Lec 9 slides and reading

Question 1

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

Answer 1

do not interbreed

Question 2

lack of interbreeding

Answer 2

reproductive isolation

Question 3

geographical variation

Answer 3

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

Question 4

importance of molecular evolution and divergence between different species

Answer 4

allows biologists to make inferences about the relationships between different species

Question 5

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

Answer 5

diversity of life could not exist

Question 6

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

Answer 6

highly variable offspring are produced

Question 7

main barrier that prevents related species from interbreeding

Answer 7

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

Question 8

barriers from interbreeding in plants

Answer 8

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

Question 9

barriers from interbreeding in animals

Answer 9

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

Question 10

behavioral barriers

Answer 10

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

Question 11

hybrids and fertility

Answer 11

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)

Question 12

complete inviability or sterility of hybrids

Answer 12

isolates the 2 species

Question 13

evolution of barriers to interbreeding

Answer 13

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

Question 14

effect of genetic drift on population

Answer 14

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

Question 15

geographical variation

Answer 15

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)

Question 16

migration

Answer 16

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

Question 17

what type of force is migration

Answer 17

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

Question 18

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

Answer 18

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

Question 19

how do gradual changes in traits arise during migration?

Answer 19

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

Question 20

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

Answer 20

the same

Question 21

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

Answer 21

true

Question 22

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

Answer 22

the random process of genetic drift

Question 23

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

Answer 23

no biological

Question 24

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

Answer 24

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

Question 25

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

Answer 25

there have been independent evolutionary changes in 2 populations

Question 26

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

Answer 26

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

Question 27

how is hybrid sterility produced

Answer 27

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

Question 28

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 ...

Answer 28

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

Question 29

fossil record

Answer 29

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

Question 30

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

Answer 30

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

Question 31

molecular evolution and mammals

Answer 31

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

Question 32

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

Answer 32

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

Question 33

Silent changes to sequences of genes often have ...

Answer 33

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

Question 34

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

Answer 34

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

Question 35

genetic drift

Answer 35

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

Question 36

2 effects of genetic drift

Answer 36

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

Question 37

what can genetic drift lead to

Answer 37

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

Question 38

if no selection is acting on pop...

Answer 38

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

Question 39

mutation rate determines rate of...

Answer 39

divergence

Question 40

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

Answer 40

the gene’s mutation rate

Question 41

Rates of morphological changes depend strongly on ...

Answer 41

environmental change and variable rates and reversals of direction can occur

Question 42

why do protein sequences evolve slower than silent DNA differences

Answer 42

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

Question 43

sources of microevolution

Answer 43

natural selection, genetic drift, mutation and migration

Question 44

taxonomic(or morphological) species concept

Answer 44

based primarily on distinct measurable differences

Question 45

biological species concept

Answer 45

based on inter-fertility among individuals

Question 46

species defined by darwin

Answer 46

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

Question 47

what is a species

Answer 47

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

Question 48

key to distinguishing species

Answer 48

reproductive isolation

Question 49

biological species concept further

Answer 49

-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

Question 50

what does the biological species concept not apply for

Answer 50

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

Question 51

where does speciation occur

Answer 51

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

Question 52

allopatric speciation

Answer 52

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.

Question 53

sympatric speciation

Answer 53

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.

Question 54

pre-zygotic reproductive isolation barriers

Answer 54

-finding a compatible mate and mating -fertilization

Question 55

post-zygotic reproductive barriers

Answer 55

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

Question 56

reproductive isolating barriers

Answer 56

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)

Question 57

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

Answer 57

-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)

Question 58

how do apple maggot flies display sympatric reproductive isolation

Answer 58

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

Question 59

post-zygotic barriers effect

Answer 59

-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)

Question 60

intrinsic post-zygotic barriers

Answer 60

inviability, sterility or abnormal development of hybrids

Question 61

extrinsic post-zygotic barriers

Answer 61

ecological mismatch of hybrid phenotype to environment

Question 62

example of intrinsic post-zygotic isolation

Answer 62

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

Question 63

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

Answer 63

-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

Question 64

example of extrinsic post-zygotic isolation

Answer 64

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

Question 65

is adaptive evolution required for speciation?

Answer 65

-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

Question 66

ecological speciation

Answer 66

adaptation to different things speeding up evolution

Question 67

local adaptation can generate ____ for reproductive isolating mechanisms

Answer 67

selection

Question 68

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

Answer 68

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

Question 69

reproductive isolation allows what to occur?

Answer 69

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