Species amp Speciation Speciation Gradual process in which one population separates from another AND builds up enough genetic differences to become a new species CONTENT SUMMRY Species amp Speciation ID: 485949
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Slide1
Evolution lesson 4
Species & SpeciationSlide2
Speciation
Gradual process in which one population separates from another.
AND builds up enough genetic differences to become a new species.Slide3
CONTENT SUMMRY:
Species & Speciation.
Reproductive isolating mechanisms
Pre-zygotic.
Post-zygotic.
Examples of Speciation.
Grasses.
Darwin’s Finches.
Polyploidy in Plants.
Hybrids.
Types of Selection
Stabilizing.
Disruptive.
Directional
Human Impact on Evolution – Polar Bears, Climate Change, & Hybrids.Slide4
Biodiversity threatened
Example: giant panda
Protect some species’ existence
Stop evolution of new species (ex: bacteria resistant)Slide5
Define Species:
One or more populations of individuals.
Can interbreed under natural conditions.
And produce fertile offspring.
That are reproductively isolated from other such populations.
CAN produce fertile offspring.
ONLY WITHSlide6
When does Speciation happen?
When changes in allele frequencies occur that are significant enough
To mark the formation of a new species
Distinct from the parental species.
How did divergence/change in allele frequency happen?
Last lesson: mutation, selection, genetic drift.
Barrier to reproduction
P
reventing inter-breeding
between 2 closely related species.Slide7
What’s the main POINT?!
Interbreeding happens
New species CANNOT form.
Interbreeding prevented
BARRIER in place
Speciation begins.
Different ways speciation occurs – will be mentioned later onSlide8
Speciation process began……
Command! DO THIS OR ELSE!
M
embers of NEW species are to AVOID MATING with members of the old.
I’m the Strong evolutionary pressure (Natural Selection) and this is my COMMAND
What happens if interbreeding (i.e. mating between different species) happened?
Because of genetics, the hybrid offspring produced are often less successful. They die early or produce few or no offspring.
PUNISHMENT (OR ELSE) –
Natural Selection punished individuals that accidentally mate outside their own species
How? They will leave fewer successful offspring.
You DISOBEYED ME… prepare to be PUNISHED!Slide9
SO that’s a waste..
Producing unsuccessful offspring – a waste.
Strong selection
pressues
– ensuring species mate with members of their own only.
Preventing interbreeding –
Reproductive barriers.
Geographical barrier
(physical separation)
Biological barrier
(genomes too different)Slide10
CONTENT SUMMRY
:
Species & Speciation.
Reproductive isolating mechanisms
Pre-zygotic.
Post-zygotic.
Examples of Speciation.
Grasses.
Darwin’s Finches.
Polyploidy in Plants.
Hybrids.
Types of Selection
Stabilizing.
Disruptive.Directional
Human Impact on Evolution – Polar Bears, Climate Change, & Hybrids.Slide11
Reproductive Isolating Mechanisms
Anything that PREVENTS successful reproduction from happening.
Important in speciation… why?
ALLOWS one species to diverge (i.e. separate) into two separate species.
TWO TYPES
Pre-zygotic
Post-zygoticSlide12
1) Pre-zygotic Isolating Mechanisms:
What’s a ZYGOTE? FERTILIZED EGG.
Pre-zygotic isolating mechanisms?
BARRIERS to
reproduction.
Occur BEFORE a zygote can
form.
Usually before mating.
Think about it:
2 populations can’t get together to mate.
Genes WON’T MIX
DIVERGE GENETICALLY
from each other more over timeSlide13
Pre-Zygotic isolating mechanisms:
Favored in evolution – because they are more efficient
Resources
are NOT wasted producing unsuccessful offspring
.
Several – can occur through differences in space, time, behavior, or breeding mechanisms.
Ways pre-zygotic isolation can occur:
Geographic Isolation.
Habitat Isolation.
Temporal Isolation.
Behavioral Isolation.
Mechanical Isolation.
Gametic
Isolation.Slide14
1) Geographic Isolation
Populations become isolated because of
physical barrier
.
Occurs very gradually.
Once speciation occurred, the two populations won
’
t be able to interbreed anymore EVEN if BARRIER is REMOVED.Slide15
2) Habitat Isolation
Two populations occupying different habitats
So they are less likely to meet and attempt to reproduce.
Commonly experienced by non-moving organisms (ex: Plants).
Common ancestor
Scarlet Oak
Black Oak
Closely related tree speciesSlide16
Occur in same ecosystem BUT occupy DIFFERENT HABITATS within it.
Speciation happened? YES
WHY? Because the two populations of the ancestral species began
occupying slightly different habitats.
SO? Over time each
became adapted to its own environment
(wet or dry).
Because of the physical separation, less chances their gametes would meet.
With time, genetic changes built up within
each
population – became separate species!
Prefer moist-low lying areas
Prefer higher drier areasSlide17
3) Temporal Isolation
2 populations may share an ecosystem.
BUT
reproduce
at a
different time of year.
Ex:
Plants – blooming different times of the day.
Animals – different mating seasons (spring and fall).
Prefer Spring
Prefer Fall
Two species of termites are REPRODUCTIVELY ISOLATED because they are
not mating at the same time of the year.Slide18
4) Behavioral Isolation
Even if 2 populations/species occur in the same place and same time, they may still be isolated by BAHEVIOR.
Animals have characteristic behaviors that allow males and females to recognize each other and trigger mating.
Enough difference between populations – NO mating.
Ex: firefly.
Emitting specific patterns of flashes to attract females.
Female not recognizing pattern of
flashes (from
different species)
.
No matingSlide19
Another example: crickets
Emit characteristic chirps to attract females
Female recognizing it
Mating happens
Female NOT recognizing chirp pattern
No Mating
Pattern of chirps is UNIQUE to each species.
This helps prevent mating between different members of 2 different species (i.e. PREVENTS
INTERBREEDING
).
Other examples of behavioral barriers to reproduction: bird songs, chemicals given off by insects.Slide20
5) Mechanical Isolation
When animal or plant reproductive structures are NOT compatible.
Result: Mating CAN’T occur.
Ex: Dragonfly
Male dragonfly has claspers for holding on to female during mating.
If
male grabs female of wrong species, he will be in wrong position, and sperm transfer won’t
occur.
Genitals
– like lock and key (one key for the lock).
So those dragonflies can only SUCCESSFULLY mate with member of their own species.Slide21
6) Gametic
Isolation
Even if gametes (sperm and egg) meet, they may not form a viable zygote.
Ex:
Sperm of one animal species can’t survive in the reproductive tract of another species.
Egg may have chemical barriers that prevent sperm of another species from entering it.Slide22
Post-zygotic Isolating Mechanisms
Sometimes individuals mistakenly mate with a member of the wrong species and transfer gametes.
BUT
there are STILL mechanisms to prevent
interbreeding
Post-zygotic
isolating mechanisms.Slide23
When?
h
appen at or after a zygote is being formed.
How?
t
hey prevent hybrid offspring from developing OR being able to breed later.
Worst case
:
E
ven if Zygote forms and develops into an adult, barriers still occur to prevent interbreeding.
Hybrid could be sterile (can’t reproduce) or
H
ybrid’s offspring (F2 generation) can have high mortality (death) rate.
interbreeding
Hybrid produced.
Sterile (can’t reproduce when mating)
F2 generation
DIEDSlide24
Post-zygotic mechanisms:
Zygote mortality
Several species interbreed but when they mate, the zygote fails to develop (ex several species of frog).
Hybrid offspring are sterile
Donkey interbreeds with a horse, offspring is a mule.
Mule can’t reproduce.
Genetics of the two species then don’t PERMANATENTLY mix.
If hybrid offspring (F2 generation) are not sterile,
They still may be less fit than their purebred competitors.Slide25
Reproductive Isolating Mechanisms - SummarySlide26
Support Questions
21, 22, 23Slide27
CONTENT SUMMRY
:
Species & Speciation.
Reproductive isolating mechanisms
Pre-zygotic.
Post-zygotic.
Examples of Speciation.
Grasses.
Darwin’s Finches.
Polyploidy in Plants.
Hybrids.
Types of Selection
Stabilizing.
Disruptive.Directional
Human Impact on Evolution – Polar Bears, Climate Change, & Hybrids.Slide28
Examples of Speciation
It occurs when
enough genetic differences
build up between two populations
That they
can no longer interbreed successfully
.
Easiest way – two populations physically
seperated
.
Question:
What about if two populations were in the same place at the same time. Would speciation occur? How?Slide29
Ex 1 - Grasses
Stage 1 – Geographic IsolationSlide30
Stage 2: Reproductive Isolation (barrier to gene flow)
Oil Spill
Evolving higher frequency of genes tolerant to oil
OIL TOLERANT PART
Can interbreed but diverged genetically so hybrid offspring are not successfulSlide31
Darwin’s Finches
Speciation happens faster in small than large populations.
Galapagos finches became geographically isolated n their separate islands.
Developed different genetic makeups.
Evolved to different selection pressures on their islands.
Long beak
Eating insects in rocks
Short beak
Eating seeds and fruit.
Genetic differences became so great
Result: when brought together, unable to reproduce successfully.Slide32
Polyploidy in Plant
Random mutations in some plants – chromosome number doubles in gametes.
Polyploid
gametes
normal gametes
Polyploid
gametes
Polyploid
gametes
Fertilization - NO
Fertilization - Yes
Fertile offspring with double chromosomes.
Polyploidy individuals are reproductively isolated from the rest. If enough is produced, they can create their own breeding alongside the normal plants.
First step to creating a new species (accomplished even by genetic barrier rather than physical one).Slide33
Hybrids
Speciation can happen through hybrids.
HOW?
If two species interbreed and create a sterile hybrid, the hybrid can still reproduce
ASEXUALLY
(ex: sending up shoots or cloning/copying).
If produce enough copies, they create a small breeding population.
Reproductively isolated from parents but
can breed amongst themselves.
Gradually, sterile hybrids can change into fertile polyploids (remember mutation, drift, and selection as ways of changing allele frequency) and a new species can form.
CloningSlide34Slide35
Support Questions
24Slide36
CONTENT SUMMRY
:
Species & Speciation.
Reproductive isolating mechanisms
Pre-zygotic.
Post-zygotic.
Examples of Speciation.
Grasses.
Darwin’s Finches.
Polyploidy in Plants.
Hybrids.
Types of Selection
Stabilitizing
.Disruptive.
DirectionalHuman Impact on Evolution – Polar Bears, Climate Change, & Hybrids.Slide37
Types of Selection
Genetic differences between populations build up to the point where they become different species.
How does genetic divergence happen?
Natural selection creates either a divergence (i.e. separating) or convergence (
i.e
coming together) of traits,
leading to a change in the population and perhaps eventually speciation.Slide38
In natural population, traits are usually distributed in a normal bell-shaped curve.
Most individuals are close to the average for the trait (peak).
Few are either very low or high (lower & upper tails of curve).
Ex: Height (most are average, few shorter, few, very few extremely short and very few extremely tall).
Height shows some variation which natural selection can act upon.Slide39
How does selection relate?
Selection changes the shape of the bell curve for traits over time.
3 kinds of selection: stabilizing, disruptive, and directional.Slide40
1) Stabilizing Selection
When selection favors middle values of a trait + is against the two extreme values.
Ex: height in plants and birth weight of babies.
Tall plants (Affected by wind)
Short plants (Sunlight can’t reach)
Medium size plantsSlide41
What do selection pressures do in this case
?
Lower the fitness of short or tall plants.
Reward plants of medium height.
Result:
N
umber of medium height plants increase
Number of tall and short plants decreaseResult on bell curve: narrowing it.Slide42
2) Disruptive Selection
Selective pressures act
againts
individuals possessing the average trait.
Result: bimodal/two-peaked curve
The two extremes of the curve create their own smaller curves.Slide43
Ex: plants with variation in height + pollinated by three different bee species.
Tall plants (Affected by wind)
Medium size plants
Short plants (Sunlight can’t reach)
Attracted to
Attracted to
Attracted toSlide44
This bee species disappeared
So won’t be able to reproduce
Population would tend toward both short and tall, but not medium-height plants.
Divergence in the population & reproductive isolating mechanism (short and tall can’t exchange pollen).
Eventually the two populations could diverge enough on other traits – leading to speciation.Slide45
Another example – Darwin’s finches
Plants produce either large or small seeds.
Bird population start with medium-sized beak would not be as efficient at gathering seeds.
Birds with slightly smaller beaks – better eating smaller seeds.
Birds with larger than average beaks – better eating larger seeds.
Birds with medium beak – nor efficient at gathering either.
Over many generations, two beak sizes are selected (small and large), and birds with medium-sized beaks die out.
Large beaks
Medium beaks
Small beaksSlide46
Directional Selection
Individuals that are either above or below the average do better, depending on where natural selection was pushing them.
Result: over time, population’s trait distribution shifts towards the favored type.
Mean/average of the population graph shifts to the left/right.
Ex: Giraffe necks.Slide47
Selected against
(couldn’t reach as many leaves to feed)
So:
distribution of neck lengths shifted
to favor those with long necks.
Leading to higher percentage of giraffes having long necks, eventually
dominating (taking over) the gene pool
Today – only long-necked giraffes are present
.Slide48
Another example - horses
Early horses – small and slow runners (adapted to forest environment).
Modern horse – large and fast (adapted to life on grasslands).
WHY?
E
nvironment changed - forests replaced by grasslands.
SO larger individuals did better because they had strength and speed to outrun predators.
With generations, average size of horses in the population increased (so shifting the bell curve average).Slide49
Support Questions
25Slide50
CONTENT SUMMRY
:
Species & Speciation.
Reproductive isolating mechanisms
Pre-zygotic.
Post-zygotic.
Examples of Speciation.
Grasses.
Darwin’s Finches.
Polyploidy in Plants.
Hybrids.
Types of Selection
Stabilizing.
Disruptive.
DirectionalHuman Impact on Evolution – Polar Bears, Climate Change, & Hybrids.Slide51
Human Impact on Evolution – Polar Bears
Considered at risk of being endangered due to global warming.
Eat seals and small whales as they hunt out on the frozen Arctic Ocean.
If ice melts, bears can’t hunt
for
seals
and they will starve.
Arctic ice pack has remained stable but that is rapidly
changng
.Slide52
Impact of Global Climate Change
Earth’s climate – rapidly changing (humans burning fossil fuels, releasing carbon dioxide and greenhouse gases into atmosphere).
Gases trap heat against Earth’s surface –
gradual warming
.
Earth slowly warms up –
effects dramatically felt in polar areas
.
Arctic Sea forms later
every fall
and melt earlier
every spring.
Amount of Ice shrinks + longer ice-free periods every year,
polar bears are forced onto shore earlier. So they slowly starve until ice forms again.
Bears are dying younger + fewer offspring produced as ice gradually disappears.Grizzly beards are brought into polar bear territory
since the Arctic, as it warms up, is becoming a more favorable habitat for grizzly bears.Slide53
Hybridizatio
n
Grizzly bears and polar bears – close relatives.
Two species kept separated by isolation in different habitats.
Polar bear – lives on ice and feeds on seals.
Grizzly bear – lives on land and feeds on vegetation and prey
.
Example of Reproductive isolation (
georgraphic
& behavioral mechanisms).
Today, climate change changed bear habitats and movements throughout the Arctic.
Taking grizzly beards into habitats brining them in direct contact with polar bears.Slide54
Hybridization two concerns:
Aggressive Grizzly bear outcompeting or attacking the polar bears.
Grizzly and polar bears interbreed, forming hybrids.
Could lead to less fit individuals not well adapted to life on the land or ice.
Why know this? Because human-caused climate change can be leading to new directions in evolution for the polar bear.Slide55
Support Questions
26 & 27Slide56
CONTENT SUMMRY
:
Species & Speciation.
Reproductive isolating mechanisms
Pre-zygotic.
Post-zygotic.
Examples of Speciation.
Grasses.
Darwin’s Finches.
Polyploidy in Plants.
Hybrids.
Types of Selection
Stabilizing.
Disruptive.
DirectionalHuman Impact on Evolution – Polar Bears, Climate Change, & Hybrids.Slide57
Key Questions
12 to 15.
Unit End.