BIOL 102 General Biology II - Chp 24: The Origin of Species
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Transcript of BIOL 102 General Biology II - Chp 24: The Origin of Species
The Origin of The Origin of SpeciesSpecies
BIOL BIOL 102: 102: General Biology IIGeneral Biology II
Chapter Chapter 2424
Rob Rob SwatskiSwatski Associate Professor Associate Professor of Biologyof Biology
HACCHACC--YorkYork 1
SpeciationSpeciation
Explains how new species originate &
how populations evolve
Microevolution: adaptations that evolve within a
population’s gene pool
Macroevolution: evolutionary change
above the species level
Macroevolution is the cumulative effect of many speciation &
extinction events MicroevolutionMicroevolution 2
MacroevolutionMacroevolution
3
Macroevolution of TechnologyMacroevolution of Technology
4
How is How is Phylogeny Phylogeny
Determined?Determined?
Morphology
Physiology
Biochemistry
DNA sequences
5
Biological Biological Species Species ConceptConcept
A group of populations whose members have
the potential to interbreed in nature …
... & produce viable, fertile offspring
They do not breed successfully with other
populations
Gene flow between populations holds the phenotype together
6
Similarity between two Similarity between two differentdifferent speciesspecies
Eastern meadowlark Western meadowlark
7
Diversity Diversity within within a species a species
The biological species concept The biological species concept is is notnot based on physical similarity based on physical similarity 8
Reproductive Reproductive IsolationIsolation
Biological factors (barriers) that
prevent 2 different species from mating
& producing offspring (hybrids)
Reproductive isolation is classified by whether factors act before or after
fertilization
Prezygotic barriers & Postzygotic barriers
9
Habitat
Isolation Temporal
Isolation
Behavioral
Isolation
Mechanical
Isolation
Gametic
Isolation
Reduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
Individuals of
different species
MATING ATTEMPT FERTILIZATION
VIABLE, FERTILE
OFFSPRING
(a) (c) (e)
(d)
(b)
(g)
(k)
(h) (i)
(j)
(l) (f)
PrezygoticPrezygotic BarriersBarriers
PostzygoticPostzygotic BarriersBarriers
10
PrezygoticPrezygotic BarriersBarriers Block fertilization by:Block fertilization by:
Impeding different species from
attempting to mate
Preventing the successful
completion of mating
Hindering fertilization if
mating is successful
11
Habitat
Isolation
Temporal
Isolation
Behavioral
Isolation
Mechanical
Isolation
Gametic
Isolation
Individuals of
different species
MATING ATTEMPT
FERTILIZATION
(a) (c) (e) (f)
(b)
(g)
(d)
PrezygoticPrezygotic BarriersBarriers
12
Habitat Habitat IsolationIsolation
Two species rarely or never
encounter each other …
… because they occupy different
habitats …
… but are not isolated by
physical barriers
Ex: sticklebacks & garter snake
species 13
St. Lawrence SeawaySt. Lawrence Seaway
14
Water-dwelling garter snake Thamnophis Terrestrial Thamnophis
15
Temporal Temporal IsolationIsolation
Species that breed at different times of the day,
… seasons or years …
… & cannot mix their gametes
Ex: toads & spotted skunks
16
Bufo fowleri
Bufo americanus
17
Eastern spotted skunk (Spilogale putorius)
- mates in late winter
Western spotted skunk (Spilogale gracilis)
- mates in late summer
18
Behavioral Behavioral IsolationIsolation
Behaviors unique to a species are
effective barriers
Courtship rituals
Displays
Vocalizations
19
BlueBlue--Footed Booby Footed Booby Courtship RitualCourtship Ritual
20
Bush Cricket Mating Bush Cricket Mating DisplayDisplay
21
VocalizationVocalization
22
Mechanical Mechanical IsolationIsolation
Morphological differences can
prevent successful mating
Anatomical structures evolve
differently
Body plans are misaligned
23
Genital openings are not in alignment
Bradybaena species with shells spiraling in opposite directions
24
Spider Spider copulatorycopulatory organsorgans
25
GameticGametic IsolationIsolation
Sperm from one species cannot fertilize eggs of another species
Proteins on gamete surfaces cannot bind to
each other
Ex: sea urchins
26
PostzygoticPostzygotic BarriersBarriers Prevent hybrid zygote from developing into a viable,
fertile adult
Reduced hybrid
viability
Reduced hybrid fertility
Hybrid breakdown
27
Reduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
FERTILIZATION
VIABLE, FERTILE
OFFSPRING
(k)
(h) (i)
(j)
(l)
PostzygoticPostzygotic BarriersBarriers
28
Reduced Reduced Hybrid Hybrid
ViabilityViability
Genes of different parent species may
interact & impair hybrid development
May lead to incomplete development of young
Results in weak, frail, & infertile offspring
Ex: salamander (Ensatina) hybrids
29
Reduced Reduced Hybrid Hybrid FertilityFertility
Hybrid development may also be impaired in
other ways
Even if hybrids are vigorous, they may be
sterile
Meiosis in hybrids does not produce normal
gametes
Ex: donkeys & horses have different #’s of
chromosomes 30
Mule Mule (sterile hybrid)(sterile hybrid)
31
Hybrid Hybrid BreakdownBreakdown
Some 1st generation hybrids can be
fertile…
… but, when they mate with another
species (or with either parent
species) …
… offspring of the next generation will be feeble or sterile
Offspring carry too many recessive
alleles 32
Hybrid Rice CultivarsHybrid Rice Cultivars
33
Limitations of Limitations of the Biological the Biological
Species Species ConceptConcept
The biological species concept
cannot be applied to:
Fossils
Asexual organisms
Prokaryotes
Why Not?Why Not?
Why not?Why not? 34
One Species … or Two?One Species … or Two?
35
Grizzly bear (U. arctos)
Polar bear (U. maritimus)
Hybrid “grolar bear” 36
Alternative Definitions of Alternative Definitions of “Species”“Species”
Emphasize the unity within a species, not the separateness between different species
Morphological species concept
Ecological species concept
Phylogenetic species concept
37
Morphological Morphological Species Species ConceptConcept
Defines a species by it’s anatomical
features
Applies to both asexual & sexual
species
… but relies on subjective criteria
Which structures distinguish a
species? 38
39
Ecological Ecological Species Species ConceptConcept
Defines a species by its ecological niche
Also applies to both asexual & sexual
species
Emphasizes the role of disruptive
selection
Ex: barnacle species
40
PhylogeneticPhylogenetic Species Species ConceptConcept
Defines a species as the smallest group of
individuals on a phylogenetic tree
Also applies to both asexual & sexual
species
It can be difficult to determine the
degree of difference required for separate
species
Ex: slime molds 42
SpeciationSpeciation
Allopatric Speciation
Speciation with geographic isolation
(“other country”)
Sympatric speciation
Speciation without geographic isolation
(“same country”) 44
Allopatric speciation Sympatric speciation 45
AllopatricAllopatric SpeciationSpeciation
Gene flow is interrupted or
reduced …
… when a population is divided into
geographically isolated
subpopulations
Ex: habitat fragmentation
46
Habitat Fragmentation Habitat Fragmentation in the Amazon Rainforestin the Amazon Rainforest
47
48
A. harrisi A. leucurus
Harris’s antelope squirrel
(South rim)
White-tailed antelope squirrel
(North rim)
49
Mechanisms of Mechanisms of AllopatricAllopatric SpeciationSpeciation
Mutation Natural
Selection Genetic Drift
50
(a) Under high predation (b) Under low predation
Reproductive isolation as a by-product of selection: Mosquitofish 51
Evidence of Evidence of AllopatricAllopatric SpeciationSpeciation
Regions with many geographic
barriers …
… usually have more species
than regions with fewer barriers
Ex: tropical rain forest frogs
52
A. formosus
Atlantic Ocean
A. nuttingi
Isthmus of PanamaIsthmus of Panama
Pacific Ocean
A. panamensis A. millsae
Allopatric speciation in snapping shrimp
(Alpheus) – sibling species
53
Geographic distance (km)
De
gre
e o
f re
pro
du
ctiv
e is
ola
tio
n
0 0
50 100 150 250 200 300
0.5
1.0
1.5
2.0 Dusky salamandersDusky salamanders
Reproductive isolation increases as the distance between populations increases
54
Sympatric SpeciationSympatric Speciation Occurs in geographically overlapping populations
Polyploidy Habitat
Differentiation Sexual
Selection Hybrid Zones
55
PolyploidyPolyploidy
The presence of extra sets of
chromosomes due to accidents of cell
division
Much more common in plants
than in animals (flatworms, leeches,
salamanders, tree frogs)
Occurs in many important crops:
oats, cotton, potatoes, tobacco, &
wheat
Autopolyploidy & Allopolyploidy
56
57
2n = 6 4n = 12
Failure of cell division after chromosome
duplication gives rise to tetraploid
cells
2n
Gametes produced
are diploid.
4n
Offspring with tetraploid
karyotypes may be viable & fertile
& become new species
AutopolyploidyAutopolyploidy A new species with 2 or more chromosome sets, derived from
one species
58
Species A 2n = 6
Normal gamete
n = 3
Meiotic error
Species B 2n = 4
Unreduced gamete with 4
chromosomes Hybrid with 7
chromosomes
Unreduced gamete with 7
chromosomes
Normal gamete
n = 3
New viable fertile
hybrid species* (allopolyploid)
2n = 10
*The 2n chromosome # of the
new species = the sum of the 2n chromosome #’s of the
parent species
AllopolyploidyAllopolyploidy A new species with multiple sets of chromosomes, derived
from 2 different species
59
Habitat Habitat DifferentiationDifferentiation
Sympatric speciation can also result from the appearance of
new ecological niches
Ex: North American maggot fly
Lives on native hawthorn trees &
more recently introduced apple trees
60
Apples (new habitat) Hawthorns (original habitat)
61
Sexual Sexual SelectionSelection
Can also drive sympatric speciation
Selection for mates of different colors led to
speciation
Ex: cichlids in Lake Victoria
62
63
EXPERIMENTEXPERIMENT
Normal light Monochromatic
orange light
Pundamilia pundamilia
P. nyererei
Females mated with males of both species
Females only mated with males of their own species
64
Hybrid Hybrid ZonesZones
Regions where members of different
species mate & produce hybrids
Provide opportunities to
study factors that cause reproductive
isolation
Ex: swordtails (Xiphophorus)
65
Patterns Patterns Within Hybrid Within Hybrid
ZonesZones
Hybrids can occur in a single band where
adjacent species meet
Hybrids often have reduced fitness compared
with parent species
Hybrid zone distribution can be more complex if
parent species are found in multiple habitats
within the same region
67
68
Fire-bellied toad range
Hybrid zone
Yellow-bellied toad range
Fre
qu
en
cy o
f
B. vari
eg
ata
-sp
ecif
ic a
llele
Yellow-bellied
toad range
Hybrid
zone
Fire-bellied
toad range
Distance from hybrid zone center (km)
40
0.99
0.9
0.5
0.1
0.01
30 20 10 0 10 20
69
Possible Outcomes of Possible Outcomes of Hybrids Over TimeHybrids Over Time
Reproductive barriers become stronger
Reproductive barriers become weaker
Hybrid individuals continue to form
70
Gene flow
Population (5 individuals
are shown)
Barrier to gene flow
Isolated population diverges
Hybrid zone
PossiblePossible outcomes:outcomes:
Reinforcement
OR
OR
Fusion
Stability
Hybrid
71
ReinforcementReinforcement
Occurs when hybrids are less fit than their
parent species
Over time, hybrids gradually stop
forming
Reproductive barriers become
stronger
72
Sympatric male pied flycatcher
Allopatric male pied flycatcher
73
Pied flycatchers
Collared flycatchers
28
24
20
16
12
8
4
0
(none)
Nu
mb
er
of
fem
ale
sN
um
be
r o
f fe
mal
es
Females matingFemales mating with males from:with males from:
Own species
Other species
Sympatric malesSympatric males
Own species
Other species
AllopatricAllopatric malesmales 74
Pundamilia nyererei Pundamilia pundamilia
Pundamilia “turbid water,” hybrid offspring from a location
with turbid water
FusionFusion
Occurs when hybrids have the same fitness as both parent species
There can be significant gene flow
between species
Reproductive barriers weaken
If gene flow is high enough, parent
species can fuse into a single species
75
StabilityStability
Continued production of hybrid individuals
Extensive gene flow from outside the hybrid zone
can overwhelm selection for increased repro isolation inside the
hybrid zone
The resulting 1st or 2nd generation hybrid
offspring are less fit than either parent species
76
SpeciationSpeciation
Can occur slowly or rapidly
Can result from changes in few or many
genes
How long does it take for new species to
form?
How many genes need to differ between
species?
77
Speciation Patterns Can Speciation Patterns Can Be Studied Using:Be Studied Using:
The Fossil Record
Morphological Data
Molecular Data
78
Patterns in Patterns in the Fossil the Fossil
RecordRecord Species may appear
suddenly, persist essentially unchanged for some time, & then apparently disappear
Niles Eldredge & Stephen Jay Gould
coined the term punctuated
equilibrium to describe periods of
apparent stasis punctuated by sudden
change
This contrasts with the gradual change model
79
(a) PunctuatedPunctuated
patternpattern
Time
(b) GradualGradual
patternpattern
80
Speciation Speciation RatesRates
The punctuated pattern in the fossil record & lab
studies suggests that speciation can be rapid
The interval between speciation events can
range from:
4000 years (cichlids) to…
40 million years (some beetles)
81
Rapid Speciation of Rapid Speciation of Helianthus Helianthus anomalusanomalus
82
H. annuus
gamete H. petiolarus
gamete
F1 experimental hybrid
(4 of the 2n = 34
chromosomes are shown)
EXPERIMENT
RESULTS
Chromosome 1
H. anomalus
Chromosome 2
H. anomalus
Experimental hybrid
Experimental hybrid
83
Studying the Studying the Genetics of Genetics of SpeciationSpeciation
Genomics enables researchers to identify
specific genes involved in some cases of speciation
Speciation might require the change of only one
allele …
… or many alleles
84
SingleSingle--Gene SpeciationGene Speciation
85
(a) Typical Mimulus lewisii (b) M. lewisii with an M. cardinalis flower-color allele
A Locus That Influences Pollinator Choice:A Locus That Influences Pollinator Choice: Monkey flowersMonkey flowers
86
(c) Typical Mimulus cardinalis (d) M. cardinalis with an M. lewisii flower-color allele 87
88
CreditsCredits by Rob Swatski, 2013
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