often is for a partner that displays an extreme trait that requires access to energy and resources. Because it takes healthy genetics ('fit' alleles; low number of deleterious alleles) to succeed in acquiring the needed resources, the extreme trait signals to the female mating with the healthy individual will result in healthy offspring.

Use the concepts of evolution to provide an explanation of why the behavior of being choosy when picking a mate exists in some animals?

First, there must be some genetic basis to choosy behavior. Second, for the choosy behavior to be at high frequency among females (or males) of a species, choosy behavior must in some way lead to greater reproductive success than non-choosy behavior.

One possibility is that the male traits that attract a female require the male to have genetic information well adapted to the conditions of life. A female that mates with such a male will then pass those 'fit' alleles onto her offspring, which will then be more likely to survive, reproduce, and pass on the 'choosy' alleles as well.

Another scenario is more direct - females choose a male that provides resources, which can then be used to ensure offspring have plenty of nutrients during early development to increase their survival rate.

The two figures below show the size distributions of Galapagos Island Iguanas and the percent survival of Iguanas of the different size categories.

(a) Can Natural Selection explain why the most frequent sizes of Iguana are large?

(b) If not, then what is an alternative explanation for the high frequency of large Iguanas?

(a) No, the larger Iguanas have a lower survival rate so based on the expectations of Natural Selection, large iguanas should have lower reproductive success than Iguanas with a higher survival rate.

(b) For there to be a high frequency of large Iguanas, the 'large Iguana' alleles must be passed on to the next generation at least as often as the 'small iguana' alleles. Something must make up for the lost reproductive success due to lower survival. That something is likely greater access to mates. Larger Iguanas can chase other small Iguanas off preferred mating rocks.

Is sexual selection ever greater for females than males of a species?

Yes, when the reproductive success of females is limited by access to mates more so than males, then sexual selection is greater for females than males. An example is the broad-nosed pipefish. A female lays her eggs in the brood pouch of a male. The male fertilizes the eggs and provides oxygen and nutrients to the eggs until they hatch. The time ti takes for the eggs to develop is longer than the time it takes for a female to have another batch of eggs, so at any given time there are more females than males with available pouches. A female that can get multiple batches of eggs into multiple male brood pouches will have much more reproductive success than females that fail to entice a male to accept her eggs. Females do a courtship dance to entice males to accept her eggs.

How does migration between diverged populations increase the allelic diversity within the recipient population?

Calling two populations divergent meant the two populations have different allele frequencies, or even alleles not present in the other population. Gene flow to a recipient population therefore will bring missing alleles, so increasing the allelic diversity of the recipient population.

Consider the Island Model. In what way does persistent migration to the Island decrease the genetic differences between the mainland and island populations?

Persistent migration, or gene flow, from a mainland population to an island population results in the homogenization: the allele frequencies in the island population will change until being equal to the mainland population, so that there will no longer be genetic differences between populations.

Consider the conclusions of studies on the water snakes of Lake Erie. Assume that you spend two years watching the lake day and night and never see water snakes migrating from the mainland to the island. Yet, every month you see 4 banded snakes for every 1 unbanded snake being caught by prey.

Provide and explanation for the presence of snakes on the island.

If there is no migration, or gene flow, from a mainland population to an island population then a couple possible explanations are (1) frequency-dependent selection; as the banded snake population begins to decline maybe the unbanded snakes will become preyed upon more, or (2) the mutation rate creating banded alleles is high enough to maintain banded alleles in the population, or (3) maybe there is non-random mating happening so that banded females and banded males mate more frequently than unbanded snakes.

However, the selection and non-random mating explanations would be misguided, as it is known that banded snakes migrate to the islands.

Inbreeding is known to increase the frequency of deleterious recessive alleles and expose those alleles (more homozygous recessives), yet animal and plant breeders often maintain breeding lines with choice qualities by inbreeding also called 'line breeding'.

(a) why do you think breeders often use line breeding?

(b) how do breeders limit inbreeding depression?

(a) Breeders use line breeding to maintain uniformity and consistency of desired qualities among the pure bred offspring. If the pedigree of the parents that start the line show no signs of deleterious recessive alleles, then inbreeding will result in fit offspring as long as no new mutations introduce deleterious alleles.

(b) Breeders limit inbreeding depression by choosing the fit individuals for mating pairs. A pair that continuously produces offspring with no expected traits is likely to lack deleterious recessive alleles and it may take many generations before an unlucky mutation introduces a new deleterious allele into the breeding population.

Using population genetics terms, explain why the population of Florida Pumas continued to have low mean fitness even though their habitat was protected and slightly expanded.

Although some habitat was protected for the Florida Pumas, the population was small for numerous generations. Small populations are prone to evolve by genetic drift that results in random fixation of alleles, including deleterious alleles associated with lower fitness. Inbreeding also tends to increase in small populations.

What did conservation biologists do in the 1990s to help stop the population decline of the Florida Puma and how did this action help stop the decline?

Conservation biologists moved 8 female, Texas Pumas to Florida. Five of the females mated and produced >20 offspring. The Texas Pumas brought in 'lost' alleles, so the F1 offspring were heterozygous at many genetic loci and hence 'hid' the phenotypic effect of deleterious recessive alleles. As a result, the F1 offspring had greater fitness.

The coefficient of linkage disequilibrium can be used to detect positive selection, because neutral alleles do not show...

high allele frequency and high coefficient

Linkage disequilibrium will degrade most rapidly in population...

with short generation times and high rates of recombination

When alleles at a locus is in linkage disequilibrium with neighboring loci and it is in high frequency, we can infer that it is...

favored by positive selection

For genetic loci that are in linkage equilibrium, the product of allele frequencies predicts the haplotype frequencies.

True

Two adjacent genetic loci will always be in linkage disequilibrium if recombination between genetic loci is rare.

False - given enough generations (thousands), rare recombination will return the loci to linkage equilibrium. Also, rare or not, recombination does NOT cause disequilibrium.

What is linkage disequilibrium (LD)? And what are two mechanisms that casue LD?

Linkage disequilibrium is when there is a nonrandom association between specific alleles at different genetic loci: the haplotype (multilocus genotype) is at higher or lower frequency than predicted by the frequencies of the constituent allele. .

Selection against or for a haplotype cancasue LD. Population admixture, which is another word for migration into a population, or genetic drift can also cause LD.

What is a haplotype?

A haplotype is a specific combination of alleles at multiple genetic loci. A chromosome has a haplotype; a specific combination of alleles.

A diploid cell with two copies of a chromosome potentially has two haplotypes if the two copies are different with regard to the allele combination.

What is the connection between recombination and the number of different haplotypes in a population?

Recombination between genetic loci increases the number of different haplotypes until all possible allele combinations are present in the population.