Biology 3.5
Patterns of Evolution
Credits: 4
External
! Before we begin…
From the examination specifications…
Giraffe Evolution?
Revision
12 bio stuff…
Stuff u should know from Year 12
• Natural Selection
– Directional
– Disruptive
– Stabilising
•
•
•
•
•
•
•
Founder effect
Population bottlenecks
Genetic drift
Mutation
Gene flow
Migration
Factors affecting allele frequencies…
Darwin vs Lamarck
Natural Selection in a NutSHELL
Variation
Individuals vary in
phenotype (physical
traits). Some variants are
better suited to the
current environmental
conditions. The better
suited survive better and
leave more offspring.
Natural Selection
The alleles of the better
suited increase in the
population, they are said
to be ‘selected for’.
Inheritance
Variations are passed on to
offspring. If the selection
pressure is maintained each
new generation contains
proportionally more
descendants from
individuals with favourable
characteristics than those
with unfavourable.
Some variation is lost.
Natural Selection
Requires:
Variation
Selective Pressure
Inheritance
Result:
Selection of the
‘fittest’ variants and
their genes.
Bio 3.5
Level 3 from here
The “Species” Concept
“a group of actually or potentially interbreeding natural populations that is
reproductively isolated from other such groups”
Main Problem:
- Closely related species produce fertile offspring eg Canis spp.
- Genetically isolated species may be morphologically similar = cryptic species
(morph = “body”)
Main Solution:
- Use DNA analysis to clarify relationships between closely related species.
- BUT: how much difference = different species, subspecies….??
Extinct: 10,000 years bp
Clines & Ring Species
• Cline: A gradation in one or
more characteristics within a
species esp. between different
populations.
• Ring Species: A series of
neighbouring populations that
can interbreed, but for which
there exist at least two "end"
populations in the series that
are too distantly related to
interbreed
In this diagram, interbreeding
populations are represented by
coloured blocks.
Variation along a cline may bend
right around, forming a ring.
Larus (gull) ring species
No, gull away!
Are you my type?
A Herring Gull, Larus argentatus
(front) and a Lesser Black-backed
Gull. Larus fuscus (behind)
The Larus gulls interbreed in a ring around the arctic
(1 : Larus argentatus argentatus, 2: Larus fuscus sensu stricto, 3 : Larus fuscus heuglini, 4 : Larus
argentatus birulai, 5 : Larus argentatus vegae, 6 : Larus argentatus smithsonianus, 7 : Larus
argentatus argenteus
Neighbouring groups can hybridise (breed together) but sufficient differences exist to prevent
groups 1 & 7 breeding.
Californian Salamander Ring Species
The many subspecies of
Ensatina salamanders in
California exhibit subtle
morphological and genetic
differences all along their
range. They all interbreed with
their immediate neighbours
with one exception: where the
extreme ends of the range
overlap in Southern California,
E. klauberi and E. eschscholtzii
do not interbreed.
So where do we mark the point
of speciation?
Stages in Species Development #1
• Species rarely explode suddenly into existence (species
formation is usually slow)
• General pattern:
– Homogenous population splits (cause = geographical barrier)
– Different natural selection pressures, mutations  gene
frequencies change
– Races form as gene flow reduces, factors preventing mating
begin (“prezygotic”)
– Gene flow further reduces, post zygotic factors occur (hybrid
sterility – eg as in mule)
– Now = two different species.
Variation in Human Skin Colour
Stages in Species Development #2
- A generally predictable series of events occurs as a
homogenous ancestral population evolves into two
separate species.
- The key to this is build up of genetic differences as a
population is split into two populations. Barriers to
frequent mating mean that differing natural selection
pressures and mutations are not shared  populations
go down different genetic pathways.
- Eventually differences build to where the populations
become separate races.
- With enough differences races become difference
subspecies, then separate species.
Extinction Extinction
Sumatran tiger
Sumatran tiger: http://en.wikipedia.org/wiki/Sumatran_tiger
Sumatran tiger clip: http://www.theawl.com/2011/05/get-a-good-look-at-these-awesome-tigers-theyre-almost-extinct
Call of Life (extinction video trailer): http://www.calloflife.org/p-trailer.htm
Extinction
• A natural process – all species that have evolved will eventually go extinct
• Duration of persistence of a species varies (often from 1 million years for
complex organisms to 10-12 million years for simple organisms)
• Extinction and mass extinction provides opportunities for other organisms to
evolve and fill vacant ecological niches.
Humans: How long have we been around? When will we become extinct?
• Anatomical modernity: 200,000 years ago
• Behavioural modernity: 50,000 years ago
• Future…”currently using resources at rate of 8 planets worth”
“Fred” a preserved dodo,
Raphus cucullatus
Haasts Eagle & moa
Huia
Coelacanth
Latimeria chalumnae (60kg, 170cm long)
Coelacanths were thought to have gone extinct in the Late
Cretaceous (~65mya), but were rediscovered in 1938 off the coast of
South Africa. 2 Known extant species. The coelacanth has been
nicknamed a “living fossil”, because its fossils were found long before
the actual discovery of a live specimen. The coelacanth is thought to
have first evolved approximately 400 million years ago.
Processes of Evolution
The Role of Mutation
• Notes + BZ
• 90,92-98
The Role of Gene Flow
• Notes + BZ
• BLB 158-160
Oligocene Drowning
• http://www.odt.co.nz/lifestyle/magazine/251
158/theory-flounders
• http://www.stuff.co.nz/environment/215430/
NZ-was-never-underwater-scientists
Kiwi an Australian?
• http://www.nzherald.co.nz/nz/news/article.cf
m?c_id=1&objectid=11259906
• http://www.adelaide.edu.au/news/news7068
2.html
Speciation
• “Process by which one species gives rise to two or
more new species”
• Multiplication of spp. not gradual change over time
Allopatric Speciation
Usually:
• Pops get geographically separated (eg by river)
• Gene flow reduces, Genetic isolation occurs.
• Diffs in natural selection can cause diffs in allele frequencies
between the pops over time. AND: mutations occurring in one
population will not be transferred by migration to other
populations (no gene flow)
• Diffs accumulate, when the pops are reunited they may now no
longer interbreed = separate spp.
• NZs isolation/islands has led to many egs of allopatric speciation.
(changing sea levels, mountain building, ice ages have also had an
impact)
Allopatric Speciation
Allopatric Speciation: Snapping Shrimp Example
15 different species of shrimp on EACH side of the
Isthmus of Panama (3mya). How could this occur?
In a single population of shrimp (before the
isthmus), a mutation that arose in one
individual could eventually spread through the
whole population as the shrimp mated with
each other. But once there is a barrier splitting
the population in half, a new mutation can
only spread through half the population. That
is why a lack of interbreeding means the two
populations evolve separately.
There can also be slightly different factors for
survival in the different areas: maybe the
temperature or currents are different on each
side; maybe the food sources are different.
This can also help the populations diverge, or
become different, from each other.
Reptiles again…
Allopatric Speciation Questions
1. Why have many NZ birds lost the ability to fly (cf to their
Aussie relatives)?
2. Glaciation creates many isolated mountaintops – how would
this contribute to allopatric speciation?
3. How could sea level rise/fall create new species through
allopatric speciation?
4. Describe how an ancestral robin species gave rise to the
Chatham Island robin and the mainland robin.
5. Describe ALL potential geographical barriers (read the sheet
“geographical barriers”
6. Explain how one NZ plant and one NZ animal came about as
a result of allopatric speciation (read the sheet “allopatric
speciation in NZ animals and plants”
Sympatric Speciation
• ‘speciation NOT involving a period of
geographic separation”
• Much rarer than allopatric speciation
• More common in plants
• Rest of notes on OHT (sigh)
Nonallopatric Speciation occurs with
no evidence of physical barriers
Geography is not the only way a
population can separate
The huge variety of cichlid fishes in
African lakes are found nowhere else;
yet the lakes are evolutionarily young
and without barriers.
Individuals can speciate while living in
different components of the
environment. African cichlid fishes show
very different feeding specializations
Polyploidy
Non-disjunction
• BZ figs pg 114
• Animation
• Inc polyploid def
This image shows haploid (single), diploid
(double), triploid (triple), and tetraploid
(quadruple) sets of chromosomes. Triploid and
tetraploid chromosomes are examples of
polyploidy.
Inducing Non-Disjunction
• Done deliberately to create new plant varieties
• Often larger, more vigorous than parents
• Uses seeds/seedlings soaked in colchicine / N2O*
gas
– Inhibits spindle fibre formation
– Chromosomes fail to separate
– Resulting gametes may lead to polyploid plants
• Propagated asexually or crossed if fertile
*yes that is nos, nitrous oxide….
Polyploidy as a Source of Variation #1
• Background
• Allo & auto
• Hybrid vigour…
Polyploidy in Manuka
Don’t get confused
•
•
•
•
•
Polyploidy
Polysomy
Anueploidy?
Allopolyploidy
Autopolyploidy
Teosinte  Modern Corn (~1000yrs)
Wheat
Spelt
• Where does this fit in wheat
development?
• Hybrid of emmer wheat
• & goat grass in near east before the
hexaploid bread wheat appears
• See footnotes for more…
• Nb bread wheat 8000 years ago
•
http://en.wikipedia.org/wiki/Spelt
Reproductive Isolating Mechanisms
• Notes uploaded to weebly…
Lacewing Songs:
• http://www.pbs.org/wgbh/evolution/library/0
5/2/swf_pop/l_052_01.html
Evolutionary Relationships - Terms
• Phylogenetics: the study of evolutionary relatedness between
groups of organisms. Relatedness is determined by DNA
sequencing data and comparing morphological data
• Phylogeny: The evolutionary development and history of a
species or higher taxonomic grouping of organisms.
• Cladogram: Diagram which shows ancestral relations
between organisms
• Cladistics: method of classifying species of organisms into
groups called clades, which consist of an ancestor organism
and all its descendants (and nothing else).
Cladograms
• Show ancestral relations between taxa
– Using DNA analysis or morphological comparisons
• Species are at the “leaves”
• Common ancestor at the “trunk”
• Have an implicit time axis (runs forward from base to leaves) but:
problems of scale, data quantity & quality
• May show extinct species, but: DNA from extinct species is rare
canids are an old lineage, separating from the
Simplified Canid Phylogeny *The
other carnivores about 60 million years ago.
of a "wolf" branch, a "South American"
(shown in the cladogram below)Separation
branch, and a "red fox" branch occurred more
time
recently, 7-10 million years ago.
a clade
*Mitochondrial DNA analysis of both modern and
historical specimens of red wolves failed to
distinguish red them as a species separate from gray
wolves or coyotes. They appear to be a hybrid
species, and can interbreed with either gray wolves
or coyotes.
*Two different dates for the origin of dogs have
been suggested. Mitochondrial DNA analysis
suggests a date between 60-100,000 years ago -well before the beginning of human agriculture.
Other genetic and archeological evidence suggests a
more recent date -- about 15,000 years ago.
Neolithic cave drawings also show dogs hunting
with humans.
common ancestor
species
*All domestic dogs are the descendants of a few
ancestral wolf stocks originating in Asia. Surprisingly
this includes New World dogs, who were once
thought to have been independently domesticated
from New World wolves.
Molecular Phylogeny (DNA analysis) may revise
past phylogenies (based on morphology)…
The Squamata, or the scaled reptiles, are the
largest recent order of reptiles, comprising all
lizards and snakes.
Hedges, S. Blair, and Poling, Laura L. A Molecular
Phylogeny of Reptiles. Science, Vol. 283,
No.5404, pp.998-1001
• The study also cast in doubt the relationship
between the tuatara and squamates. While
fewer gene sequences were available for the
tuatara, six of eight comparisons showed
closer affinities with archosaurs or turtles,
while only two showed squamates as the
closest relative. While the results of this
study are not conclusive, it clearly
demonstrates that we don't know all that we
thought we knew about the phylogenetic
relationships of living or fossil reptiles.
http://home.pcisys.net/~dlblanc/articles/TurtleP
hylogeny.php
Convergent Evolution
• The evolution of the same biological trait in unrelated groups / species.
• Examples:
– Shark, icthyosaur, dolphin, penguin (a fish, reptile, mammal and bird
respectively) are unrelated but have evolved a similar streamlined shape and
“fins” in response to their environment (water) which provides a common
selection pressure (in this case fast movement through water)
– Unrelated plants have evolved water storage tissue (succulent tissues) eg
Euphorbia, cacti in response to their environment (dry desert) which provides a
common selection pressure (need to store water during prolonged dryness)
• Analogous structures “structures that are alike in function but have a
different evolutionary origin”
– Egs: wings of insects and birds; mammalian and octopus eye
Human eye vs Octopus eye
Unrelated organisms (vertebrate vs mollusc)
Developed similar eye as a result of selection
pressure for well developed sight (see prey clearly,
3D)
The eye is an analogous structure
Dolphin
Icthyosaur (2-4m)
Penguin
Shark
Convergence in Plants
Ferocactus pilosus (Mexican lime cactus)
These unrelated plants have separately evolved the ability to store water in
their stems.
This is a response to the natural selection pressure of dryness in the desert.
The swollen stems are an example of an analogous structure
Example (reading)
• http://blogs.discovermagazine.com/notrocket
science/2012/11/20/the-deadliest-sea-snakeis-actually-two-look-alike-species/#more-7978
• http://tinyurl.com/SSSSSSSSNAKE
Divergent Evolution
• When one ancestral group evolves into two or more species, usually in
different habitats
• Features:
– Accounts for most evolutionary change
– Often due to ancestral spp. Increasing range / colonising new areas / habitats
(new ecological niches) The different conditions cause different selection
pressure  different genetic pathways  genetic isolation  speciation
• Alternatively:
– Sequential evolution: small changes build up over time until a new species
emerges (aka anagenesis, phyletic graduation)
– Budding: a new species branches off while the ancestral species remain
unchanged.
• Cladogenesis: When a whole new group of organisms evolves (eg primates)
Homologous Structures
“The structures shared by a set of related species because they have
been inherited, with or without modification, from their common
ancestor”
For example, the bones that support a bat's wing are similar in
structure, type and number to those of a human arm.
Differences are caused by differing natural selection pressures.
Eg selection for
traits enabling
flight favours thin
light bones in the
bat.
What pressures
result in the
other limbs
pictured?
Homologous Structures
• http://collections.tepapa.govt.nz/exhibitions/
Whales/Segment.aspx?irn=159
Adaptive Radiation
• “The diversification of a group of organisms into species filling different ecological
niches”.
• Can occur very rapidly, usually when a large number of ecological niches are vacant.
• Example par excellence:
– Dinosaur extinction 68mya opened up many niches for exploitation (eg Brontosaurus
death opened up a large browsing herbivore niche). Relatively non specialised mammals
(eg Megazostrodon were, as adaptable ‘generalists’, able to fill these niches quickly and
through natural selection speciate into new forms.
• Note: In a discussion you MUST involve natural selection AND niche.
– Eg for above example: variation in ancestral mammal species size  diet some bigger
& better able to use plants  survived better & reproduced more, passed those genes
on  further selection for various traits  elephant!


Asteroid: “Bye bye
dinos, vacate your
ecological niches!”
Mammals: “Thanks
a lot for the niches,
we will fill those!”
Megazostrodon model, Natural History Museum, London
• Other examples:
– Galapagos Finches: 1 South American finch evolved into 14 spp. occupying
different niches (desert, grassland…) on the Galapagos Islands
• NZ Examples:
– 100 spp. of Hebe plants (specialised into coastal, forest, alpine… niches)
– 10 spp. of Powelliphanta snails (+ subspecies, over different niches)
– NZ parrots (kakapo, kea, kaka) from one ancestor 100mya (forest vs alpine)
• Note: In some of these egs radiation was very fast (many vacant
niches) and involved the founder effect.
Powelliphanta spp.
Ale – see folder
for text
Weird Mammal Groups #1
• Ungulates (meaning roughly "being hoofed" or
"hoofed animal") a
– The odd-toed ungulates are browsing and grazing
mammals, such as horses, tapirs and rhinoceroses,
whose hooves each feature an odd number of toes
– Even toed ungulates: This group includes pigs,
peccaries, hippopotamuses, camels, chevrotains
(mouse deer), deer, giraffes, pronghorn, antelopes,
sheep, goats, and cattle.
Weird Mammal Groups #2
• Placentals
– Eg dog, horse
• Marsupials
– Eg wallaby
• Monotremes
– Eg platypus
Hawaiian
Honeycreepers
Hawaiian islands: volcanic
origin, variety of habitats.
In absence of other bird spp.
they radiated to fill
numerous niches
Galapagos Finch Niches
http://web.visionlearning.com/cus
tom/biology/animations/darwin_f
Anims…
inches_working.shtml
http://faculty.massasoit.mass.edu/whanna/1
22/page4/page7/page58/page58.html
http://faculty.massasoit.mass.edu/whanna/1
22/page4/page7/page58/page58.html
Co-Evolution
• Change in the genetic composition one species (or group) in response to
the change in another.
• Often occurs when close ecological interaction (symbiosis) occurs. Eg:
– Between parasite & host - exploitation
– With flower shape & pollinator - mutualism
– Between predator & prey – exploitation
• Examples:
– Lions: speed, strength, co-operative hunting (to catch gazelle)
– Gazelle: speed, size, strength, horns, darting behaviour (to escape lion)
• An “evolutionary arms race” one species evolves to respond to the other.
• Each party exerts selection pressures on the other  over time the spp
may become mutually dependent on each other.
• Relationship may become so close that extinction of one app means
extinction of the other
– Pollination Syndromes: where only one animal can pollinate only one specific
plant (often the pollinator beak shape co-evolves with the flower shape)
– Eg Adams’ mistletoe probably relied only on one NZ bird for pollination
(pollinator not yet confirmed) when this birds dropped in numbers Adams
mistletoe became extinct.
Adams Mistletoe
A victim of
pollination
syndrome?
Co-evolution example
Pseudomyrmex ant collecting protein-rich Beltian bodies from a bullhorn acacia, Costa Rica.
This is one of the most famous mutualisms of all, the relationship between Pseudomyrmex
ants and Acacia trees. The ants defend these small trees against herbivorous insects and
vertebrates. The ants also chew away and sting any encroaching plants, clearing an area
that may be up to 4 yd (4 m) in radius. In return, the plants give the ants food, such as the
yellow Beltian bodies seen here, and nectar from extra-floral nectaries. The Beltian bodies
contain proteins and lipids and are produced on the youngest and most delicate leaves. The
plants also produce thorns that the ants hollow out for nests.
Q. How could this evolve?
Anna's Hummingbird (Calypte anna) and bottlebrush sp.
The needle like beak and hovering ability of a
hummingbird is allows it to extract nectar (and pollinate)
funnel shaped flowers or flowers with no “landing pads”
Dactylanthus
taylorii
Pollinated by native bat with which it
shows coevolution.
Bat: nocturnal, blind BUT good sense
of smell
Flowers: drab, open at night, strong
scent (like a bat), wide shape (for
easy access)
Punctuated
Equilibrium
• Evolutionary model where there
are long periods of little change in
a spp punctuated by short bursts of
rapid change.
– Long periods of no evolutionary
change (stasis)
– Stasis punctuated by short periods of
evolution producing new species
rapidly
– Stimulus for evolution =
environmental change
– Species’ spend most of existence in
stasis
– If Correct: no transitional fossils,
sudden appearance of new types
Gradualism
• Evolutionary model where
the accumulation of changes
resulting in speciation occurs
slowly and steadily
– Evolution proceeds slowly but
continuously in response to
selection pressures
– Eventually changes in
adaptive characteristics
accumulate until speciation
occurs
– If correct transitional forms
should be seen (as is the case
with horse evolution)
– Example: Trilobites changed
gradually over three million
years
A Trilobite fossil: Kainops invius
Trilobites…
• Hard-shelled, segmented creatures lived over 520 million
years ago in Earth's ancient seas.
• Extinct before dinosaurs arrived
• Key creatures of the Paleozoic Era, (1st era with complex life)
• Fossils found in rocks in all continents
Body plan: 3 main parts – head,
segmented thorax, and a pygidium
(tail piece)
Trilobite means three lobed (see right).
Huge morphological diversity in
trilobites but all have this basic
structure
Size: 3mm – 300mm
www.trilobites.info
Evidence for evolution
• http://www.sumanasinc.com/webcontent/ani
mations/content/evolution/evolution.html
Poster Task
Rest of the period to:
• Present an A3 colour poster on an example of
convergent evolution, allopatric speciation or
sympatric speciation.
• You must:
•
•
•
•
Define the type of evolution speciation
Give a captioned example (no kea, kaka, butterfly)
Explain how this example came about
Name it!
Evidence for Evolution
1) Fossil Record
Fossil = preserved impression turned into rock or mineralised remains of past
organisms
Fossil record
Sedimentary rock forms in layers which may contain fossils. Older strata/fossils usually
found deeper (exception = after uplift).
This provides a record of:
Appearance/disappearance of species
Diversity at various times
Evidence of change of ancestral forms to modern forms
Fossil age can be determined by: dating rock layers, comparing to fossils in same strata
elsewhere.
Problems: Destruction of fossils (by subduction), some organisms
don’t fossilise well (eg soft bodied animals), most fossils are still
buried.
Archaeopteryx represents a transitional species between reptiles and birds
Fossil Record
2) Comparative Anatomy
“Comparison of body structures between different species”
Homologous Structures
• Similarity of structure between related species indicates evolution from a
common ancestor. Eg inheritance of pentadactyl limb in different mammals
Vestigial Organs
• Organs reduced in function size but remnant is shared with common ancestor
or closely related species. Eg human appendix = reduced caecum, lost function
of digesting cellulose, whale pelvis remnant - now no hind limbs.
How would natural selection against these structures operate?
Whale
What vestigial organs do kiwi have?
Snake
3) Biogeography
“The study of geographical distribution of species”
Species on a given island may more closely resemble species on a nearby
mainland rather than species on a distant island (even though the habitats
may be similar).
Eg Galapagos finches similar to mainland S.America finches, not similar to birds
1000s km away on Cape Verde islands. Adaptive radiation, allopatric speciation
important here.
Absence of certain taxa can be explained by their evolution after a
separation event. Eg placental mammals evolved after NZ split from Australia
85mya; this explains their absence in NZ. BUT we have examples of old
Gondwanan lineages eg tuatara, frogs.
Fossils of related organisms found on separate continents can be explained
by continental drift.
Eg glossopteris (a fern) evolved in Gondwana (350-230mya). Gondwana split up into
modern day Antarctica, Australia, India, Africa, S. America and fossils of it are found in
all locations. It couldn’t possibly have evolved after the split up and spread to each
location.
Therapods evolved in one place 140mya, spread out, continents split, therapods left
fossil remains of related species in spread apart locations. Much more plausible than a
recent independent origin of each species in each location.
Biogeography
Some organisms that evolved in Gondwana have
left fossils spread out amongst modern day
continents. Unlikely that they could have evolved
recently and spread out over the large distances
involved. Eg how could the land reptile
lystrosaurus get from India to Antarctica?
4) Molecular Biology
• Genetic Code: this is the base sequence of DNA. Organisms which
have a recent common ancestor will share more of the base
sequence than those that are unrelated. If the mutation rate is
known then base sequence difference between two species can
be extrapolated to determine when the last common ancestor
was;
• Proteins: more closely related species have more similarity in
their proteins (this reflects a similarity in the underlying DNA that
codes for the proteins).
• Hox Genes: a group of related genes that control structure and
orientation of organisms – critical for development and placing of
body parts. The homeobox is a sequence within a hox gene that
makes a protein that acts as a switch for the gene. The homeobox
has been found to be highly conservative (changes little) across
evolutionary lineages. A fly functions perfectly well with a chicken
hox gene in place of its own.
Interpretation:
The human/chimp
lineage split
relatively recently –
there has not been
enough time for
mutations to cause
differences in the
bases of the
cytochrome c gene
so the amino acid
sequence is identical
The human/yeast
lineage split a
relatively long time
ago, there has been
a lot of time for base
differences to
accumulate…
Rate of DNA hybridisation
Via the process of DNA
hybridization, scientists can
accurately determine the degree
of relatedness between various
groups of species. Matches in
base sequence between species
indicate a high degree of
relatedness. For example, in the
figure on the right you can see
that more matches are made
between a human and a chimp
than between a human and a
chicken. This indicates that the
human and the chimp shared a
more recent common ancestor
than the human and the chicken
and are closely related.
Don’t confuse the two!