Transcript Chapter 24 ppt

Chapter 24 ~Macroevolution
Origin of Species
What is a species?
A population whose
members have the
potential to interbreed
and produce viable,
fertile offspring
Horse
+
Zebra
Zorse = not-fertile
Patterns of Evolution
Divergent Evolution
• 2 or more species
originate from a
common ancestor
Patterns of Evolution
Convergent Evolution
• 2 unrelated species
share similar traits
due to adaptation to
similar environments
• Unrelated species will
never evolve into a
single species
Patterns of Evolution
Parallel Evolution
• 2 or more related
species make similar
evolutionary changes
Patterns of Evolution
Co-Evolution
• Two interacting
species evolve
together
Macroevolution
For macroevolution to
• Large-scale
occur, two populations
evolution:
must be reproductively
– The descent of
isolated (or separated)
different species
from one another
from a common
ancestor over
Over time, the two populations
many generations.
of beetles are eventually
considered different species,
since they can no longer
produce viable, fertile offspring.
Pre-zygotic Isolating Mechanisms
Isolating mechanisms that prevent
fertilization
Ova/egg
Pre-zygotic Isolating Mechanisms
1) Habitat Isolation
2 populations live in
different habitats and
rarely meet
Ex. Terrestrial vs. Aquatic Garter Snakes
Pre-zygotic Isolating Mechanisms
2) Behavioral Isolation
2 populations can
not recognize
differences in
courtship rituals
2 subspecies of tropical finches
have been separated enough to
have variations in song that they
do not recognize
Pre-zygotic Isolating Mechanisms
3) Temporal Isolation
2 populations that
breed during
different times of day
or seasons
Day vs. Night Blooming Lily
Pre-zygotic Isolating Mechanisms
4) Mechanical Isolation
incompatible sexorgans/genitalia
5) Gametic Isolation
Sperm can not
survive in the
reproductive tract of
females or gametes
fail to recognize each
other
Post-zygotic Isolating Mechanisms
Fertilization is successful, but zygote is
prevented from developing into a viable
adult
Ova/Egg
Post-zygotic Isolating Mechanisms
1) Hybrid Inviability – genetic incompatibility
causes early miscarriage
2) Hybrid Sterility - Hybrid is viable, but
sterile
3) Hybrid Breakdown – Hybrid is viable and
fertile, but its offspring is sterile
Modes of Speciation
(How new species are formed)
1) Allopatric Speciation
2) Adaptive Radiation
3) Sympatric Speciation
Allopatric Speciation
~ “other”
~ “homeland”
When a speciation
occurs due to
geographic isolation
between two
populations
Back to Modes of Speciation
Adaptive Radiation
• Type of allopatric speciation
• Rapid evolution of many species from a
single ancestor due to colonization of an
area w/diverse conditions (ex. Darwin’s
finches)
Back to Modes of Speciation
Sympatric Speciation
• When new species are formed w/o a
geographic barrier (more common in
plants)
• This can an occur due to the following
reasons:
– Polyploidy
– Allopolyploidy
– Balanced Polymorphism
Sympatric Speciation
(due to polyploidy)
• Mutant condition occurs when a non-disjunction
error in meiosis causes gametes that are diploid.
• Mutant zygotes are triploid (3N) or tetraploid
(4N) as a result and can propagate a new
species
Sympatric Speciation
(due to allopolyploidy)
• Type of hybridization
• When two different species interbreed and
combine their chromosomes
• Usually sterile, but can breed new species
asexually
Sympatric Speciation
(due to balanced polymorphism)
• When there are different phenotypes in a
population, members can self-isolate and
“selectively breed” with those of their own.
• Over time, two populations of differing
phenotypes (ex. colors) can evolve into
two different species
Does macroevolution occur
gradually or suddenly?
Evolution
occurs
to
Evolution
occurs due to
Two
models
ofdue
evolutionary
thought:
-abrupt
changes in the
-gradual accumulation
1) Gradualism
environment (ex.
of small changes over
2) Punctuated
Catastrophes)
that Equilibrium
time
drives rapid speciation
-New species appear
quickly, then changes
very little over time
** supported by fossil
evidence
Gradualism
** not supported by
fossil evidence, since
existence of
“intermediate” fossils
are few or inadequate
to support the theory
[;’p
Punctuated
Equilibrium