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Evolution Milestones
Review
What are the limits or boundaries of scientific investigation and explanation?
Define the following terms as they are used in science:
Hypothesis
Law
Theory
What is the difference in how the word ‘theory’ is used in everyday language and how it is used in
science?
Explain the significance of the following terms as they apply to the nature of science:
Scientific Hypothesis
Evidence-Based
Peer Review
New Information
Mechanism of Evolution
Compare the following:
Lamarck’s explanation of Evolution: (Acquired Traits)
Darwin’s theory of Evolution: (Natural Selection)
How does this cartoon illustrate a common misconception about how natural selection works?
What are the origins of evolutionary thought? (Timeline on page 374)
Evolution is a change in allele frequencies over successive generations.
What are five things that can cause these gene frequencies to change from one generation to the
next?
(Remember Hardy-Weinberg’s five rules for a population that doesn’t evolve.)
1.
2.
3.
4.
5.
Compare and contrast the following terms:
Artificial Selection
Natural Selection
Which term means the creation of new species?
What is a scenario that can cause this event to happen?
Answer the following questions using either cladogram:
Which species is equally related to all the others?
Which species is most closely related to species F?
Which species might be most unlike all the others?
Use the cladogram below to answer the following questions:
Which derived characteristic is shared by all organisms on the cladogram except the hagfish
and the perch?
Is the lizard more closely related to the pigeon or the salamander?
Which event is illustrated in the above picture?
For each type of evidence listed below, explain how it shows the evolutionary history of life.
Fossil Record
DNA Analysis (Molecular)
Morphology (Body Shapes)
Embryology
Viral Evolution
e.g. HIV, Flu
Antibiotic Resistance in Bacteria
What are the two methods for describing the age of a fossil?
Label the diagram with the correct metho
List the categories of taxonomy starting with the broadest and ending with the most specific:
(Ch 18)
What is a phylogenetic tree???
Draw a Cladogram for the major plant phyla: (Ch 18 & 22)
Types of Speciation:
Speciation is of following types.
1. Allopatric Speciation (alios— other, patria— native land):
In this type of species formation, a part of the population becomes geographically
isolated from the main population. The population becomes entirely separated and
finally constitutes a new species. Thus geographic isolation brings about allopatric
speciation. An important example of this type of speciation is formation of Darwin’s
finches that formed separate species in the Galapagos Islands (Fig. 7.55A).
2. Sympatric Speciation (sym— together, patria— native land):
In this type of species formation, a small segment of the original population becomes
isolated reproductively. As the isolating mechanism comes into force, a new
subspecies emerges. In due course of time a new species is formed. Thus sympatric
speciation is the formation of species within a single population without geographical
isolation. The reproductive isolation brings about sympatric speciation (Fig. 7.55B).
3. Parapatric Speciation:
It separates adjacent population. Parapatric speciation takes place when a
population of a species enters a new niche or habitat. It occurs only at the edge of
the parent species range. Although there is no physical barrier between these
populations, yet the occupancy of a new niche results as a barrier to gene flow
between the population of new niche. Two species are produced due to reproductive
isolation from single one. Such type of speciation is found in flightless grasshoppers,
smails and annual plants.
Factors Influencing Speciation:
Following factors influence the speciation:
(i) Mutation
(ii) Recombination
(iii) Natural selection
(iv) Hybridization
(v) Genetic drift
(vi) Polyploidy (to be described) and
(vii) Isolation.
Speciation is the formation of one or more new species from an existing species.
A species is a collection of demes. The deme is a group of populations with common
gene pool.
Types of Speciation:
Speciation is of following types.
1. Allopatric Speciation (alios— other, patria— native land):
In this type of species formation, a part of the population becomes geographically
isolated from the main population. The population becomes entirely separated and
finally constitutes a new species. Thus geographic isolation brings about allopatric
speciation. An important example of this type of speciation is formation of Darwin’s
finches that formed separate species in the Galapagos Islands . Draw an example
2. Sympatric Speciation (sym— together, patria— native land):
In this type of species formation, a small segment of the original population becomes
isolated reproductively. As the isolating mechanism comes into force, a new
subspecies emerges. In due course of time a new species is formed. Thus sympatric
speciation is the formation of species within a single population without geographical
isolation. The reproductive isolation brings about sympatric speciation
Draw an example
3. Parapatric Speciation:
It separates adjacent population. Parapatric speciation takes place when a
population of a species enters a new niche or habitat. It occurs only at the edge of
the parent species range. Although there is no physical barrier between these
populations, yet the occupancy of a new niche results as a barrier to gene flow
between the population of new niche. Two species are produced due to reproductive
isolation from single one. Such type of speciation is found in flightless grasshoppers,
smails and annual plants.
Draw an example
Factors Influencing Speciation:
Following factors influence the speciation:
(i) Mutation
(ii) Recombination
(iii) Natural selection
(iv) Hybridization
(v) Genetic drift
(vi) Polyploidy (to be described) and
(vii) Isolation.
Polyploidy:
Increase in number of chromosomes or chromosome sets is called polyploidy.
Polyploidy does not occur commonly in animals. The additional chromosomes in
animals are mostly lethal. However, polyploidy occurs commonly in plants.
Polyploidy has played an important role in plant evolution.
There are many common polyploidy plants. Tobacco is a polyploidy that evolved by
the hybridization of two smaller species. In wheat, there are species with 14, 28 and
42 chromosomes. Different varieties of wheat have been obtained by polyploidy.
REPRODUCTIVE ISOLATING MECHANISMS
The biological definition of a species is a group of similar organisms that can
interbreed to produce fertile, viable offspring. Some extend this to say that this
reproduction must occur under natural, not artificial (e.g., in captivity) situations.
When an ancestral species gives rise to two new species, what determines whether the
two new species can reproduce?
Consider the mechanisms that restrict gene flow: reproductive isolating
mechanisms.
PREZYGOTIC ISOLATING MECHANISMS prevent the formation of
viable zygotes.

Ecological Isolation
The geographic ranges of two species overlap, but their ecological needs or breeding
requirements differ enough to cause reproductive isolation.
example
In central and northern California, the Red-legged Frog (Rana aurora) breeds
in fast-moving, ephemeral streams.
Artificially introduced Bullfrogs (Rana catesbiana) breed in permanent ponds.
The metamorphosis times of the two species' tadpoles are correspondingly
different.

Temporal Isolation
two species whose ranges overlap have different periods of sexual activity or
breeding seasons
example
The Red-legged Frog (Rana aurora, left) breeding season lasts from January to
March.
The closely related Yellow-legged Frog (Rana boylii, right) breeds from late
March through May.
example
Drosophila persimilis breeds in early morning, while closely
related Drosophila pseudoobscura breeds in the afternoon
+
=

Behavioral Isolation
Species with complex courtship rituals (breeding calls, mating dances, etc.) usually
exhibit a stereotyped "give-and-take" between male and female before actual
mating takes place.
 Superb Bird of Paradise
 Teminck Tragopan
 Superb Lyrebird
 Malaysian Fireflies
These rituals prevent the wasted effort of mating with a partner who will not produce
fertile, viable offspring with you.

Mechanical Isolation
Morphological differences prevent mating/pollination.

The amazing partnership of the Bucket Orchid and Orchid Bee is so precise that if either
one went extinct, the other would follow,. No other orchid can possibly crosspollinate the Bucket Orchid.

In some snail species, the direction of shell coiling is controlled by a single
(maternal effect) gene. Snails with left-coiling shells cannot mate with snails having
right-coiling shells. This could eventually lead to further differentiation and
speciation. example

Gametic Isolation
In this case, sperm and ova of the two species are chemically (genetically)
incompatible, and will not fuse to form a zygote.
example
Sea urchins do not mate. They broadcast their gametes into the ocean where sperm
and eggs fuse to form zygotes and then develop into larvae. The Giant Red Urchin
(Strongylocentrotus franciscanus and Purple Urchin (Strongylocentrotus purpuratus)
cohabit the rocky intertidal along the western U.S., but they do not interbreed. Their
gametes are genetically/chemically incompatible, maintaining species integrity.
POSTZYGOTIC ISOLATING MECHANISMS prevent hybrids from passing on
their genes.

Hybrid Inviability
A zygote may form with union of sperm and egg from the two species, but the
embryo dies after a few cell divisions. The genetic information from male and
female parents is insufficient to carry the organism through morphogenesis.
x
=

Hybrid Sterility
Viable hybrid is produced (often physically more vigorous than either parent), but is
unable to reproduce due to meiotic problems.
examples

Horse (Equus caballus) x Donkey (Equus asinus) = Mule or Hinny
Other Interesting Hybrids (or are they?)

Hybrid Breakdown
successive generations of hybrids suffer greatly lowered fertility --> sterility.
Eventually, they are selected out of the population.
Hybridization Between Species
If there is interbreeding between two closely related species, there are several
possible outcomes.




Species Reinforcement - hybrids have lower fitness than either parent
species; reproductive isolation is maintained due to lack of hybrid
survival/reproduction.
Species Fusion - two species in a hybrid zone may have weak reproductive
isolating barriers, and the two species may, over time, eventually share a
common gene pool.
Species Stability/Hybrid Equilibrium - Hybrids are continually produced by the
two parent populations in a hybrid zone. A narrow hybrid zone can foster
constant hybridization with reduced hybrid survival (e.g., Bombina) hybrid zone in
Eastern Europe.
Hybrid Speciation - Hybrids may actually be reproductively superior to parent
populations, and if they tend to breed with each other, this can result in what
could be termed hybrid speciation.