Ch 24 – Origin of Species. Overview: The “Mystery of Mysteries” Overview: The “Mystery of...
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Transcript of Ch 24 – Origin of Species. Overview: The “Mystery of Mysteries” Overview: The “Mystery of...
Overview: The “Mystery of Overview: The “Mystery of Mysteries”Mysteries”
Darwin explored the Galápagos Darwin explored the Galápagos IslandsIslands And discovered plants and animals And discovered plants and animals
found nowhere else on Earthfound nowhere else on Earth
Figure 24.1
Concept 24.1: The biological species Concept 24.1: The biological species concept emphasizes reproductive concept emphasizes reproductive isolationisolation
SpeciesSpecies Is a Latin word meaning “kind” or Is a Latin word meaning “kind” or
“appearance”“appearance”
The Biological Species The Biological Species ConceptConcept The biological species conceptThe biological species concept
Defines a species as a population or group Defines a species as a population or group of populations whose members have the of populations whose members have the potential to interbreed in nature and potential to interbreed in nature and produce viable, fertile offspring but are produce viable, fertile offspring but are unable to produce viable fertile offspring unable to produce viable fertile offspring with members of other populationswith members of other populations
Reproductive IsolationReproductive Isolation
Reproductive isolationReproductive isolation Is the existence of biological factors Is the existence of biological factors
that impede members of two species that impede members of two species from producing viable, fertile hybridsfrom producing viable, fertile hybrids
Is a combination of various Is a combination of various reproductive barriersreproductive barriers
Prezygotic barriersPrezygotic barriers Impede mating between species or hinder Impede mating between species or hinder
the fertilization of ova if members of the fertilization of ova if members of different species attempt to matedifferent species attempt to mate
Postzygotic barriersPostzygotic barriers Often prevent the hybrid zygote from Often prevent the hybrid zygote from
developing into a viable, fertile adultdeveloping into a viable, fertile adult
Prezygotic and postzygotic barriersPrezygotic 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)
Viablefertile
offspring
Reducehybrid
viability
Reducehybridfertility
Hybridbreakdown
Fertilization
Gameticisolation
GAMETIC ISOLATION REDUCED HYBRID VIABILITY
REDUCED HYBRID FERTILITY HYBRID BREAKDOWN
(h) (i)
(j)
(k)
(l)
(m)
(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
Concept 24.2: Concept 24.2: Speciation can Speciation can take place with or take place with or without without geographic geographic separationseparation
Speciation can Speciation can occur in two waysoccur in two ways Allopatric Allopatric
speciationspeciation Sympatric Sympatric
speciationspeciation
Allopatric (“Other Country”) Allopatric (“Other Country”) SpeciationSpeciation
In allopatric speciationIn allopatric speciation Gene flow is interrupted or reduced Gene flow is interrupted or reduced
when a population is divided into two or when a population is divided into two or more geographically isolated more geographically isolated subpopulationssubpopulations
Sympatric (“Same Country”) Sympatric (“Same Country”) SpeciationSpeciation
In sympatric speciationIn sympatric speciation Speciation takes place in geographically Speciation takes place in geographically
overlapping populationsoverlapping populations
An autopolyploidAn autopolyploid Is an individual that has more than two Is an individual that has more than two
chromosome sets, all derived from a chromosome sets, all derived from a single speciessingle 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.
An allopolyploidAn allopolyploid Is a species with multiple sets of Is a species with multiple sets of
chromosomes derived from different chromosomes derived from different speciesspecies
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
Adaptive RadiationAdaptive Radiation Adaptive radiationAdaptive radiation
Is the evolution of diversely adapted Is the evolution of diversely adapted species from a common ancestor upon species from a common ancestor upon introduction to new environmental introduction to new environmental opportunitiesopportunities
Figure 24.11
The punctuated equilibrium model The punctuated equilibrium model Contrasts with a model of gradual Contrasts with a model of gradual
change throughout a species’ existencechange throughout a species’ existence
Figure 24.13
Gradualism model. Species descended from a common ancestor gradually diverge more and more in their morphology as they acquire unique adaptations.
Time
(a) Punctuated equilibrium model. A new species changes most as it buds from a parent species and then changes little for the rest of its existence.
(b)