Speciation and Macroevolution
• Speciation
• Divergent Evolution
• Convergent Evolution
Evolutionary change of a
species over time
Creation of new groupspeciation  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
Isolated
population
diverges.
Gene flow
Population
Barrier to
gene flow
Figure 24.13-2
Mating doesn’t occur
Gametes don’t unite
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
Experiment
Initial population
of fruit flies
(Drosophila
pseudoobscura)
Some flies raised on
starch medium
Some flies raised on
maltose medium
Mating experiments
after 40 generations
Results
Female
9
8
20
Number of matings
in experimental group
Starch
population 2
Starch
population 1
Starch
22
Starch
population 1
18
15
Starch
population 2
Maltose
Male
Starch
Maltose
Female
Male
• Reproductive barriers can
develop when laboratory
populations are
experimentally isolated and
subjected to different
environmental conditions
12
15
Number of matings
in control group
Figure 24.7
(a) Under high predation
(b) Under low predation
Females from each pop show strong preference for their own body
shape in mate selection
Figure
24.6
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
I love a man
with a red
nose
Orange noses
are dreamy
Figure 24.11
Experiment
Normal light
P. pundamilia
P. nyererei
Monochromatic
orange light
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
Cell
division
error
• An autopolyploid is an
individual with more than
two chromosome sets,
derived from a single
species
2n = 6
Tetraploid cell
4n
Meiosis
2n
2n
Gametes produced
by tetraploids
New species
(4n)
Autopolyploid speciation
Figure 24.UN02
• An allopolyploid is a species with
multiple sets of chromosomes
derived from different species
Species A
2n = 6
Normal gamete
n=3
Species B
2n = 4
Normal gamete
n=2
Sterile hybrid with
5 chromosomes
Mitotic or meiotic error
doubles the chromosome
number.
New species:
viable, fertile hybrid
(allopolyploid)
2n = 10
Figure 24.9-3
Figure 24.10
T. dubius
(12)
Hybrid species:
T. miscellus
(24)
T. pratensis
(12)
Hybrid species:
T. mirus
(24)
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
(a) Punctuated model
Time
(b) Gradual model
Figure 24.16
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
68x more hummmingbrid visits
than wild-type M. lewisii
Preferred by
bumblebees
(a) Mimulus lewisii
(b) M. lewisii with
M. cardinalis allele
74x more bumblebee visits
than wild-type M. cardinalis
Preferred by
hummingbirds
(c) Mimulus cardinalis
(d) M. cardinalis with
M. lewisii allele
Figure 24.19
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