L7 Natural selection and adaptation

mutation

ultimate source of varitation

In a population that has three alleles at locus A (A1, A2, A3) the frequency of allele is 0.4 and the frequency of allele A3 is 0.5 what is the frequency of allele A2

0.1

what do these equations calculate?

A) p + q = 1

B) p² + 2(pq) + q² = 1

A) allele frequency of parents, B) genotype frequency of offspring

Brown fur allele B is dominant to the grey fur allele b. In a population of 100, 75 have brown fur. what is the Allele frequency of b? assume the population is in HW equilibrium

0.3

0.5

0.7

0.25

0.5

p² = B = 0.75

q² = b = 0.25

allele frequency is sqrt 0.25

Though important for some highly social species, cultural evolution is not a major contributor to evolutionary change. Why?

• not all species have culture

• culture can be variable within species

• culture is not consistent across species

• culture does not have a genetic component

culture does not have a genetic component

Evolution by natural selection occurs only traits are

• disadvantageous

• heritable

• advantageous

• advantageous in a certain environment

Heritable

What is natural selection

differential reproductive success (fitness) of biological entities that differ in one or more characteristics

1. variation in phenotype

2. differential fitness associated

3. heritability of phenotypes

evolution and natural selection

evolution by natural occurs when heritable variations leads to change in populations over generations

natural selection is not synonymous with evolution

change in allele frequency in allele frequencies over time

evolution is change in allele frequency in a population over generations

not number of alleles

Natural selection leads to non random changes in allele frequency

Natural selection and Chance

Natural selection is the nonrandom change in allele frequency over time

other processes cause evolutionary change through chance changes allele frequency

How are neutral alleles affected by selection

• Neutral alleles are not affected by selection

• Neutral alleles will increase through selection, but only if they are beneficial

• Neutral alleles will increase by selection only in certain environments

• Neutral alleles will decrease by selection, because they are not beneficial

Neutral alleles are not affected by selection

• they don’t affect fitness

levels of selection

genes

cell types

individual organisms

populations (highly controversial)

Biological fitness

survival and reproductive success

gene fitness

more copies of that allele in the next generation

copies of gene (allele) in the next generation

selfish genetic elements

fitness of gene does not (necessarily) contribute to fitness of the organism the gene is in

• wants to be reproduces as often as possible, often at the detriment of organisms the gene is found in

  • eg transposable elements

meiotic drive/segregation distortion

this occurs when selfish genetic elements segregate into gametes more than expected by segregation

individual fitness

number of offspring in the next generation

• occurs at a higher level than selection among genes

• however, this can still be considered at a genic level

• when an individual experiences reproductive success at least half of their genome is being passed to the next generation

selfish gene hypothesis

fitness at the individual level only serves to propagate the alleles associated with that fitness

Altruism - a fitness conundrum

altruistic behaviors are those that benefit another individual, often at the expense of their own fitness

if altruistic behaviors decreases personal fitness, so how does it evolve

evolves by kin selection

Kin selection

occurs by increasing kin fitness

and individual is increasing the fitness of the alleles that they share with that relative

this reinforces the idea of the selfish gene

group fitness

survival of population to the next generation

group selection

proposes that one population as whole can be more fit than another population of different genetic compostition

Group selection was originally proposed to what

explain altruistic behavior

• though individual cheaters have greater fitness, but altruistic population have a greater fitness as a whole

sometimes altruism doesn’t win

this is because individuals selection works much faster than group selection and therefore has a much stronger evolutionary force

it is agreed that group selection

has little impact on evolutionary change

How does kin selection allow for altruism to evolve?

• selection is acting on the alleles: alleles than make you altruistic have pleiotropic effects that also make you super fertile.

• selection is acting on the individual: the individual who is altruistic is more likely to have higher fitness.

• selection is acting on the alleles: related individuals share alleles and when one individual experiences fitness, their shared alleles experience fitness

• selection is acting on the individual: individuals who sacrifice for others are protected by the group and get access to more resources

selection is acting on the alleles: related individuals share alleles and when one individual experiences fitness, their shared alleles experience fitness

multilevel selection theory

adaptation is the process

by which, over time, organisms are altered to become better suited to their environmenst - this process is natural selection

an adaptation is a characteristic

that makes organisms better suited for their environment that evolved through natural select

adaptations _____ arise through natural selection; natural selection does ______ result in adaptations

always; not always

Exaptation/preadaptation

adaptation of an existing structure for a different, completely new, adaptive function

many evolve from nonadaptive traits

exaptation vs adaptation

exaptation:

• feather evolves an adaptive function other than the original function

• not all birds with wings can swim = unique function

adaptation:

• a new trait evolves an adaptive function

• wings have evolved into unique structures (flippers) for new adaptive function

selection for

selection for a trait implies the feature caused the organism to have higher fitness

the functio of this trait is to incraese fitness

selection of

selection for one trait often causes incidental selection of another trait

the increase of this trait is a side effect or selection for the correlated trait (hitch hiking)

Recognizing adaptations

not every trait is an adaption

a trait could be

1. a consequence of physics or biochemistry

2. evolved by another mechanism (eg. genetic drift)

3. correlated with an adaptation (selection of vs for)

4. a consequence of phylogenetic history

for this reason, we should not assume a trait is an adaptation unless we have evidence to support this conclusion

The long sharp beak of the kea evolved for cracking seeds. As the kea spent more time exposed to humans it began to use this same beak (no modification) to pick flesh from livestock and wreak all kinds of havoc in human populations.

In this instance the beak of the kea is considered

• an adaptation (and nothing more)

• an exaptation/preadaptation

• none of the above. the beak is not adaptive in this instance.

an exaptation/preadaptation

Which of the following is an example of an exaptation/preadaptation

• Cats evolved retractable claws from non-retractable claws, helping them hunt more efficiently.

• Angiosperm use modified leaves, called flower petals, to attract pollinators

• The giraffe's long neck evolved via male-male competition (sexual selection). They now use their long necks to feed from taller vegetation.

• Cacti thorns are modified leaves that serve to protect the cacti from herbivory and reduce water loss.

The giraffe's long neck evolved via male-male competition (sexual selection). They now use their long necks to feed from taller vegetation.

Trade-off

existence of both fitness benefit and fitness cost for a specific trait

can also be though of as a compromise between two traits that cannot be optimized simultaneously

natural selection is constrained by what

genetic variation

without heritable variation, new and potentially beneficial traits cannot arise and be selected for

lack of genetic variation also explains the retention of non-adaptive traits

which of the following is a fitness trade-off

• In some hornbill species, the male helps seal the female in a tree with her nest until the young are ready to fledge.

• Hummingbirds are the best pollinators of certain flowers, but bees are the best pollinators for orchids.

• The strong, thick beak of a woodpecker helps it find insects in trees.

• Turtle shells provide protection but are heavy and burdensome when moving.

Turtle shells provide protection but are heavy and burdensome when moving.