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bio120 > Lec 9 slides and reading > Flashcards

Lec 9 slides and reading Flashcards

1
Q

why do different species that coexist in the same locality remain distinct?

A

do not interbreed

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2
Q

lack of interbreeding

A

reproductive isolation

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3
Q

geographical variation

A

Tendency of populations of the same species to differ according to their geographical location, often in ways that are clearly adaptive → geographical variation

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4
Q

importance of molecular evolution and divergence between different species

A

allows biologists to make inferences about the relationships between different species

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5
Q

what would happen if there were no barriers to interbreeding b/w members of different species?

A

diversity of life could not exist

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6
Q

what happens when barriers to interbreeding between formerly separate species have broken

A

highly variable offspring are produced

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7
Q

main barrier that prevents related species from interbreeding

A

Sometimes main barrier is a simple difference in habitats or in the time of breeding of the species

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8
Q

barriers from interbreeding in plants

A

In plants, there’s a characteristic brief flowering time each year, and species with non-overlapping flowering times will be unable to interbreed

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9
Q

barriers from interbreeding in animals

A

In animals, the use of different breeding sites can prevent individuals from different species from mating with each other
Subtle features of organisms(can only tell from species’ history), prevents individuals from different species from mating (even if in same place)
E.g. there may be an unwillingness to court individuals of the other species because they don’t produce the right smell or sound

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10
Q

behavioral barriers

A

Behavioural barriers to mating are obvious in many animals, and plants have chemical means of detecting pollen from the wrong species and rejecting it

Even if mating takes place, sperm from wrong species may be unsuccessful in fertilizing female eggs

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11
Q

hybrids and fertility

A

Even when hybrids are viable, they are often sterile, and don’t produce offspring that can pass genes onto future gens (mules→hybrid b/w donkey and horse)

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12
Q

complete inviability or sterility of hybrids

A

isolates the 2 species

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13
Q

evolution of barriers to interbreeding

A

Most barriers to interbreeding between species are by-products of evolutionary changes that occurred after the populations became isolated from each other by being geographically or ecologically separated

E.g. Darwin’s finches, if a small amount of individuals fly across to island and establish a new pop, the new and ancestral populations will evolve independently of each other

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14
Q

effect of genetic drift on population

A

Under the processes of mutation, natural selection and genetic drift, the genetic compositions of the 2 populations will diverge
These changes will be promoted by differences in the environments experienced by the populations, to which they become adapted
E.g. Food plants available to a seed-eating species of bird differ from islands, and even members of the same species of finch differ in beak sizes→ differences in food abundance

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15
Q

geographical variation

A

The tendency if populations of the same species to differ according to their geographical locations (in ways that are adaptive) → geographical variation
E.g. physical differences between races (skin pigmentation)

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16
Q

migration

A

In a species that consists of a set of local populations, there is some migration of individuals between different locations
Amount of migration varies between organisms
If migrant individuals can interbreed with members of the population in which they arrive, they will contribute their genes to this population

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17
Q

what type of force is migration

A

Migration → homogenizing force, opposing the tendency for local populations to diverge genetically by selection or genetic drift

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18
Q

true or false: population will diverge from each other, depending on AMOUNT of migration and evolutionary forces promoting differences b/w local populations

A

true

Populations of a species will diverge more or less from each other, depending on the amount of migration, and on the evolutionary forces promoting differences between local populations
Strong selection can cause even adjacent populations to differ
E.g. copper mining produces contaminated soil with metals which are toxic to plants → creates metal tolerant plants

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19
Q

how do gradual changes in traits arise during migration?

A

Gradual geological changes in traits arise because migration blurs the differences caused by selection that varies geographically, in response to changes in environmental conditions

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20
Q

Differences between geographically separate populations of ____ species don’t require different types of selection

A

the same

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21
Q

true or false:
Same selection can sometimes lead to different responses

A

true

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22
Q

Differences between populations of the same species can also evolve even if there’s no selection at all, as a result of …

A

the random process of genetic drift

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23
Q

Despite the visible differences between the major races, humans have _________ barriers to interbreeding between different populations or racial groups

A

no biological

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24
Q

Some cases where populations at opposite ends of a species range have diverged so much that…

A

they can’t interbreed→ if intermediate become extinct, they would be considered different species

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25
Q

The origin of reproductive isolation between a pair of geographically separated populations is not surprising if…

A

there have been independent evolutionary changes in 2 populations

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26
Q

Each alteration in the genetic composition of one population must either be _________, or must __________________ that it can spread by genetic drift

A

favoured by selection in the population; have a slight effect on fitness

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27
Q

how is hybrid sterility produced

A

Hybrid sterility is produced by interactions between different genes from the 2 species

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28
Q

Once 2 related populations have become completely isolated from each other by barriers to interbreeding, their evolutionary fates will be independent of each other and tend to …

A

diverge over time
One cause of divergence is natural selection; closely related species often differ in many structural/behavioural characteristics that adapt them to their way of life
Sometimes, there are few evident differences between related species

29
Q

fossil record

A

In the fossil record, many examples of lineages showing little or no change over years, followed by abrupt transitions to new forms
Intense selection can produce changes in a trait over 100 gens or less
Traits WON’T change greatly, once a species living in a stable environment has had time to adapt to it
Usually impossible to tell from the fossil record whether an observed ‘sudden’ evolutionary change implies the origin of a new species (which can’t interbreed with its ancestor(progenitor)) or involves a simple lineage evolving in response to environmental changes

30
Q

What do species mean where there’s asexual reproduction in single-celled organisms?

A

Similar species, cluster together in regard to the characters that are used, are classed as the same species, whereas other groups of individuals that form a different cluster are assigned to different species

31
Q

molecular evolution and mammals

A

More distantly related mammals (carnivores and rodents) differ at the sequence level much more than do different primates

32
Q

how do most changes to the amino acid sequence of a protein impair its function to some extent

A

A small effect caused by a mutation → selection→eliminates mutation from pop.
Most mutations that change protein sequences therefore never contribute to evolutionary differences in gene sequences that accumulate between species
Some amino acid sequence evolution is driven by selection acting on occasional favourable mutations, so that molecular adaptation occurs

33
Q

Silent changes to sequences of genes often have …

A

little to no effect on biological functions
Makes sense that most divergences in gene sequences between species are silent changes
When a new silent mutation appears in a population, it’s a single copy among millions of copies of the gene

34
Q

How does a mutation spread through the pop. if it doesn’t have any selective advantage to its carrier?

A

Random changes in the frequencies of alternative variants (genetic drift) take place in finite populations
E.g. in the fruitfly, for the pop. to be maintained→both adults must contribute 2 descendants to next gen→ if pop varies in eye colour with some carrying a mutant gene that makes eyes bright red, while non-mutant version makes eyes normal dull red → if individuals with either type of gene have same average number of offspring→no selection on eye colour→ neutral in its effects
Because of this neutrality, genes of next generation will be drawn randomly from parental population

Some individuals may have no offspring, while others may have more than the average of 2 offspring → means the frequency of the mutant gene in the progeny gen won’t be the same as its frequency among the parents

Over the gens, there will be continual random changes in composition of pop until either all members of pop have the gene for bright red eyes or else it’s lost from the population and they have the alternative version of the gene

In a small pop→ genetic drift is fast→ won’t take long until all members of pop become the same

35
Q

genetic drift

A

Genetic drift→ change in frequency of an existing gene variant in pop. due to random chance (diagram shows example with traits of fruitfly)

36
Q

2 effects of genetic drift

A

While a new variant is drifting to loss or to a frequency of 100%, the character affected by gene is variable within pop.
-The input of new neutral variants by mutation and the changes in variant frequencies by drift determine the variability in the pop.

Selectively neutral variant that’s initially rare has some chance of spreading throughout the whole pop. and replacing alternative variants

37
Q

what can genetic drift lead to

A

Genetic drift leads to evolutionary divergence between isolated populations, even without any selection promoting the changes (very slow process)
Rate depends on rate at which new neutral mutations arise as well as rate at which genetic drift leads to replacement of one version of a gene by a new one

38
Q

if no selection is acting on pop…

A

If no selection is acting, nothing affects the number of mutational differences between a pair of species except the rate at which mutations appear in the sequence and the amount of time since the species’ last common ancestor

39
Q

mutation rate determines rate of…

A

divergence

40
Q

Neutral changes accumulate in a gene as time goes on, at a rate that depends on…

A

the gene’s mutation rate

41
Q

Rates of morphological changes depend strongly on …

A

environmental change and variable rates and reversals of direction can occur

42
Q

why do protein sequences evolve slower than silent DNA differences

A

Protein sequences evolve slower than silent DNA differences, and are useful for comparing species that diverged a while ago
Between species, multiple changes will have occurred at some sites in their DNA sequences→ becomes hard to count number of mutations

43
Q

sources of microevolution

A

natural selection, genetic drift, mutation and migration

44
Q

taxonomic(or morphological) species concept

A

based primarily on distinct measurable differences

45
Q

biological species concept

A

based on inter-fertility among individuals

46
Q

species defined by darwin

A

species defined as groups of organisms that are sufficiently similar in phenotype

47
Q

what is a species

A

a group of interbreeding natural populations that are reproductively isolated from other such groups

48
Q

key to distinguishing species

A

reproductive isolation

49
Q

biological species concept further

A

-focuses on the process (reproductive isolation)
-geographic isolation alone is not sufficient
-isolation does NOT have to be absolute
-must be possible interbreeding in the wild
-doesn’t apply for bacteria, asexuals, highly self-fertilizing species or fossils

50
Q

what does the biological species concept not apply for

A

-doesn’t apply for bacteria, asexuals, highly self-fertilizing species or fossils

51
Q

where does speciation occur

A

-often called geographic speciation
-due to involvement of geographical isolation
-allopatric speciation much more common and easier to evolve

52
Q

allopatric speciation

A

Definition: Allopatric speciation occurs when a population is divided into geographically isolated groups, leading to the development of reproductive barriers over time. The separation can be caused by PHYSICAL barriers like mountains, rivers, or distance.

Process:
Geographic Isolation: A population is split by a geographical barrier.

Genetic Divergence: The isolated populations experience different environmental pressures and mutations, leading to genetic differences.

Reproductive Isolation: Over time, these genetic changes can result in reproductive barriers (e.g., differences in mating behaviors, timing, or physical incompatibilities).
Examples:

Darwin’s finches on the Galápagos Islands, where different islands have populations that evolved independently.
The formation of new species of squirrels in the Grand Canyon due to the physical barrier of the canyon itself.

53
Q

sympatric speciation

A

Definition: Sympatric speciation occurs when new species arise from a single population while inhabiting the same geographic area. This can occur without physical barriers and often involves behavioral, temporal, or ecological factors.

Process:

Same Habitat: Populations remain in the same area but exploit different ecological niches.
Reproductive Isolation: Differences in behavior, mating preferences, or timing can lead to reduced gene flow between subgroups within the population.
Genetic Divergence: Over time, these differences can accumulate, resulting in speciation.
Examples:

Cichlid fish in African lakes, where various species have evolved from a common ancestor, occupying different ecological niches (e.g., feeding at different depths).
Apple maggot flies, where a shift from hawthorn to apple trees has led to reproductive isolation based on host preference, despite living in the same area.

54
Q

pre-zygotic reproductive isolation barriers

A

-finding a compatible mate and mating
-fertilization

55
Q

post-zygotic reproductive barriers

A

-development and growth of zygote (f1)
-adult survival and reproduction (f1)
-growth, survival and reproduction of offspring (f2)

56
Q

reproductive isolating barriers

A

pre-zygotic barriers prevent mating or fertilization so no zygote is formed
-geological, ecological
-temporal, behavioural (mate recognition)
-mechanical (genital structure compatibility)
-cellular (sperm-egg compatibility)

57
Q

pre-zygotic isolation in apple maggot flies: habitat and temporal isolation

A

-host shift after arrival of domesticated apples in 1800s
-differences in timing of host plant fruiting (apple vs. haw)
-different timing of fly mating on preferred host plant
-reduces fly gene flow by 94% in sympatry (same region)

58
Q

how do apple maggot flies display sympatric reproductive isolation

A

-shift from hawthorn to apple trees has led to reproductive isolation based on host preference, despite living in the same area.

59
Q

post-zygotic barriers effect

A

-prevent proper functioning of zygotes once they’re formed
-caused by combinations of genes with low fitness in the hybrid
-arise as an indirect byproduct of evolution acting separately in different populations (can’t be directly favoured by natural selection)

60
Q

intrinsic post-zygotic barriers

A

inviability, sterility or abnormal development of hybrids

61
Q

extrinsic post-zygotic barriers

A

ecological mismatch of hybrid phenotype to environment

62
Q

example of intrinsic post-zygotic isolation

A

mule or hinny (sterile hybrid b/w horse and donkey)

63
Q

relation b/w genetic distance and post-zygotic isolation in fruit flies

A

-the more that fly pairs are genetically differentiated, the more likely they are to be reproductively isolated
-genetic distance is a measure of the degree of genetic differentiation between samples

64
Q

example of extrinsic post-zygotic isolation

A

poorly adapted hybrids
-aposematic heliconiu butterflies
-adaptation–> poisonous

-hybrids have colour patterns but predators dont recognize new warning colours of hybrids
-higher predation risk
-lower mating success

65
Q

is adaptive evolution required for speciation?

A

-local adaptation by different populations can lead to reproductive isolation and speciation
-distinct evolutionary responses to diff
selective pressures
-local adaptation not necessary, but
accelerates pop. divergence and evolution
of reproductive isolation

-called ecological speciation

66
Q

ecological speciation

A

adaptation to different things speeding up evolution

67
Q

local adaptation can generate ____ for reproductive isolating mechanisms

A

selection

68
Q

as populations diverge genetically (as a result of evolutionary forces - mutation, genetic drift, NS), they become…

A

reproductively isolated
-often as an incidental byproduct of
evolutionary change within populations

69
Q

reproductive isolation allows what to occur?

A

speciation
-populations continue evolving and adapting independently, driving macroevolutionary diversification

bio120 (19 decks)

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