What keeps a species from subdividing into other species? What causes a species to branch into two...
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QUESTIONS TO ANSWER What keeps a species from subdividing into other species? What causes a species to branch into two new species?
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Transcript of What keeps a species from subdividing into other species? What causes a species to branch into two...
QUESTIONS TO ANSWER
What keeps a species from subdividing into other species?What causes a species to branch into two new species?
HW
Finish Chapter 22 We will lecture Today and Tomorrow Friday we will begin the H-W Modeling
Lab 2-3 days
Quiz on CH 22 and 21 Next week
THE ORIGIN OF SPECIES
Speciation is the process by which one species splits into two or more species
MICRO VS MACROEVOLUTION
Microevolution consists of changes in allele frequency in a population over time
Macroevolution refers to broad patterns of evolutionary change above the species level
WHAT IS A SPECIES?
Biological Species Concept
OTHER SPECIES CONCEPTS
Morphological – Species based on shape, size, color, etc.
Ecological – based on niche Phylogenetic – based on evolutionary
relationships (smallest group of individuals that come from a common ancestor)
WEAKNESSES
Biological – asexual Ecological – gene flow Phyolgenetic – genetically
subjective Morphological – subjective bridge
WHAT HOLDS A SPECIES TOGETHER?
WHAT CAUSES SPECIATION?
Allopatric speciation
Sympatric speciation Polyploidy Habitat Differentiation Sexual Selection
FIGURE 22.3
Prezygotic barriers Postzygotic barriers
Habitatisolation
Temporalisolation
Behavioralisolation
Mechanicalisolation
Gameticisolation
Reducedhybrid
viability
Reducedhybridfertility
Hybridbreakdown
MATINGATTEMPT
FERTILI-ZATION
VIABLE,FERTILE
OFF-SPRING
(a) (c) (e) (f) (g) (h) (i) (l)
(j)
(k)
(d)
(b)
1. GEOGRAPHIC ISOLATION
A physical barrier separates (splits) the original population
As time passes, the environment may selects for different traits and the 2 populations become genetically different AND can’t reproduce
Barriers: Rivers, mountains, bodies of water
KAIBAB AND ABERT SQUIRRELS
- The Kaibab squirrel (Sciurus aberti kaibabensis) became geographically isolated from the common ancestor about 10,000 years ago.
- Its closest relative is the Abert squirrel (Sciurus aberti aberti)
- They live in opposite sides of the Grand Canyon
Kaibab Abert
Example: Emus, ostriches, rheas, Cassowaries,
Common ancestor lived in the continent of Gondwana (all southern continents together)
When Gondwana broke up, the populations separated and changed over time. All these birds are closely related but live far apart.
WRASSES: ORIGINAL POPULATION SPLIT UP WHEN THE ISTHMUS OF PANAMA WAS FORMED
- 2 SPECIES NOW, ONE ON EACH SIDE OF CENTRAL AMERICA
2. TEMPORAL ISOLATION (TIME OF REPRODUCTION)
Groups of individuals reproduce at different times. The genes of the 2 groups do not mix.
It is happening now with some of the migratory birds that decide not to migrate.
The birds that do not migrate start mating before the migratory ones come back.
Eventually they might become different enough that they may not recognize each other.
ROBINS USUALLY MIGRATE SOUTH TO WARMER CLIMATES. SOME ARE NOT MIGRATING. THEY REPRODUCE BEFORE THE MIGRATING INDIVIDUALS RETURN.
TEMPORAL ISOLATION
FIGURE 22.8Experiment
Mating experimentsafter 40 generations
Some flies raisedon starch medium
Results
Some flies raisedon maltose medium
Initial populationof fruit flies(Drosophila
pseudoobscura)
Female Female
Starch MaltoseStarch
population 1Starch
population 2
22
8 20
9 18 15
1512
Male
Male
Malt
ose
Sta
rch
Sta
rch
pop
ula
tion
1S
tarc
hp
op
ula
tion
2
Number of matingsin experimental group
Number of matingsin control group
FIGURE 22.8A
Experiment
Mating experimentsafter 40 generations
Some flies raisedon starch medium
Some flies raisedon maltose medium
Initial populationof fruit flies(Drosophila
pseudoobscura)
FIGURE 22.8B
Results
Female Female
Starch MaltoseStarch
population 1Starch
population 2
22
8 20
9 18 15
1512M
ale
Male
Malt
ose
Sta
rch
Sta
rch
pop
ula
tion
1S
tarc
hp
op
ula
tion
2Number of matings
in experimental groupNumber of matings
in control group
POLYPLOIDY
Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division
Polyploidy is much more common in plants than in animals
An autopolyploid is an individual with more than two chromosome sets, derived from one species
The offspring of matings between autopolyploids and diploids have reduced fertility
FIGURE 22.UN01Celldivisionerror
Tetraploid cell4n 12
New species(4n)
2n 6
2n
Gametes producedby tetraploids
An allopolyploid is a species with multiple sets of chromosomes derived from different species
Allopolyploids cannot interbreed with either parent species
FIGURE 22.9-1
Species A2n 6
Species B2n 4
Normalgameten 3
Unreduced gametewith 4 chromosomes
Meiotic error; chromosomenumber not reduced from 2n to n
FIGURE 22.9-2
Species A2n 6
Species B2n 4
Normalgameten 3
Hybrid with7 chromosomes
Unreduced gametewith 4 chromosomes
Meiotic error; chromosomenumber not reduced from 2n to n
FIGURE 22.9-3
Species A2n 6
Species B2n 4
Normalgameten 3
Normalgameten 3
Hybrid with7 chromosomes
Unreduced gametewith 7 chromosomes
Unreduced gametewith 4 chromosomes
Meiotic error; chromosomenumber not reduced from 2n to n
FIGURE 22.9-4
Species A2n 6
Species B2n 4
Normalgameten 3
Normalgameten 3
Hybrid with7 chromosomes
Unreduced gametewith 7 chromosomes
Unreduced gametewith 4 chromosomes
New species:viable fertile hybrid(allopolyploid)2n 10
Meiotic error; chromosomenumber not reduced from 2n to n
Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids
HABITAT DIFFERENTIATION
NA maggot fly can live on native hawthorn trees as well as more recently introduced apple trees
Normal lightMonochromatic
orange light
Experiment
P. pundamilia
P. nyererei
SEXUAL SELECTION
FIGURE 22.6
Under low predation:body shape that favorslong, steady swimming
(b)Under high predation:body shape that enablesrapid bursts of speed
(a)
SYMPATRIC SPECIATIONSEXUAL SELECTION
WHAT HYBRIDS TELL US ABOUT SPECIATION
Hyrbid Zone - region in which members of different species mate and produce hybrids
FIGURE 22.11
Fire-belliedtoad range Fire-bellied toad, Bombina
bombina
Yellow-belliedtoad range
Hybrid zone
Hybridzone
Fire-belliedtoad range
Yellow-belliedtoad range
Distance from hybrid zone center (km)2010010203040
0.99
0.9
0.1
0.01
Fre
qu
en
cy o
fB
. vari
eg
ata
-sp
ecifi
c a
llele
Yellow-bellied toad, Bombinavariegata
0.5
FIGURE 22.11B
Hybridzone
Fire-belliedtoad range
Yellow-belliedtoad range
Distance from hybrid zone center (km)2010010203040
0.99
0.9
0.1
0.01
Fre
qu
en
cy o
fB
. vari
eg
ata
-sp
ecifi
c a
llele
0.5
FIGURE 22.12-3
Isolatedpopulationdiverges. Hybrid
zone
Hybridindividual
Barrier togene flow
Gene flow
Population
FIGURE 22.12-4
Isolatedpopulationdiverges.
Possibleoutcomes:
Reinforcement
Fusion
Stability
Hybridzone
Hybridindividual
Barrier togene flow
Gene flow
Population
Reinforcement – hybrids less fit than the parent species
Natural selection reinforces reproductive barriers, and, over time, the rate of hybridization decreases
Where reinforcement occurs, reproductive barriers should be stronger for sympatric than for allopatric species
Fusion of the parent species into a single species may occur if hybrids are as fit as parents, allowing substantial gene flow between species
For example, researchers think that pollution in Lake Victoria has reduced the ability of female cichlids to distinguish males of different species
This might be causing the fusion of many species
FIGURE 22.13
Pundamilia nyererei Pundamilia pundamilia
Pundamilia “turbid water,”hybrid offspring from alocation with turbid water
Fusion
HOW FAST DO SPECIES FORM?Rates of Speciation
HOW FAST IS EVOLUTION?HOW FAST DO ORGANISMS CHANGE? Gradualism Punctuated Equilibrium
GRADUALISM
Organisms go through gradual and continuous change
PUNCTUATED EQUILIBRIUM Organisms go through fast periods of
change, followed by long periods of no change (according to fossil record)
PUNCTUATED EQUILIBRIUMPROPOSED BY STEPHEN JAY GOULD (1941-2002)
http://www.youtube.com/watch?v=8XggWLpupp4
GRADUALISM PUNCTUATED EQUILIBRIUM
Repeated Speciation and Macroevolution
THINGS WE’VE MISSED
Maintaining Variety Diploidy, heterozygote advantage,
Frequency dependant Selection Sympatric Speciation - Polyploidy Vestigial Structures
