Species Part B How do species occur Concept 242 Speciation can take place with or without geographic separation Speciation can occur in two ways Allopatric speciation Sympatric speciation ID: 725083
Download Presentation The PPT/PDF document "Chapter 24 The Origin of" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Chapter 24
The Origin of
Species
Part BSlide2
How do species occur?
Concept 24.2: Speciation can take place with or without geographic separation
Speciation can occur in two ways:
Allopatric
speciation
Sympatric
speciation
Both work through a block of gene flow between two populations.Slide3
Example
Pupfish populations in Death Valley.Generally happens when a specie’s range shrinks for some reason.Slide4
Fig. 24-5
(a) Allopatric speciation
(b) Sympatric speciationSlide5Slide6
Allopatric
SpeciationAllopatric
= other homeland
Ancestral population split by a geographical feature.
Comment – the size of the geographical feature may be very large or small.Slide7
The Process of
Allopatric Speciation
In
allopatric
speciation
, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations
The
definition of
barrier
depends on the ability of a population to disperse
Separate populations may evolve independently through mutation, natural selection, and genetic driftSlide8
Fig. 24-6
A. harrisi
A. leucurusSlide9
Evidence of
Allopatric Speciation
Regions with many geographic barriers typically have more species than do regions with fewer barriersSlide10
Fig. 24-7
Mantellinae
(Madagascar only):
100 species
Rhacophorinae
(India/Southeast
Asia): 310 species
Other Indian/
Southeast Asian
frogs
Millions of years ago (mya)
1
2
3
1
2
3
100
80
60
40
20
0
88 mya
65 mya
56 mya
India
MadagascarSlide11
Reproductive isolation between populations generally increases as the distance between them increasesSlide12
Fig. 24-8
Geographic distance (km)
Degree of reproductive isolation
0
0
50
100
150
250
200
300
0.5
1.0
1.5
2.0Slide13
Barriers to reproduction are intrinsic; separation itself is not a biological barrierSlide14
Fig. 24-9a
EXPERIMENT
Initial population
Some flies
raised on
starch medium
Mating experiments
after 40 generations
Some flies
raised on
maltose mediumSlide15
Fig. 24-9b
RESULTS
Female
Female
Starch
Starch
Starch
Maltose
population
1
population 2
Male
Starch
Maltose
Male
Starch
Starch
population 1
population 2
22
8
20
9
18
12
15
15
Mating frequencies
in experimental group
Mating frequencies
in control groupSlide16
Conditions Favoring
Allopatric Speciation
1. Founder's Effect - with the peripheral isolate.
2. Genetic Drift – gives the isolate population variation as compared to the original population.Slide17
Conditions Favoring
Allopatric Speciation
3. Selection pressure on the isolate differs from the parent population. (environment is different on the edges)Slide18
Result
Gene pool of isolate changes from the parent population and new species can form.Slide19
Sympatric Speciation
Sympatric = same homelandNew species arise within the range of parent populations.
Can occur
in
a single generation
.
In
sympatric speciation
, speciation takes place in geographically overlapping populationsSlide20Slide21
Plants
Polyploids may cause new species because the change in chromosome number creates
postzygotic
barriers.Slide22
Polyploidy
Polyploidy
is the presence of extra sets of chromosomes due to accidents during cell division
An
autopolyploid
is an individual with more than two chromosome sets, derived from one speciesSlide23
Polyploid
Types
1. Autopolyploid - when a species doubles its chromosome number from 2N to 4N.
2. Allopolyploid - formed as a
polyploid
hybrid between two species.
Ex: wheatSlide24
Fig. 24-10-1
2
n
= 6
4
n
= 12
Failure of cell
division after
chromosome
duplication gives
rise to tetraploid
tissue.
AutopolyploidSlide25
Fig. 24-10-2
2
n
= 6
4
n
= 12
Failure of cell
division after
chromosome
duplication gives
rise to tetraploid
tissue.
2
n
Gametes
produced
are diploid.
.
AutopolyploidSlide26
Fig. 24-10-3
2
n
= 6
4
n
= 12
Failure of cell
division after
chromosome
duplication gives
rise to tetraploid
tissue.
2
n
Gametes
produced
are diploid.
.
4
n
Offspring with
tetraploid
karyotypes may
be viable and
fertile.
AutopolyploidSlide27
AutopolyploidSlide28
An
allopolyploid is a species with multiple sets of chromosomes derived from different speciesSlide29
Fig. 24-11-1
Species A
2
n
= 6
Normal
gamete
n
= 3
Meiotic
error
Species B
2
n
= 4
Unreduced
gamete
with 4
chromosomes
allopolyploidSlide30
Fig. 24-11-2
Species A
2
n
= 6
Normal
gamete
n
= 3
Meiotic
error
Species B
2
n
= 4
Unreduced
gamete
with 4
chromosomes
Hybrid
with 7
chromosomes
allopolyploidSlide31
Fig. 24-11-3
Species A
2
n
= 6
Normal
gamete
n
= 3
Meiotic
error
Species B
2
n
= 4
Unreduced
gamete
with 4
chromosomes
Hybrid
with 7
chromosomes
Unreduced
gamete
with 7
chromosomes
Normal
gamete
n
= 3
allopolyploidSlide32
Fig. 24-11-4
Species A
2
n
= 6
Normal
gamete
n
= 3
Meiotic
error
Species B
2
n
= 4
Unreduced
gamete
with 4
chromosomes
Hybrid
with 7
chromosomes
Unreduced
gamete
with 7
chromosomes
Normal
gamete
n
= 3
Viable fertile
hybrid
(allopolyploid)
2
n
= 10
allopolyploidSlide33
AllopolyploidSlide34
Polyploidy is much more common in plants than in animals
Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploidsSlide35
Habitat Differentiation
Sympatric speciation can also result from the appearance of new ecological niches
For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple treesSlide36
Sexual Selection
Sexual selection can drive sympatric speciation
Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria Slide37
Fig. 24-12
EXPERIMENT
Normal light
Monochromatic
orange light
P.
pundamilia
P. nyerereiSlide38
Allopatric
and Sympatric Speciation: A Review
In
allopatric
speciation, geographic isolation restricts gene flow between populations
Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations
Even if contact is restored between populations, interbreeding is prevented Slide39
In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent
species
Sympatric speciation can result from polyploidy, natural selection, or sexual selectionSlide40
Adaptive Radiation
Rapid emergence of several species from a common ancestor ( often
Allopatric
speciation
)
Common in island and mountain top populations or other “empty” environments.Slide41
Mechanism
Resources are temporarily infinite.Most offspring survive.
Result - little Natural Selection and the gene pool can become very diverse.Slide42
When the Environment Saturates
Natural Selection resumes.
New species form rapidly if isolation mechanisms work
.
Examples
Galapagos – Finches
Usambaras
Mountains – African violetsSlide43
More next time