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BIOL 2322 Ecology > Lecture 5: Evolution > Flashcards

Lecture 5: Evolution Flashcards

1
Q

Define microevolution

A

Occurs when there is a change in the allele frequency in a population over time/generations

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2
Q

Define adaptation

A
  1. An inherited trait that improves an individual’s ability to survive and reproduce in a particular environment
  2. the process of evolutionary change that occurs in response to natural selection
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3
Q

Define evolutionary fitness

A

the number of offspring an individual produces over its lifetime

So, the more offspring produced = the greater number of favourable alleles passed on = the greater fitness

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4
Q

Define macroevolution

A

process of change above the species level

ex. speciation or extinction

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5
Q

What are the 2 major sources of genetic variation?

A
  1. mutations

2. sexual reproduction

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6
Q

How does sexual reproduction lead to genetic variation?

A
  1. random fertilization
  2. independent assortment of chromosomes during meiosis
  3. crossing over of DNA between chromosomes during meiosis mixes paternal and maternal alleles
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7
Q

Define mutations

A

a change in allele frequency due to random changes in alleles that are caused by mutagenesis or DNA copying errors

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8
Q

What can occur if there’s a mutation on an individuals germ line?

A

the mutation will be passed onto the individual’s offspring and can increase within the population

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9
Q

Why are mutations not the best source of genetic variation?

A

It is rare that mutations are actually beneficial, most are harmful or neutral

Then natural selection also has to favour the mutation for it to become more common within a population

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10
Q

Define natural selection

A

A change in allele frequency in a population as a result of differential survival and reproduction caused by individual interaction with the environment

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11
Q

What are the 3 conditions required for natural selection to cause evolutionary change?

A
  1. Phenotypic variation must exist within the population
  2. The variation must be heritable
  3. The variation must cause a difference in survival and reproductive success
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12
Q

What are the 3 types of natural selection?

A
  1. directional selection
  2. disruptive selection
  3. stabilizing selection
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13
Q

Define directional selection and give an example

A

natural selection that causes the average expression of a phenotype to shift to an extreme
- ie., one extreme phenotype is favoured

ex. beak depth in medium ground finches shifted to larger sizes (extreme) as a result of the La Nina drought

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14
Q

Define disruptive selection and give an example

A

Occurs when natural selection pushes the average phenotype expression towards both extremes
ie., either extreme phenotype is favoured

ex. spadefoot tadpoles
- omnivores no more likely to die (extreme)
- carnivores more likely to survive (extreme)
- intermediates more likely to die
the mean was shifted towards both larger jaws/shorter intestines AND smaller jaws/longer intestines

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15
Q

Define stabilizing selection and give an example

A

Reduces variation around the mean to maintain the average phenotype expression

ex. Snow geese hatching dates
- hatching strategy is to have eggs all hatch around the same time to have protection in numbers
- those that hatch too early or too late will be more vulnerable to prey
- over time, less variation in hatch time makes the mean narrower and causes less variation

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16
Q

Which of the 3 types of natural selection spreads out the range of variation?

A

disruptive because it shifts the mean to two extremes

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17
Q

What is the consequence of selection?

A

adaptation

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18
Q

What is the only mechanism of evolution that consistently results in adaptation?

A

Natural selection

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19
Q

T or F: adaptation produces ideal organisms

A

FALSE. it produces organisms that are WELL SUITED to their environment but never produces ideal organisms

because there are constraints on adaptation

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20
Q

What are the 4 constraints on adaptation?

A
  1. selection can only act on existing variation
  2. new alleles arise through RANDOM mutation
  3. environments change
  4. adaptations are compromises and require trade-offs
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21
Q

Describe what is meant by trade-offs

A

Organisms have limited time and energy to allocate to different traits and have to make trade-offs between adaptations

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22
Q

What is a classic example of a trade-off?

A

Producing many small eggs vs few large eggs

Producing many small eggs will divide energy up into many organisms but numbers increase chance that at least one will survive

Producing few large eggs allows all the energy to give the best chance of survival to a few offspring

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23
Q

What are the 2 mechanisms of evolution?

A
  1. Gene flow (migration)

2. Genetic drift

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24
Q

Define gene flow

A

A change in allele frequencies as a result of individuals or their gametes moving into or out of populations

Can increase beneficial, disadvantageous, or neutral alleles in a population

25
Q

T or F: gene flow/migration will increase beneficial alleles and decrease disadvantage alleles

A

FALSE.

It can increase beneficial, disadvantageous or neutral alleles

26
Q

Does migration/gene flow increase or decrease genetic variation WITHIN populations?

A

Increase because there is new alleles coming into the population from other populations

27
Q

Does migration/gene flow increase or decrease genetic variation BETWEEN populations?

A

Decrease because populations will become more similar as alleles move from one population to another

28
Q

Define genetic drift and list the 2 types

A

A change in allele frequency due to random chance

  1. Bottleneck effect
  2. Founder effect
29
Q

Describe the founder effect

A

A type of genetic drift that occurs when a small group of individuals is split from the parent population

The small group = founder group, will contain alleles from the parent group in different frequencies

30
Q

Will the founder effect result in a separated group that is more or less genetically diverse than the parent group?

A

Less because the founder population will be much smaller than the parent population

if there is a common allele in the parent group, the probability that most of the individuals in the founder group have that allele is high

if there is a rare allele in the parent group, the probability that an individual in the founder group has it is low

31
Q

Describe the bottleneck effect

A

A type of genetic drift that occurs when a population rapidly decreases in size due to a random event and causes a change in allele frequencies

Generally happens after overhunting, major geological events, catastrophic events

32
Q

Will the bottleneck effect result in a population that is more or less genetically diverse than the original population?

A

Less because only a small percentage of individuals from the original population will survive so the less common alleles are more likely to disappear

33
Q

Does genetic drift increase/decrease beneficial, disadvantageous, and/or neutral alleles in a population? why?

A

Genetic drift can INCREASE beneficial, disadvantageous or neutral alleles in a population because the change is RANDOM

34
Q

When are the effects of genetic drift the most significant? why?

A

In small populations because there are already less copies of each allele

35
Q

Does genetic drift increase or decrease genetic variation WITHIN populations?

A

Decrease because alleles can be lost or fixed (when there is only one allele for a gene)

36
Q

Does genetic drift increase or decrease genetic variation BETWEEN populations?

A

Increase because it is random so the chances of the allele frequencies being the same in different populations is really low

37
Q

Define phenotypic plasticity

A

The ability of a single genotype to produce multiple phenotypes

38
Q

When is phenotypic plasticity beneficial?

A

In environments that vary often over time or space

39
Q

What are the 2 types of phenotypic plasticity?

A
  1. developmental plasticity

2. acclimation

40
Q

Define developmental plasticity

A

IRREVERSIBLE variation in phenotype arises among individuals with the same genotype early in development

41
Q

Define acclimation

A

REVERSIBLE change in phenotype that occurs in response to environmental changes

typically physiological changes

42
Q

How does phenotypic plasticity evolve?

A

When a phenotype has high fitness in one type of environment and low fitness in another type

43
Q

Define plastic genotypes

A

Genotypes that produce different phenotypes that will experience relatively high fitness in two different environments

44
Q

T or F: the average fitness across two different environments will be lowest for the plastic genotype?

A

FALSE. it will be highest

45
Q

How is plasticity tested?

A

By conducting reciprocal transplant experiments

46
Q

Describe reciprocal transplant experiments

A

Used to determine if phenotypic variation between populations is due to genetic differences or plasticity

Individuals are moved from each environment into the other and the phenotypes are measured and compared

47
Q

Describe a reciprocal transplant experiment with plants in wet and dry environments

A

study two populations of a plant species that grows in both wet and dry sites

  1. plant seeds harvested from wet site in the dry site
  2. plant seeds harvested from dry site in the wet site
  3. compare growth between 2 sites
48
Q

What can be concluded if the results of a reciprocal transplant experiment show significant change in mean height with transplant?

A

the plant height changes depending on the environment so the plant has phenotypic plasticity

49
Q

What can be concluded if the results of a reciprocal transplant experiment shows no significant change in mean height with transplant?

A

The genotypes are not plastic because the phenotype expressed was the same regardless of the environment

50
Q

Define speciation

A

the evolutionary process by which one species splits into two

51
Q

T or F: speciation occurs only with geographic isolation

A

False.

Speciation can occur with or without geographic separation

52
Q

What occurs as a result of speciation in regards to reproduction?

A

Speciation results in reproductive isolation which means that populations can no longer interbreed

53
Q

What are the two processes that speciation can occur by?

A
  1. allopatric speciation

2. sympatric speciation

54
Q

Define allopatric speciation

A

A physical separation of two populations creates a geographic barrier to gene flow between the populations

ex. mountain ranges rise, glacier develops, etc.

55
Q

How do the genetic differences that cause reproductive isolation arise between geographically isolated populations?

A
  1. genetic drift
  2. mutation
  3. differential directional selection (one side of the geographic barrier may favour one extreme phenotype and the other side may favour a different phenotype)
56
Q

Define sympatric speciation

A

Occurs when populations become reproductively isolated without a geographic barrier to prevent gene flow between them

57
Q

How do the genetic differences that cause reproductive isolation arise without a geographic barrier to gene flow?

A

Intrinsic reproductive barriers arise

  1. habitat barriers
  2. temporal barriers
  3. behavioural barriers
58
Q

What are the intrinsic reproductive barriers that arise to cause sympatric speciation?

A
  1. habitat barriers
    - different breeding habitat
  2. temporal barriers
    - different reproductive times
  3. behavioural barriers
    - different courtship or other mate recognition cues

BIOL 2322 Ecology (13 decks)

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