Transcript Selection and adaptation

11. Patterns of speciation and extinction
z
800
N u m b e r o f fa m ilie s
900
700
The rise and fall of biodiversity
M as s e xtinc tio ns
Four major mass extinctions of marine
organisms:
600
500
End of Silurian Devonian, Permian, and
Cretaceous)
400
300
200
Rise in diversity during Cambrian, Silurian,
Cretaceous, and Paleogene
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Kr
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Pa N
2500
Eliminating all groups known only from a
single stage (5-6 mya):
Rise in diversity during Cambrian, and
Ordovicium and in the Paleogene
Decline of longer lasting taxa from
Ordovicium to Triassic
M as s e xtinc tio ns
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N u m b e r o f fa m ilie s
The rise and fall of biodiversity
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1000
500
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What is a species in the evolutionary context?
Corvus corax
Corvus corone
Corvus frugilegus
The biological species concept states that species are actually or potentially interbreeding
natural populations that are genetically isolated from others
The evolutionary species concept states that species are ancestor – descendent lineages of
organisms that have their own evolutionary fate.
The phylogenetic species concept states that a species is the smallest monophyletic group
of organisms of common ancestry (a lineage from one node to another).
The genetic species concept states that a species is a genetically sufficiently distinct group
of organisms as identified by a genetic fingerprint.
The ecological species concept states that a species is a group of organisms (population)
that are ecologically distinct from other groups.
The heuristic species concept states that a species is a group of organisms that are
practically clustered together for the aims of a certain study.
Does any species concept fit?
Thelytokous waps
Morphologically divergent races
Dog races
Meteorus pulchricornis
from New Zealand
Heliconius butterflies
Salmonella typhi
Presexual species
Genetical fingerprint „species”
How do species emerge?
A classical example
1. Large cactus finch (Geospiza conirostris)
2. Large ground finch (Geospiza magnirostris)
3. Medium ground finch (Geospiza fortis)
4. Cactus finch (Geospiza scandens)
5. Sharp-beaked ground finch (Geospiza difficilis)
6. Small ground finch (Geospiza fuliginosa)
7. Woodpecker finch (Cactospiza pallida)
8. Vegetarian tree finch (Platyspiza crassirostris)
9. Medium tree finch (Camarhynchus pauper)
10. Large tree finch (Camarhynchus psittacula)
11. Small tree finch (Camarhynchus parvulus)
12. Warbler finch (Certhidia olivacea)
13. Mangrove finch (Cactospiza heliobates
Darwin finches, Geospiza spp.)
Genetic distance
Lineage A
Speciation is the divergence of genetic structure
between subpopulations until new separate populations
emerge.
Lineage B
Any mechanism that promotes the emergence of
sublineages is therefore a potential speciation mechanism
Basal population
Divergence can be triggered by premating and postmating mechanisms:
Premating mechanisms are those that keep populations isolated before mating occurs.
Postmating mechanisms prevent hybrids to develop or breed.
Premating examples are:
Postmating examples are:
spatial isolation
behavioural isolation
temporal isolation (separated generations)
host switch in parasites and herbivores
selective habitat choice
genetic incompatibility
morphological incompatibility
early death of hybrids
sterility
Speciation due to ecological or spatial or temporal isolation
Barriers of gene flow or genetic isolation
Allopatric barrier
Peripatric barrier
Ancestral population
Ancestral population
Allopatric speciation
Lineage
A
Spatial
barrier
Peripatric speciation
Lineage
B
Lineage
A
Lineage
B
Founder effect
Barriers of gene flow or genetic isolation
Sympatric lineage emergence
Parapatric lineage emergence
Ancestral population
Ancestral population
Sympatric speciation
Parapatric speciation
Genetic differences within the same
geographical region result in genetic
isolation and lineage divergence.
Differential selection pressures cause
lineage divergence even within narrow
spatial ranges.
How fast is speciation?
Time to
genetic
isolation
Are species reproductively independent
lineages?
S e e d p la nts
Time to
ecological
isolation
Lineage
length
M a m m a ls
Inse cts
F e rns
G e n e tic is o la tio n
T axo n
F ro g s
F ishe s
N .A . so ng b ird s
B ird s
D ro so p hila
L in e a g e le n g th
A ntho zo a
B iva lvia
A m p hib ia
H o rse s
C ichlid s
0
H a w a iia n D ro so p hila
0 .2
0 .4
0 .6
0 .8
1
P ro p o rtio n o f taxo no m ic s p e c ie s that
M a m m a ls
re p re s e nt re p ro d uc tive ly ind e p e nd e nt
A ng io sp e rm s
Tre e s
0
2
4
6
8
Mya
10 12 14
It seems that evolutionary speed is not correlated
with generation length
and body size
line ag e s
Many ‘species’ do not represent genetically
isolated lineages. However ecological,
morphological or spatial mating barriers
exist
Examples of fast evolutionary speed
Minotetrastichus
frontalis (=ecus)
Cameraria ohridella
The Aesculus miner C. ohridella was first
described in 1984 in Albania as a rare new
species.
Since then it colonized whole Europe and
became a dominant mining species on Aesculus
hippocastanus.
Mus musculus
The Faroer Island house mouse originated
from the Western European House Mouse
(Mus domesticus).
During 250 years of colonization it has
evolved three distinct isolated island
populations.
Nevertheless it is a good example how an
evolutionary novelty can trigger dispersion.
The Nólsoy House Mouse is a sub-species
called (Mus musculus faeroensis) and the
Mykines House Mouse is also a sub-species
called (Mus musculus mykinessiensis).
This dispersion initiated host switches and
lineage divergence of its major parasite
Minotetrastichus frontalis.
Its closest relative was the now extinct St
Kilda House Mouse (Mus musculus muralis).
It is unknown what caused the rapid spread.
The classic view of speciation
Classical Darwinian selection
implies a continuous
(graduate) change in species
characters.
Ernst Mayr, 1904-2005
Phyletic gradualism asserts that
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John B. S. Haldane,
1892-1964
The combination with
population genetics gave rise
to the neodarwinean
synthetic theory of
evolution formulated mainly
by Ernst Mayr and J.B.S.
Haldane.
Species arise by the transformation of an ancestral population into its modified descendants.
The transformation is even and slow.
The transformation involves large numbers, usually the entire ancestral population.
The transformation occurs over all or a large part of the ancestral species' geographic range
This implies that
• Ideally, the fossil record for the origin of a new species should consist of a long sequence of
continuous, insensibly graded intermediate forms linking ancestor and descendant.
• Morphological breaks in a postulated phyletic sequence are due to imperfections in the
geological record.
Natura non facit saltus?
Gradualism in Pliocene snails, 10 to 3 Mya.
Species A
Genetic divergence
Gradual speciation
Species B
Stasis
Species A
Speciation event
Stasis
Species B
Saltatorial speciation
Species C
Saltatorial speciation
means sudden rapid
evolutionary change that
is manifest in genetic
isolation.
Speciation event
Time
Tempo and mode of evolution reconsidered
Stephen Jay
Gould, 1941-2002
Niles Eldredge
1943-
The theory of punctuated equilibrium of Niles Eldredge and Stephen Jay Gould states that
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The fossil record is relatively complete.
Most speciation occurs via peripatric speciation.
Widespread species usually change slowly, if at all, during their time of existence.
Daughter species usually develop in a geographically limited region.
Daughter species usually develop in a stratigraphically limited extent.
Sampling of the fossil record will reveal a pattern of most species in stasis, with abrupt
appearance of newly derived species being a consequence of ecological succession and
dispersion.
Adaptive change in lineages occurs mostly during periods of speciation.
Trends in adaptation occur mostly through the mechanism of species selection.
Adaptation or species selection?
Adaptive trend
Time
Time
Species selection
Morphological
divergence
Morphological
divergence
Species selection means that evolution
proceeds via differential extinction of species
with certain characteristic features.
Adaptive trends imply differential speciation
rates of better adapted lineages.
Genetic distance
Punctuated equilibrium
Speciation
Stasis
Stasis
Stasis
Speciation
Evolution is assumed to proceed via fast
genetic transitions within an peripatric
speciation framework.
Speciation
Stasis Subspeciation
Time
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C lad o g e ne s is
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T h o ra x w id th
S tas is
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S tas is
110
C lad o g e ne s is
100
Time before present
0
Homo sapiens
-1000000
-2000000
Homo erectus
Homo habilis/ergaster
-3000000
-4000000
Australopithecus
C ladCladogenesis
o g e ne s is
S tas is
Mean thorax width
of Trilobite species
90
-5000000
0
500
1000
1500
2000
Cranial capacity
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-1 8 0 0
-1 6 0 0
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C o re d e p th [c m ]
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The evolution of man is a good example of
punctuated equilibrium.
Does evolution need hopeful monsters? Or evolution above the species level
Classical Darwinian theory assumes
character evolution to be a gradual process.
Richard
Goldschmidt,
1878-1958
However higher taxa are of often
distinguished without any intermediate
fossils (fossil gaps).
Did major evolutionary branches evolved
very fast or is our fossil record too
incomplete?
Goldschmidt assumed that major evolutionary transitions are caused by mutations in
regulatory genes giving rise to major morphological changes.
Most of these highly altered creatures have no chance to survive, but few succeed and
are ‘hopeful monsters’ that are ancestors of new higher taxa.
Punctuated equilibrium is a modern form of this saltationism.
150
mya
Paleocene
65
mya
The history of whales: Gradualism or
saltationism?
First
feathers
Sinosauropteryx prima
Eocene
40
mya
Ambulocetans
natans
Jura
50
mya
46
mya
The history of birds: Gradualism or
saltationism?
Caudipteryx
zoui
Rhodocetus
kasrani
Dorudon atrox
135
mya
Protarchaeopteryx robusta
The rise of major lineages
Cryogenian
Ediacaran
850-630
630-540
Sponges
Mass
extinction
Rangeomorpha
Cambrian
540-490
Ordovician
490-440
Silurian
440-410
Chordata
Erniettomorpha Echinodermata
Cnidaria
Chelicerata
Mollusca
Trilobites
Annelida
„Crustacea”
Basal
arthropods
„Myriapoda”
Cephalopoda
Insects
Pisces
Basic members of
nearly all major phyla
Very probably all animal phyla (except sponges) appeared during the Ediacarian and
Cambrian periods. About 35 of the lineages survived.
Later, only new classes appeared.
By the end of the carbon all extant classes were already present.
Evolution and development (EvoDevo)
August Weismann
(1834-1914)
The soma - germ line
distinction
makes it impossible to
transmit acquired characters
to the next generation
Ernst Haeckel
(1834-1919)
Theory of recapitulation
The ontogeny of
advanced species
recapitulates respective
stages in ancestral
forms.
In fact, only basic genetic
programs are conserved
and modifications at all
stages of ontogenesis
appear.
Haeckel’s rule is only a
crude approximation.
EvoDevo and the constraints
Steps of gene switching
Segment
differentiation
organ
development
Probability
of lethal
mutations
for higher
advanced
organisms
Segment
differentiation
Supply and neural
networks
Adult
Tunicate
Vertebrate
embryo
Class specific
body plans
Tunicate
larva
New classes arise from
free living larval stages,
for instance by Neoteny
HOX genes
Genes for basic
body shape and
cell types
Genes for cell
division and
adhesion
Phylum specific body plans
Seastar
Gastrula
New phyla arise from
free living gastrula
stages
Common to all extant
animals
Zygote
The evolution of ecological complexity
Chains including parasitoid levels
Phagocytic
Eukaryotes
By the end of the Cambrium
marine food chains nearly reached
today’s complexity
Complex
All major types of
terrestrial
marine animals
arthropod
based food
First filterchains
feeding
Porifera
First land living
arthropod
predators
First land living
Cyanobacteria
By the end of the Cambrium all major marine and
freshwater ecological niches were occupied, leaving
no room for additional aquatic born phyla.
First land living
Eukaryotes
Terrestrial food chains still appear
to increase in complexity
zs f
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E x tin c tio n s o f fa m ilie s
Extinctions
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18
Marine taxa
Mass
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e x tin c tio n s
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2
R = 0 .2 1
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p (t) < 0 .0 0 0 1
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Trade off between extinction and speciation
dS
dt
 c( t )S  e( t )S  (c  e)S  S t  S 0 e
[ c ( t )  e ( t )] t
The background extinction rate e(t) of marine taxa decreased!
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S ta n d . n u m b e rs o f fa m ilie s
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M a ss e xtinctio ns m ig ht b e fo llo w e d b y hig h
O rig in a tio n ra te o f g e n e ra
z
Trade off between extinctions and speciations
o rig ina tio n ra te s
Extinction and origination
rates are connected.
Peaks in speciation of
marine taxa occurred often
after mass extinctions.
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E x tin c tio n s o f fa m ilie s
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Mass
e x tin c tio n
500
B iv a lv ia
Mass extinctions might also
change ecological dominance.
400
300
Bivalvia raised after the mass
extinction of the ecologically
similar Brachiopoda.
200
B ra c h io p o d a
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B u ffe re d
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Mass extinctions are not equally
distributed among taxa.
s p e c ie s
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0 .6
Advanced species that are physiologically
more buffered against environmental
changes increased in frequency after
mass extinctions
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Mass
U n b u ffe re d
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e x tin c tio n
s p e c ie s
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P ro p o rtio n o f m a rin e g e n e ra
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M o tile
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s p e c ie s
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0 .7
Motile species were often less affected
than sessile species
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S e s s ile
Mass
s p e c ie s
e x tin c tio n
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P ro p o rtio n o f m a rin e g e n e ra
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P re y
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Predator species richness increased after
mass extinctions
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Mass
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e x tin c tio n
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P re d a to rs
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Species richness and taxon age
Species richness increases with taxon age.
Speciation rates l are independent of species
richness but decrease with taxon age.
Younger taxa have higher speciation rates l.
Total species richness is also determined by
species survival rates.
Insecta and Vertebrata
Chordata
Arthropoda
Mollusca
Data from Mc Peek, Brown (2007)
The Red Queen hypothesis
Positive age
dependent rate of
extinction
1000
Constant rate of
extinction
100
Negative age
dependent rate of
extinction
10
Leigh M. Van Valen
1935- 2010
1
200
400
Time (m ya)
z
0
N u m b e r o f g e n e ra z
Number of surviving taxa
10000
1000
y = 633e
600
-0.038x
100
10
1
0
50
100
150
200
S urvival tim e [m ya]
Survival times for extinct genera of
Echinoidea (sea urchins).
Extinction rates (probabilities) are
roughly constant through time.
One explanation for this is the Red
Queen hypothesis (after Lewis
Carroll’s Through the Looking Glass).
Each species has to run as far as
possible (to evolve continuously) only
to stay in the same place.
Its competitors, predators and
parasites also evolve continuously.
Under these circumstances extinction
probabilities will remain roughly
constant in time.
Today’s reading:
Speciation: http://en.wikipedia.org/wiki/Speciation
Observed instances of speciation: http://www.talkorigins.org/faqs/faq-speciation.html
The origin of species: http://bill.srnr.arizona.edu/classes/182/Lecture%202007-03.htm
Punctuated equilibrium: http://en.wikipedia.org/wiki/Punctuated_equilibrium
Punctuated equilibrium: http://www.mun.ca/biology/scarr/2900_Fossils.htm