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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chapter 24 The Origin of Species
TOP 5
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1. Ways at Classifying Species
• Biological species concept
– Population that has the potential to interbreed and produce viable, fertile offspring but unable to produce viable fertile offspring with members of other populations
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Other Species Concepts
• Morphological
– Based on shape, size, etc.
• Ecological
– in terms ecological niche
• Phylogenetic
– in terms of unique genetic history
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2. Biological Species Barriers
• Prezygotic barriers
– Impedes fertilization of ova
• Postzygotic barriers
– Prevents hybrid zygote from developing
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Prezygotic and postzygotic barriers
Figure 24.4
Prezygotic barriers impede mating or hinder fertilization if mating does occur
Individualsof differentspecies
Matingattempt
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION
(b)
(a)(c)
(d)
(e)
(f)
(g)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Viablefertile
offspring
Reducehybrid
viability
Reducehybridfertility
Hybridbreakdown
Fertilization
Gameticisolation
GAMETIC ISOLATION REDUCED HYBRID VIABILITY
REDUCED HYBRID FERTILITY HYBRID BREAKDOWN
(h) (i)
(j)
(k)
(l)
(m)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(a) Allopatric speciation. A population forms a new species while geographically isolated from its parent population.
(b) Sympatric speciation. A smallpopulation becomes a new specieswithout geographic separation.
Figure 24.5 A, B
Speciation can occur in 2 ways
– Allopatric
– Sympatric
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3. Formation of Species: Allopatric
• Allopatric speciation
– Population is divided into 2 or more geographically isolated subpopulations
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 24.6
A. harrisi A. leucurus
• Geographic separation
evolutionary change during the period of separation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Allopatric speciation
– Reproductive isolation
Figure 24.7
Initial population of fruit flies(Drosphila
Pseudoobscura)
Some fliesraised on
starch medium
Some fliesraised on
maltose mediumMating experimentsafter several generations
EXPERIMENT Diane Dodd, of Yale University, divided a fruit-fly population, raising some populations on a starch medium and others on a maltose medium. After many generations, natural selection resulted in divergent evolution: Populations raised on starch digested starch more efficiently, while those raised on maltose digested maltose more efficiently. Dodd then put flies from the same or different populations in mating cages and measured mating frequencies.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3. Formation of Species: Sympatric
• Sympatric speciation
– Geographically overlapping populations
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Polyploidy
– Extra sets of chromosomes f/ accidents during cell division
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Autopolyploid
– More than two chromosome sets, f/ same species
Figure 24.8
2n = 64n = 12
2n
4n
Failure of cell divisionin a cell of a growing diploid plant afterchromosome duplicationgives rise to a tetraploidbranch or other tissue.
Gametes produced by flowers on this branch will be diploid.
Offspring with tetraploid karyotypes may be viable and fertile—a new biological species.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Allopolyploid
– Multiple sets of chromosomes derived from different species
Figure 24.9
Meiotic error;chromosomenumber notreduced from2n to n
Unreduced gametewith 4 chromosomes
Hybrid with7 chromosomes
Unreduced gametewith 7 chromosomes Viable fertile hybrid
(allopolyploid)
Normal gameten = 3
Normal gameten = 3
Species A 2n = 4
Species B 2n = 6
2n = 10
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Goat’s Beard
• Illustration of an Allopolyploid
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Sexual Selection
• Cichlid fish
– Sympatric speciation f/ nonrandom mating due to sexual selection
Figure 24.10
Researchers from the University of Leiden placed males and females of Pundamilia pundamilia and P. nyererei together in two aquarium tanks, one with natural light and one with a monochromatic orange lamp. Under normal light, the two species are noticeably different in coloration; under monochromatic orangelight, the two species appear identical in color. The researchers then observed the mating choices of the fish in each tank.
EXPERIMENT
P. nyererei
Normal lightMonochromatic
orange light
P. pundamilia
Under normal light, females of each species mated only with males of their own species. But under orange light, females of each species mated indiscriminately with males of both species. The resulting hybrids were viable and fertile.
RESULTS
The researchers concluded that mate choice by females based on coloration is the main reproductive barrier that normally keeps the gene pools of these two species separate. Since the species can still interbreed when this prezygotic behavioral barrier is breached in the laboratory, the genetic divergence between the species is likely to be small. This suggests that speciation in nature has occurred relatively recently.
CONCLUSION
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Allopatric speciation
– Speciation due to geographic isolation
• Sympatric speciation
– Barrier isolates a subset of a population without geographic separation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
5. Adaptive Radiation
• Adaptive radiation
– Evolution of diversely adapted species from a common ancestor upon introduction to new environment
Figure 24.11
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Hawaiian archipelago
– Showcase of adaptive radiation
Figure 24.12
Dubautia laxa
Dubautia waialealae
KAUA'I5.1
millionyears O'AHU
3.7millionyears
LANAI
MOLOKA'I
1.3 million years
MAUI
HAWAI'I0.4
millionyears
Argyroxiphium sandwicense
Dubautia scabra Dubautia linearis
N