Download Chapter 24: The Origin of species

Chapter 24: The
Origin of species
-Macroevolution = the origin of new
taxonomic groups
-Speciation = origin of new species
-Anagenesis vs. Cladogenesis
I. What is a
Species?
1. Species Concepts
A.
B.
C.
D.
E.
Ecological Species Concept – defines a
species based on its niche
Pluralistic Species Concept – factors that
make species vary
Morphological Species Concept – unique
structural features
Genealogical Species Concept – unique
genetic history / one tip on the branching tree
of life
Biological Species Concept – potential to
interbreed and produce viable, fertile offspring
/ hinges on reproductive isolation or barriers
2. Isolation Barriers

A.
Reproductive Barrier – any factor that impedes
2 species from producing fertile, viable
offspring
Prezygotic – hinder fertilization of ova
- habitat iso – live in different habitats
- behavioral iso – signals and behaviors
- temporal iso – different times of day or year
- mechanical iso – anatomical incompatibility
- gametic iso – gametes don’t fuse
2. Isolation Barriers
B.
Postzygotic Barriers – prevents hybrid zygote
from developing
- Reduced Hybrid Viability – aborted embryo
- Reduced Hybrid Fertility – sterile offspring /
meiosis failure
- Hybrid Breakdown – viable F1, F1s produce
sterile or feeble offspring
II. How is a Species
Made?
1. Allopatric Speciation




Speciation takes place in populations with
geographically separate ranges
Mountain range, land bridge, land production
Increases when a population is small and
isolated
Can be observed in ring species where bottom
organisms can’t breed
1. Allopatric Speciation
A.
B.
Adaptive Radiation – many diversely
adapted species from a common
ancestor
Both pre and post zygotic barriers may
evolve from allopatric speciation
Sweet Video
2. Sympatric Speciation


A.
Speciation takes place in geographically
overlapping populations
Result from chromosomal change, nonrandom mating
Polyploid Speciation in Plants
- extra sets of chromosomes
- autopolyploid – more then 2 sets
- allopolyploid – 2 species make a polyploid
hybrid
Autopolyploid
Allopolyploidy
2. Sympatric Speciation
B.
Animals and Sympatric Speciation
- Genetic factors cause dependence on
resources not used by parents
- Preferences for mates color or looks
(non-random mating) / cause behavioral
isolation
3. Speed of Speciation
A.
B.
Gradualism – small
changes over time
Punctuated
Equilibrium – rapid
change and then no
change
III. Speciation to
Macroevolution
1. Evolution Novelties Come From
Older Structures
A.
B.
Eye Spots ---- Eyes
Exaptations –
structures that
evolve in one
context but become
co-opted for another
function / ex. Hollow
bones
2. Evo-Devo
Looking at evolution biology and development of
organisms together

Genes that control development play a major role in
macroevolution
A.
Allometric Growth – growth rates at different times
during development / change the growth rates a little
(genes) and it can really change the adult / Type of
heterochrony
B.
Heterochrony – evolutionary change in the rate or
timing of developmental events / salamander feet
- paedomorphosis – reproductive development
accelerates compared to somatic development / adults
retaining juvenile ancestral traits
C.
Homeotic Genes – determine basic features where
things develop / Hox gene changes leg buds
Kinda Sweet Video

Allometric Growth
Heterochrony
Hox Gene
3. Trends
Trends ≠ goal or end point
 Bush growing in all directions not just one
 Species selection – idea that the species
that endure the longest and generate the
greatest number of new species determine
the direction of evolutionary trends /
people argue that it is gradual changes
that cause the trends not numbers of
individuals
