Transcript Processes of Evolutionx

Patterns of Evolution
External 3 Credits
Do Now
• Define the following terms;
•
•
•
•
Population
Species
Gene pool
Natural Selection
Answers
• Population; is a group of individuals of the same species in an
area.
• Species; is a groups of individuals who normally interbreed to
produce fertile offspring and who belong to the same gene
pool.
• Gene pool; all the alleles available to the population of a
species.
• Natural Selection; the process were the organsims with the
best suited phenotype in a particular environment is select for
(has increased survival)
Lesson Objectives
• Review Yr 12 Evolution
A new idea?
The idea that life has
evolved is not new and
goes back to the
civilisations of the
ancient Greeks.
Christianity has a different
perspective and is
detailed in various
passages in Genesis in
the bible.
EVOLUTION
• Macro-Evolution
 Large changes in a gene pool over a long
period of time, as in the formation of a
new species, extiction and adaptive
radiation
• Micro-Evolution
 Small changes in the frequency of alleles in
a gene pool over successive generations
Who evolves?
Write this
down!!!
• Individuals do not evolve – only populations
evolve.
• All the genes in a population are called a gene pool - the
ratio of alleles and genotypes in a population can change
over time.
• As this changes, so evolution occurs.
Sources of Variation
1. Meiosis (covered in Yr 12)
2. Mutations
Processes of Evolution
1. Genetic Drift
2. Founder Effect
3. Bottleneck Effect
4. Gene migration
5. Natural Selection
Meiosis
• Independent Assortment
• Segregation
• Crossing over
What is a gene pool?
Remember!! All the
alleles present at
all gene loci in
all members
of a population
GENE FLOW (results from Migration)
 Individuals migrate between populations.
 Immigrating individuals introduce new
alleles.
 Emigrating individuals remove alleles.
• Gene flow can change a gene pool due to the movement of
genes into or out of a population
Mutation changes alleles
► Natural selection leads to differential reproductive success
►
Genetic Drift
• A change in the gene pool of a small population due to chance
 Genetic Bottleneck
 Founder Effect
There are several potential causes
of microevolution
• Genetic drift is a
change in a gene
pool due to chance
• Genetic drift can
cause the bottleneck
effect
Original
population
Bottlenecking
event
Surviving
population
Figure 13.11A
• Population bottleneck
– genetic drift due to
high mortality in a
population.
• Unlikely that gene pool of the
remaining population is
representative of original
population.
Decreased genetic diversity
among Cheetahs.
Cheetahs underwent 2 population
bottlenecks:
1st during last ice age
2nd during nineteenth century due to
excessive hunting.
Today, just two isolated populations live in
South & East Africa, numbering only in a few
thousand animals between them. The South
African cheetahs are so genetically alike that
even unrelated animals can accept skin
grafts from each other.
• or the founder effect
Figure 13.11B, C
Founder effect
genetic drift
• Equivalent to
due to a few individuals
leaving a large population to found a new group.
 Unlikely that gene pool of founding population is representative
of original population.
Founder effect
Direction of movement
Mainland Population
Island Population
28 61%
4 44%
12 26%
5 56%
6 13%
Founder effect
• Thus isolated populations of a species may have very different
genes from the parent population and would therefore have a
different susceptibility to the effects of natural selection on
them at these new localities.
The Laysan Finch Story
• Small population on Laysan Island and
of conservation concern.
• A group of 10 males and 10 females
were captured and transported to a
similar island 500 nm away.
• They were individually marked and
samples of their DNA were taken prior
to release.
• The introduced population thrived and
samples of their DNA taken 5 years later
showed a greater variation than the
initial population.
• How come?
Laysan Island
5 genes go with the original
population.
500 nm
New Island
2 new genes appear, giving a
new total of 7 genes in the ‘new’
population.
Non-random Mating
 Non-random mating causes certain alleles to become
more common in future generations (some
individuals leave more offspring than others).
Gene migration (Gene Flow)
• Most populations are
not closed systems.
• Immigration from
other populations
brings in new gene
combinations.
• Those individuals, who
leave the population
(emigrate), take their
genetic combinations
with them.
• I=in e=exit
Mutation
• A change in the DNA - introduces ‘new’
alleles into the population. Mutations can
be beneficial, have no effect (silent) or be
harmful.
Increase or decrease of genetic
diversity???
• Mutations and immigration increase genetic diversity.
• Natural selection, emigration, non-random mating and genetic
drift decrease genetic diversity.
Important Slide!!!!
Write this down!!!!!
Natural Selection
Write this
Down!!
 The differential survival and reproductive success of
organisms whose genetic traits- PHENOTYPES increase
their chance to survive and reproduce in a particular
environment.
 It is considered to be the major driving force of evolution.
Natural Selection Summary
Over-production of young
Competition
Genetic Variation (ie different phenotypes)
Differential Fitness (Reproductive Success)
Fittest outcompete others to pass their “fit/favourable” genes onto
their offspring
• These “favourable” genes will then increase in frequency
•
•
•
•
•
Speciation
• Speciation is the formation of a new species
• Remember: A species is a group of organisms that normally
interbreed in nature to produce fertile offspring & belong to
the same gene pool
• There are 2 types of speciation:
 Allopatric Speciation
 Sympatric Speciation
Allopatric speciation
• Species can be allopatric – living in geographically
different areas.
Species B
Species A
Sympatric species
• Species can by sympatric – living together in the same
geographical area.
Species A & B live in all areas in the same geographical area.
The mechanism of speciation
Allopatric speciation
This is how most species come about.
A single population occupying a uniform environment
Species undergoes an expansion of range
Migration into new environments on the edge of the distribution
Gives rise to subspecies as a result of different selection pressures.
There is gene flow between all populations still.
Vegetation change
Selection the same
River course change
Selection the same
Further migration, environmental differences and the
development of geographical barriers, gives rise to
geographical isolation of some races and populations.
This isolation halts gene flow between this and
the original population.
Selection the same
Selection different
Different alleles being
selected for.
Some of the isolated populations develop genetic and
chromosomal differences that no longer allow inter-breeding
with the parent population. The subspecies is genetically
and geographically isolated from its ancestral population.
Further changes in the environment remove the geographical
barrier and allow the groups to live side by side. There is no
interbreeding because some of the groups are now
reproductively isolated, due to the different selection pressures
they have been exposed to.
Gene flow can occur between
these populations still as they
have been exposed to the same
selection pressures.
There is NO gene flow between
these populations now,
because of different selection
pressures resulting in
Genetic changes.
These now become
Sympatric
and
Allopatric populations
Allopatric Speciation – an
example
The mechanism of speciation
Sympatric speciation
There are very few authenticated reports of speciation by this route.
If it does occur, it happens within one generation.
Starting with one
population
A very small portion of the population undergoes a
random mutation, which gives them instantaneous
reproductive isolation from the rest of the species. It
has to occur in a male and female in the same
generation and must confer an immediate
evolutionary advantage and separation from the
parent population.
Polyploidy
• This is the abrupt and almost instantaneous formation of a
new species.
• The main cause of this is a problem of separation of the
chromosomes at Meiosis into the gametes and we will deal
with it later on.
• Rare in vertebrates but common in plants.
Aims for Today
• To be able to explain the pre-zygotic and post-zygotic isolating
mechanisms that lead to speciation.
Formation of species
• Prevention of gene flow between populations can result in the
formation of new species.
• These are called isolating mechanisms.
• There are pre and post-zygotic isolating mechanisms.
How does it happen?
• Pre-zygotic isolating mechanisms prevent the fusion of
gametes to form a zygote.
• Post-zygotic isolating mechanisms prevent the zygote from
developing further, if fertilization occurs.
Pre-zygotic mechanisms
Geographical barriers
• Populations are
geographically isolated.
• Scale is important.
Pre-zygotic mechanisms
Ecological barriers
• Live in different areas
with different
temperatures, humidity,
altitude tolerances etc.
e.g. Arctic Fox and Fennec
Fox
Pre-zygotic mechanisms
1.
2.
3.
4.
5.
Habitat differences.
Breeding season differences.
Behavioural differences; territoriality & courtship and the context of
the displays.
Mechanical differences.
Mating takes place but no zygote formed (duck sperm does not
survive reproductive tract of a hen)
Post-mating mechanisms
1.
2.
3.
Hybrid inviability – zygote formed but it does not
develop.
Hybrid sterility – hybrid forms but it is sterile – mule.
Hybrid breakdown – hybrid is fertile but offspring
cannot reproduce.
A lion x tiger hybrid
Weighs 450 kg and is 3 m
From nose to tail.
We’ve talked about mules
What about a zeedonk?
Isolation by time
A species, which has gone extinct, can obviously
not interbreed with a species existent today.
Isolating
Mechanisms –
an overview
Speciation
• The formation of a new species - speciation and can occur in
the following ways:
• Reduced selection pressure – a population moves into a new
area, where the selection pressures are different.
• An increase in population results in the expression of alleles,
which were previously selected against.
More speciation
• Migration into new areas, which might have different selection
pressures.
• Some isolated populations develop genetic and chromosomal
differences that no longer allow interbreeding with the parent
population.
Formation of species
• Prevention of gene flow between populations can result
in the formation of new species.
• There are two main schools of thought as to
how this is achieved.
Time
Phyletic gradualism – genetic change takes place gradually
over a long time.
Amount of difference
Punctuated equilibrium – rapid genetic change followed by long periods of
stability.
Time
Extinction
Amount of difference
Patterns of Evolution
• Sequential Evolution; species may accumulate genetic changes that,
over time, result in the emergence of what can be recongised as a
different species.
• Coevolution; where two species reciprocally affect each other’s
evolution.
• Convergent Evolution; Species from different evolutionary branches
may come to resemble each other if they have similar ecological
roles and natural selection has shaped similar adaptations.
• Divergent Evolution; the process where two species have diverged
from one common ancestor. (most common form of evolution)
Convergent evolution
• Species from different evolutionary branches may come to
resemble each other if they have similar ecological roles and
natural selection has shaped similar adaptations.
Convergent evolution
• Homologous-descended by inheritance from a common
ancestor e.g. the pentadactyl limbs shown in the diagram
Convergent Evolution
• Analogous structures; similar function and often the same
superficial structure, but of different evolutionary origins
• E.g the wing of a bird and the wing of an insect.
Co-evolution
Co-evolution
• Co-evolution is used to describe cases where two or more
species reciprocally effect each other’s evolution.
• Each of the species involved exerts selective pressures on the
other and over time the species develop a relationship that
involves mutual dependency.
• Co-evolution is likely to occur when species have close
ecological interactions with one another.
New Zealand’s pollinators
• When New Zealand split away from Gondwana its insects did
not include types of bees or any other insects that are
attracted to bright colours.
• So….. Insects and plant needed to evolve adaptations that
enabled the insects/birds present to obtain food from the
plant while at the same time carrying pollen from flower to
flower.
Coevolution
• As a result insect pollinated flowers in New Zealand flowers
become dull in colours with strong nectar scents. This
attracted small beetles, butterflies, moths and small bats.
• Several of the birds of the forest developed adaptations such
as long, feathers tongues for feeding on nectar. At the same
time some forest trees adapted to attract birds by evolving
bright colour and nectar production. E.g Kowhai and tui’s
Adaptive radiation
• Adaptive radiation is the diversification (both structural and
ecological) among descendants of a single ancestral group to
occupy different niches.
• In adaptive radiation is a pattern of evolution that involves an
ancestral species evolving into a variety of new species, each
adapted to survive in a different niche.
Adaptive Radiation
EXAMPLE: The radiation of the mammals occurred
after the extinction of the dinosaurs, which has made
niches available for exploitation.
Arboreal herbivore
niche
Marine predator
niche
Terrestrial
predator niche
Underground
herbivore niche
Freshwater
predator niche
Flying predator/
frugivore niche
Browsing/
grazing niche
Megazostrodon
an early mammal ancestor
Divergence and Radiation
of the Ratites
Mesozoic Era
Cenozoic Era
All other living
birds
Birds evolved from a
dinosaur ancestor about
150 million years ago
Moa 1: Anomalopteryx
Moa 2: Pachyornis
Moa 3: Dinornis
Moa 4: Megalapteryx
Little Spotted Kiwi
Great Spotted Kiwi
Fossil evidence suggests
that ratite ancestors
possessed a keeled
breastbone and an archaic
palate (roof of mouth)
Ratites diverge from
the line to the rest of
the birds about 100
million years ago
Brown Kiwi
Emu
Cassowary
Ostrich
Elephantbird
Rhea 1
Rhea 2
Tinamou (can fly)
6 important events
1.
2.
3.
4.
5.
Isolation
Mountains
Sea level changes
Climate change
North and South extent
Isolation
• Isolation is a key reason why the endemic species of New
Zealand are so different.
• 300 million years ago New Zealand was part of
Gondwanaland. Gondwanaland was made up of Africa, South
America, Antarctica, India and Australia
• Initially New Zealand was under the sea and was attached to
the eastern side of Australia
• 70 to 80 million years ago, New Zealand was pushed away
from the Australia
Isolation
Isolation
• When New Zealand sperated from gondwanaland only the
plants and animals present at the time of sepration could
become the ancestors of the present species
• As a result New Zealand only had a small range of kinds of
plants and animals
• These species eveloved in isolation for many millions of years
Mountian Building
• 24 million years ago New Zealand was sitting on tectonic plate
boundary.
• Pressure within the earth caused uplift into large mountians
• This created a new alpine habitat for things already living
there
• It also caused isolation which seprated different parts of the
country and weather patterns such as wetland on the west
coast of the south island and the dry plains in Canterbury and
Otago
Climate Changes
• Mountian building and ice ages contributed to dramatic
changes in New Zealand’s climate
• 20,000 year ago most fo New Zealand was covered in snow
fields, this caused
• Some plant species to move north e.g nikau tree
• Some plants to become extinct e.g. eucalypts
• Some plants to evolve to better suit the conditions.
Changing Sea levels
• At times changes in the sea level isolated or joined different
parts of the country
• As recently as 12,000 years ago the cook strait was dry land
and island such as great barrier were part of the main land of
New Zealand
• As the last ice age finished the sea level rose and separated
the north and south island
North to South Extent
• New Zealand is long and narrow, with varying climates all the
way along it.
• This enabled tropical species to evolve in the north and alpine
species to evolve in the south.
New Zealand Hebe
• There are more than 80 species of Hebe in New Zealand.
• Most species are restricted by their adaptations to very
specific areas.
• The original New Zealand Hebe was probably a shrub with
normal-sized leaves in an alternate pattern with pale flowers.
• Today there are three main groups of hebes.
Large –Leafed hebe
• Large hebes are most like the ancestrial hebe.
• Leaves are untoothed and either broad or narrow but never
overlap.
• Flowers are pale and larger than the leaves
• Found in lowland shrub, on the coast, in forest margins
• NOT FOUND IN EXTREME ENVIRONMENTS
Medium-leafed hebes
• Have features that would help the plant to withstand dry, arid
conditions with wind and cold.
• Toothed, fleshy leaves
• Leaves are flat and concave and are short and closely
set……………………
• Flowers are spikes crowded together
• Found in sub-alpine regions, mainly on rocks
Small-leafed hebes
• Have adaptations to withstand cold and snow and are able to
survive the harsh conditions of bare rock
• Plants are small and spreading………..
• Leaves are very small, overlapping and tough…………..
• Flowers have only a few spikes, crowed near the tips of the
branches.