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Speciation and Macroevolution• Speciation• Divergent Evolution• Convergent Evolution
Evolutionary change of a species over time
Creation of new groupspeciation diversity of living things.
Speciation & Macroevolution
• Microevolution = evolution on small scale• changes in allele frequency in a population over time
• Speciation = formation of new species• Bridges micro and macro-evolution
• Macroevolution = large scale evolution• broad patterns of evolutionary change; species formation and larger
What is a species?
• biological species concept: • A group of individuals (i.e., multiple pops.) that have the potential to interbreed in
nature and produce viable, fertile offspring.• Based on reproductive compatibility and isolation• Weakness of this def:
• Other species definitions:• Morphological species concept: based on structure• Ecological species concept: based on niche (i.e., role in ecosystem)• Phylogenetic species concept: based on common ancestor (evolutionary relationship)• More…..
Reproductive Isolation• Reproductive isolation : inability to mate and produce viable, fertile
offspring• Classification/Types of Isolation:• Prezygotic Barriers• Pre-mating attempt• Post-mating attempt
• Post-zygotic Barriers
Figure 24.13-2
Gene flow
Population Barrier togene flow
Isolatedpopulationdiverges.
Gametes don’t uniteMating doesn’t occur
Offspring doesn’t survive or can’t perpetuate species
• Prezygotic barriers block fertilization from occurring by• Impeding different species from attempting to mate• Preventing the successful completion of mating• Hindering fertilization if mating is successful
• Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult• Reduced hybrid viability• Reduced hybrid fertility• Hybrid breakdown
Two forms of Speciation:• Allopatric: speciation with
geographic separation• Non-overlapping populations• “Barrier” is relative to dispersal
ability of organism• Even if contact is restored,
interbreeding is prevented
• Sympatric: speciation within the same geographic location/area• Overlapping
Allopatric Speciation: A tale of two fuzzy animals
Figure 24.7
Experiment
Results
Some flies raised on starch medium
Initial populationof fruit flies(Drosophila
pseudoobscura)
Mating experimentsafter 40 generations
Some flies raised on maltose medium
FemaleStarch
population 1Starch
population 2
Female
Starch Maltose
9
208
22
Star
chM
alto
seM
ale
Mal
eSt
arch
popu
latio
n 1
Star
chpo
pula
tion
2
18
12 15
15
Number of matingsin control group
Number of matingsin experimental group
• Reproductive barriers can develop when laboratory populations are experimentally isolated and subjected to different environmental conditions
Figure 24.6
(a) Under high predation (b) Under low predation
Females from each pop show strong preference for their own body shape in mate selection
Sympatric Speciation
• Mechanisms for sympatric speciation• Habitat differentiation• Sexual selection• Polyploidy
A “tale” of two squirrels
Sexual Selection• Preference for specific traits (e.g., morphological or behavioral) by
subset of females can lead to reproductive isolation.• E.g. Sexual selection for mates of different colors has likely contributed to
speciation in cichlid fish in Lake Victoria
Orange noses are dreamy
I love a man with a red
nose
Figure 24.11
Normal lightMonochromatic
orange light
P. pundamilia
P. nyererei
Experiment
Polyploidy
• Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division• Polyploidy can produce new biological species in sympatry within a
single generation• Autopolyploid: from a single species• Allopolyploid: from hybrids of two species
• An autopolyploid is an individual with more than two chromosome sets, derived from a single species
Celldivisionerror
Tetraploid cell4n
2n = 6
2n
2n
Meiosis
New species(4n)Gametes produced
by tetraploids
Autopolyploid speciation Figure 24.UN02
• An allopolyploid is a species with multiple sets of chromosomes derived from different species
Species A2n = 6
Normal gameten = 3
Normal gameten = 2
Species B2n = 4
Sterile hybrid with5 chromosomes
Mitotic or meiotic errordoubles the chromosomenumber.
New species:viable, fertile hybrid(allopolyploid)2n = 10
Figure 24.9-3
Figure 24.10T. dubius(12)
Hybrid species:T. miscellus(24)
Hybrid species:T. mirus(24)
T. pratensis(12)
T. porrifolius(12)
Rate of speciation
• It can happen quickly (punctuated equilibrium model)• It can happen slowly (gradualism)• The interval between speciation events can range from 4,000 years (some
cichlids) to 40 million years (some beetles), with an average of 6.5 million years
Figure 24.16
(a) Punctuated model
(b) Gradual model
Time
Studying the Genetics of Speciation• How many genes change when a new species forms?• As few as a single gene or in other cases many genes• For example, in Japanese Euhadra snails, the direction of shell spiral affects mating
and is controlled by a single gene
• In monkey flowers (Mimulus), two loci affect flower color, which influences pollinator preference• Pollination that is dominated by either hummingbirds or bees can lead to reproductive
isolation of the flowers
• In other organisms, speciation can be influenced by larger numbers of genes and gene interactions
Figure 24.19
(a) Mimulus lewisii M. lewisii withM. cardinalis allele
(b)
M. cardinalis withM. lewisii allele
(c) Mimulus cardinalis (d)
Preferred by hummingbirds
Preferred by bumblebees
68x more hummmingbrid visits than wild-type M. lewisii
74x more bumblebee visits than wild-type M. cardinalis
Convergent Evolution• When similar selective forces cause similarities (similar traits) in
unrelated species• E.g., body shape of aquatic organism (shark and dolfins) • Similar structure of desert plants cacti & euphorbs
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