Ch 24: The Origin of Species
Macroevolution: the origin of new taxonomic groups
Speciation: the origin of
new species
1- Anagenesis (phyletic evolution):
accumulation of heritable changes
2- Cladogenesis (branching evolution):
budding of new species from a parent species
that continues to exist (basis of biological
diversity)
What is a species?
• Biological species concept
(Mayr): a population or group
of populations whose members
have the potential to interbreed and
produce viable, fertile offspring
(genetic exchange is possible and
that is genetically isolated from
other populations)
Reproductive Barriers
Pre-zygotic
Reproductive Isolation (isolation of gene pools)
Prezygotic barriers: impede
mating between species or
hinder the fertilization of the
ova
Examples:
• Habitat (snakes; water/terrestrial)
• Behavioral (fireflies; mate signaling)
• Temporal (salmon; seasonal mating)
• Mechanical (flowers; pollination
anatomy)
• Gametic (frogs; egg coat receptors)
Reproductive Barriers
Pre-zygotic
Habitat isolation
Geographic isolation
Habitat isolation
Geographic isolation
Eurasian spoonbill
North America
Madagascar
Central America
Roseate spoonbill
1
Reproductive Barriers
Pre-zygotic
Reproductive Barriers
Pre-zygotic
Habitat isolation
Geographic isolation
Ecological isolation
Habitat isolation
Geographic isolation
Ecological isolation
Behavioral (mate choice) isolation
Rhagoletis pomonella
Hawthorns or apples
for oviposition
Galapagos
Islands
Red-footed booby
Satin Bowerbirds & their
bowers
Blue-footed boobies
Australia
Tooth-billed Catbird’s
leaf display
Reproductive Barriers
Dog-day
(17 year)
Pre-zygotic
Habitat isolation
Geographic isolation
Ecological isolation
Behavioral (mate choice) isolation
Temporal isolation
Periodical
(12 year)
2
Reproductive Barriers
Pre-zygotic
Habitat isolation
Geographic isolation
Ecological isolation
Behavioral (mate choice) isolation
Temporal isolation
Mechanical isolation
C. wapleri
Reproductive Barriers
Pre-zygotic
Thompson Creek, W. Feliciana Parish
head
acrosome
tail
Habitat isolation
Geographic isolation
Ecological isolation
Behavioral (mate choice) isolation
Temporal isolation
Mechanical isolation
Gametic isolation
midpiece
ovum
Reproductive Isolation
Postzygotic barriers: fertilization
occurs, but the hybrid zygote
does not develop into a viable,
fertile adult
Examples:
• Reduced hybrid viability (frogs; zygotes fail to
develop or reach sexual maturity)
• Reduced hybrid fertility (mule; horse x
donkey; cannot backbreed)
• Hybrid breakdown (cotton; 2nd generation
hybrids are sterile)
3
Modes of speciation
♀
(based on how gene flow is interrupted)
• Allopatric:
x
populations segregated by a
geographical barrier; can
result in adaptive radiation
(island species)
=
♂
• Sympatric:
sterile
Allopatric speciation
reproductively isolated
subpopulation in the midst of
its parent population (change
in genome); polyploidy in
plants; cichlid fishes
Sympatric speciation
Divergence occurs in geographic isolation
Divergence occurs despite lack of geographic isolation
Allopatric vs. sympatric speciation
Adaptive Radiation
Figure
24.5
One species gives rise to many others in a
geologically short period of time
E.g., Darwin’s
finches
Islands are
good places to
find adaptive
radiations
4
Adaptive Radiation
Punctuated equilibria
E.g., Hawaiian silverswords
• Tempo of speciation:
gradual vs. divergence in
rapid bursts; Niles Eldredge
and Stephen Jay Gould
(1972); helped explain the
non-gradual appearance of
species in the fossil record
Figure 24.12
Evolution is not “goal oriented”
Evolution is a genetic response to the interaction
between the individuals of a population and their
current environment (which includes other
individuals)
Natural selection can only act on the phenotypic
variation present, and selection can only cause
evolutionary change if phenotypic variation
results (at least in part) from genetic variation
Evolution is not “goal oriented”
Therefore, even if female tigers in a population
would prefer blue males, blue tigers will never
evolve if the population lacks variation that
includes blue fur
YES! But he
exists only
in my dreams.
He’s not blue,
but he’s better
than nothing!
5