Lesson 5: Types of Evolution

Question 1

what is speciation

Answer 1

when an evolution leads to the evolution of an entirely new species
- if evolution evolves so much to a point where a new species is formed, then its called speciation
- evolution itself is advancements of a species, not a changed or new species

Question 2

modes of speciation: reproductive isolation - what is it and how does it work

Answer 2

for a new species to form, individuals from the original species must evolve to become reproductively isolated from the remainder of the population
- the individuals in the species are no longer reproducing with one another
- becoming reproductively isolated with each other can lead to speciation

Question 3

what is a reproductive isolating mechanism

Answer 3

any factor that prevents two populations from interbreeding while in the same region

Question 4

what are the reproductive isolating mechanisms

Answer 4

prezygotic and postzygotic

Question 5

prezygotic- what is it and how does it work + examples

Answer 5

these are mechanisms that prevent fertilization and zygote formation
- examples: differences in breeding season, physical or behavioural traits, habitat preferences, or incompatibility of gametes

Question 6

postzygotic- what is it and how does it work + examples

Answer 6

these are mechanisms that prevent a fertilized egg from growing into a viable adult
- examples: zygote mortality, hybrid individual inviability, or hybrid infertility

Question 7

prezygotic examples: behavioural isolation

Answer 7

different species use different courtship and other mating clues to find and attract a mate
(the presence and absence of specific behavioural mating calls to find a mate)
- male frogs of different species have unique calls that attract only females of their own species

Question 8

prezygotic examples: temporal isolation

Answer 8

different species breed at different times of the year
(prevents species from breeding because they breed at different times)
- pussy willows produce flowers in the early spring; they are reproductively isolated from plant species that produces flowers at a different time of year

Question 9

prezygotic examples: ecological isolation

Answer 9

very similar species may occupy different habitats within a region
(two species cant interbreed due to living in different environments/areas)
- the mountain bluebird lives at high elevations, while the eastern bluebird prefers lower elevations and does not encounter the mountain species

Question 10

prezygotic examples: mechanical isolation

Answer 10

differences in morphological features may make two species incompatible
(physical differences in reproductive systems and gentilia make it impossible to breed)
- male damselflies transfer sperm during an unusual mating flight; the male and female genitalia of each species are uniquely shaped and are physically incompatible with other species

Question 11

prezygotic examples: gametic isolation

Answer 11

male gametes may not be able to recognize and fertilize an egg of a different species
(gametes aka reproductive cells are not compatible and are unable to achieve fertilization)
- many marine animals including corals, clams, and sea cucumbers release their sperm and eggs into open water; the sperm recognize eggs of their own species through chemical markers on the surface of the eggs

Question 12

postzygotic examples: zygotic mortality

Answer 12

mating and fertilization are possible, but genetic differences result in a zygote that is unable to develop properly
- some species of sheep and goat are able to mate, but the zygote is not viable

Question 13

postzyotic examples: hybrid inviability

Answer 13

a hybrid individual develops but either dies before birth or, if born alive, cannot survive to maturity
- when tigers and leopards are crossed, the zygote begins to develop but the pregnancy ends in a miscarriage or stillborn offspring

Question 14

postzygotic examples: hybrid infertility

Answer 14

hybrid offspring remain healthy and viable but are sterile
- mules are the sterile hybrid offpsring of a horse-donkey cross

Question 15

modes of speciation: allopatric speciation

Answer 15

most new species form when a single species is seperating into two geographically isolated populations
- once populations are physically seperated, they cannot exchange genetic information so are reproductively isolated
- they will respond to their environment and will become less and less similar over time

Question 16

modes of speciation: sympatric speciation

Answer 16

a new species can also evolve from within a large population
- no geographic isolation is necessary
- this can happen gradually as a response to a change in the environment, or suddenly through a random mutation
- both species will inhabit the same geographic area but are genetically incompatible

Question 17

natural selection leads to what predictable outcomes? (according to the patterns of evolution)

Answer 17

• closely related species share many homologous/same features, even if they do not serve the same function
• species may have vestigal structures that once served as a function in their ancestors
• remote islands are inhabited by unique species that are descended from a few individuals who were able to reach the island

Question 18

types of evolution: adaptive radiation

Answer 18

this occurs when a single species evolves into a number of distinct but closely related species (each new species fills a different niche)
- this process most commonly occurs when a variety of new resources become available that are not being used by other species
- EX: darwins finches is a good example of this

Question 19

types of evolution: divergent evolution

Answer 19

this is when a group/closely related groups that share a common ancestor are placed under selective pressures and therefore evolve to occupy unique niches (due to the development of differences over time)

Question 20

what has divergent evolution allowed us to do?

Answer 20

it allowed us to develop such great biodiversity of life
- this is because all natural ecosystems require a number of species each with unique ecological roles
- EX: we need producers, consumers, decomposers, and scavengers to maintain balance with the ecosystem
- EX: rodents in ontario forests- all species (chipmunks, squirrels, beavers, etc) evolved from a single common ancestor but now show unique characteristrics and fill various niches in the ecosystem

Question 21

types of evolution: convergent evolution

Answer 21

this occurs when two different species or taxa evolve to occupy similar ecological niches
- similar adaptations may be favoured in very different geographic regions that have very similar selection pressures
- EX: sharks and dolphins have evolved streamlined bodies even though they are very distantly related
- KEY: similar features have evolved in very distantly related organisms which has allowed for them to occupy similar niches (unlike what we looked at in divergent evolution)

Question 22

types of evolution: coevolution

Answer 22

when a species evolutionary success is closely linked to that of another species
- EX: certain plants have evolved hard protective shells to protect their seeds while birds developed stronger jaws and teeth for chewing through those same hard shells
- symbiotic relationships are good examples of coevolution

Question 23

what extreme cases can occur in coevolution?

Answer 23

species can become so closely dependent that the extinction of one species could lead to the extinction of the other

Question 24

RECAP: divergent evolution

Answer 24

two or more species diverge from a common ancestor
- they share a common ancestor but evolved into two different species

Question 25

RECAP: convergent evolution

Answer 25

two or more distinct species share traits NOT due to a common ancestors
- EX: birds, butterflies, and bats- they all have wings that allows them to fly but they don’t share a common ancestor with wings, so each one evolved to have wings independently; evolution converged on a similar trait in vastly different species

Question 26

RECAP: reproductive isolation

Answer 26

meaning two populations of the same species can no longer mate together successfully

Question 27

RECAP: prezygotic

Answer 27

type of isolation that happened between groups of the same species before an egg even got fertilized
- Behavioral isolation: when species can have different behaviors, even very slight differences, that can isolate them; EX= birds having different songs
- Temporal isolation: species could breed at different seasons, years, even different times of the day- they may look very similar, but if they don’t have the same breeding season, then you’re going to have an isolation
- Habitat isolation: you can have two species living in the general same area but if one prefers an aquatic environment and one prefers a terrestrial environment, that will be a habitat isolation

Question 28

RECAP: allopatric speciation

Answer 28

when one species diverges into two new species because of geographic isolation
- there is a geographic barrier that separates the populations; while natural selection is acting on these populations, there is also some geographical barrier- like a river, or mountain that keeps them from being able to interbreed and share the same gene pool

Question 29

RECAP: sympatric speciation

Answer 29

the speciation that happens in the same area

Question 30

RECAP: postzygotic

Answer 30

sometimes offspring that are produced between two different species are very weak and do not survive long
- Sometimes if species interbreed, the offspring is NOT able to develop in even very early embryonic stages because there is a genetic incompatibility