Macroevolution
Macroevolution is the study of major
biological changes evident in the fossil
record
Includes the following:
1.
Multiplication of species
2.
Origin of structures like feathers and
large brains
3.
Diversification of species – like flowers
4.
Mass extinctions that lead to explosions like the explosion of mammals after the
dinosaurs became extinct
speciation
Speciation is the origin of new species
Branching vs. non-branching
Branching – a lineage is split into two
or more species
Non-branching – initial species
becomes new species
Anagenesis vs.
Cladogenesis
The Origin of Species
Biological species concept – groups of
interbreeding natural populations
whose members ONLY breed with
each other to create fertile offspring.
What keeps members of different
species apart?
Reproductive Barriers
Prezygotic barriers – occur before
conception
Post-zygotic barriers – occurs after
conception
Pre-zygotic Barriers
Temporal Isolation –
mating or flowering
occur at different time
of the year/day
Ex. Western spotted
skunks breed in fall,
while eastern spotted
skunks breed in the
late winter
Habitat Isolation –
species living in the
same region may
occupy different
habitats
Ex. Some Garter snakes
live in water/some on
land
Behavioral
Isolation-courtship
rituals are very
specific
Ex. Birds
Mechanical
isolation-structural
differences in
genitalia or flowers
prevent copulation
or pollen transfer
Ex. Insects and flowers
Gametic isolationmale sperm cannot
fertilize the egg
Post-zygotic Barriers
Hybrid Inviability – hybrid zygotes
fail to develop or reach sexual
maturity
Hybrid Sterility – Hybrid individuals
fail to produce young
Speciation
When a
population is
somehow severed
from the parent
population and
over time its gene
pool is altered.
Allopatric and
sympatric
Allopatric speciation
Isolation is the result of a
geographic barrier
Ex. Galapagos finches
True speciation only occurs if the
remaining populations will NOT
breed
allopatric
Sympatric
When a sub-population arises in the
midst of the parent population
Many plant species have accidental
polyploidy in meiosis. They produce
zygotes with multiple sets of
chromosomes.
They can no longer reproduce with
parental generation.
Evolution of Wheat
What is the tempo of
speciation?
Gradual vs. punctuated
Punctuated equilibrium model –
species most often diverge in spurts of
rapid change instead of slow and
gradually.
Over a few to ten thousand years,
genetic drift and natural selection can
change small, isolated species
Punctuated
Equilibrium
Archaeopteryx
Exaptation
Term used to describe a structure
that evolves in one context, but
becomes adapted for another.
However, natural selection cannot
anticipate future need
Ex. Light bones in reptiles
Evo-Devo
How do evolution and development
interface?
Genes control the development of an
organism from zygote to adult
Turning these genes on and off at
certain times can have a profound
effect on development.
Paedomorphosis – the retention of
juvenile features as an adult
Ex. axototl
Axototl
Chimpanzee vs. human
skulls
We retain a skull
more like that of
our fetal skull
History of biological
diversity
Macroevolution is tied to the history
of the Earth
Fossils are recovered from various
sources
Sedimentary rocks
Skulls
Petrified trees
Tracks
Body parts
Amber
Geological Time Scale
Four eras – Precambrian, Paleozoic,
Mesozoic, Cenozoic
Fossils are dated by carbon dating
Handout
At the end of the paleozoic era (250mya),
Pangaea was formed.
The formation of pangaea reduced
coastline and changed the environment
for many terrestrial species.
Changing ocean currents killed many
marine species
Breaking of Pangaea
180 MYA during the mesozoic
Caused major geographic isolation
Continental drift
Patterns of Evolution
Divergent evolution – when two
isolated population evolve
independently (Ex. Brown and
polar bears)
Adaptive radiation – rapid
evolution of a variety of species
from a single ancestor (ex.
Darwin’s finches)
Convergent Evolution – when two
organisms without a common
ancestor occupy the same niche, so
they have the same characteristics.
(ex. Porpoise and penguin)
Patterns cont.
Parallel Evolution – two related
species who have made similar
evolutionary changes. Ex. Placental
and marsupial wolf
Co-evolution – predator/prey
relationships
Adaptive Radiation
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