Transcript Macroevolution

Macroevolution
Speciation
• The formation of new
species
• Species: A group of
individuals capable of
interbreeding
• Populations are isolated,
then there are changes in
allele frequencies. The
populations diverge and
over time they can become
distinct species.
Reproductive Isolation
• Prezygotic Isolation - when
individuals of different species are
prevented from mating
• Allopatric Speciation
•
Habitat Isolation – geographic
barrier
• Sympatric Speciation
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Behavioral Isolation – little or no
sexual attraction
Temporal Isolation –
mating/flowering occurs at different
times
Mechanical Isolation – structural
differences in genitalia or flowers
prevent gamete transfer
Gametic Isolation – female and
male gametes fail to attract each
other/inviable
DISPERSAL AND COLONIZATION CAN ISOLATE POPULATIONS.
Island
Continent
1. Start with one continuous
2. Island population begins
3. Finish with two populations
population. Then, colonists
float to an island on a raft.
to diverge due to drift and
selection.
isolated from one another.
VICARIANCE CAN ISOLATE POPULATIONS.
River
1. Start with one continuous
2. Isolated populations begin
3. Finish with two populations
population. Then a chance
event occurs that changes
the landscape (river changes
course.)
to diverge due to drift and
selection.
isolated from one another.
Adaptive Radiation
• Rapid evolution of many species from single common ancestor
• Diverse geographical or ecological conditions
Reproductive Isolation
• Postzygotic Isolation - when
individuals from different
populations do mate, but the
hybrid offspring produced have
low fitness
• Hybrid Inviability –
zygotes fail to develop
• Hybrid Sterility – fail to
produce functional
gametes
• Hybrid Breakdown –
offspring of hybrids have
reduced viability of fertility
• Tigon
– Male tiger
– Female lion
• Liger
– Male lion
– Female tiger
• Litigon
– Male lion
– Female Tigon
– RARE!
• Only exist in captivity
(some are zoo
mistakes from not
keeping species
separate)
• Subspecies are populations that live in
discrete geographic areas and have their own
identifying traits but are not distinct enough to
be considered a separate species
•Soapberry bugs
feed and mate on
certain host plants
including the
soapberry tree. They
began to feed on
new species of
plants that were
introduced to their
environment. These
plants had fruits
much smaller than
those of the native
plant species.
Feeding
on the
fruit of
a native
species
Feeding on
the fruit of
a
nonnative
species
Nonnative fruits are much smaller than native fruits.
Nonnative
plant
(small fruit)
Native
plant
(large fruit)
Evidence for disruptive selection on beak length
Short-beaked
population
growing on
nonnative
plants
Long-beaked population
growing on native plants
•
Possible outcomes of secondary contact
between two related populations:
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Fusion of the populations
Reinforcement of divergence
Founding of stable hybrid zones
Extinction of one population
Origination of a new species
Reinforcement of reproductive isolation
(sympatric) of rhinocerous beetles (Laos)
Polyploidy
• a species may originate from accident
during division resulting in extra set of
chromosomes
•Can lead to sympatric speciation
• Autopolyploid – Parents of same species
produce offspring with a doubling of
chromosome number due to nondisjunction
• Allopolyploidy - Parents that belong to
different species produce offspring in which
chromosome number doubles
Autopolyploidy
Allopolyploidy
Allopolyploidy may occur after two species hybridize.
Many diploid plant species
have closely related
polyploid species,
supporting the claim that
speciation by polyploidy is
important in plants.
In summary, speciation by
polyploidization is driven
by chromosome-level
mutations and occurs in
sympatry.
Species 2
Species 1
Meiosis
Haploid gametes
Fertilization
These chromosomes
do not synapse and
separate normally
Error in meiosis or mitosis
Allopolyploid
cell—now each
chromosome has
a homolog
Meiosis
Diploid gametes
(can fuse to form a
tetraploid individual)
Macroevolution
• Microevolution - how populations of
organisms change from generation to
generation and how new species
originate
• Ex: a change in a species’ coloring
or size
• Macroevolution - the pattern of
changes over broad periods of time
Theories on how to interpret fossil record:
Phyletic Gradualism – gradual accumulation of small
changes; states fossil record is incomplete
Punctuated Equilibrium – long periods of stability followed
by short periods of rapid evolution; explains why few
intermediate fossils are found
The Oparin-Haldane Theory
• In the early Earth, simple organic molecules were
able to form only because oxygen was absent.
• Presence of CO, CO2, H2, N2, H2O, S, HCl, HCN
• Abiotic synthesis of organic monomers
• Impossible now with an oxygen-rich atmosphere due to photosynthesis
The Miller and Urey Experiment
Reaction:
– Heated “sea”
– Made an “atmosphere”
– Made “lightning” (electric
sparks) in atmosphere
– Cooled the atmosphere,
creating “rain” with dissolved
compounds
• When analyzed, Miller and
Urey found all 20 amino
acids, several sugars,
lipids, purines and
pyrimidines of DNA and
RNA, and ATP
The Origin of Life
Formation of:
1. Earth and atmosphere (hot gasses, little/no oxygen)
2. Seas (cooling Earth – gasses condensed)
3.
Organic monomers (“organic soup”)
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Energy from UV, lightning, etc.
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See Oparin-Haldane Theory & Miller-Urey
experiment
4.
Polymers and self-replicating molecules (proteinoids)
5.
Protobionts
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6.
Precursors to cells; membrane-bound,
unable to reproduce
Primitive heterotrophic prokaryotes
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Competition for resources increased; natural
selection favored those more successful at
obtaining food (from “soup”)
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3.5 billion years ago
7.
Primitive autotrophic prokaryotes
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8.
Photosynthesis ability from mutation
Oxygen and ozone layer (from photosynthesis)
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9.
As UV light is prevented from reaching
surface, decreased abiotic synthesis of
organic molecules
Eukaryotes
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2.1 billion years ago
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See Endosymbiosis Hypothesis
Characteristics Of The
Earliest Organisms
• Prokaryotic
• Small (surface to volume
ratio)
• Unicellular
• Heterotrophic
• Asexual reproduction
• Organic monomers
• Anaerobic
• Aquatic
• ATP
• DNA or RNA
• mRNA for information
transfer
• tRNA to carry amino acids
• Ability to mutate
• Ability to synthesize proteins
Endosymbiotic Theory
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Origin of Eukaryotes
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Explains larger, more complex cells with endomembranes
Mitochondria and chloroplasts are similar to some bacteria
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Similar size
Own circular DNA with similar gene sequences
Reproduce independently
Double membranes (much like a vesicle after endocytosis)
“A cell living within a cell” – mutualism