Slajd 1

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11. Patterns of speciation and extinction
The rise and fall of biodiversity Four major mass
extinctions of marine organisms End of Silurian
Devonian, Permian, and Cretaceous) Rise in
diversity during Cambrian, Silurian, Cretaceous,
and Paleogene
The rise and fall of biodiversity 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
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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.
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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
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How do species emerge?
A classical example
Darwin finches, Geospiza spp.)
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
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Speciation is the divergence of genetic structure
between subpopulations until new separate
populations emerge.
Genetic distance
Lineage A
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 spatial
isolationbehavioural isolationtemporal
isolation (separated generations)host switch in
parasites and herbivoresselective habitat choice
Postmating examples are genetic
incompatibilitymorphological incompatibilityearl
y death of hybridssterility
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Speciation due to ecological or spatial or
temporal isolation
Barriers of gene flow or genetical isolation
Allopatric barrier
Peripatric barrier
Ancestral population
Ancestral population
Allopatric speciation
Peripatric speciation
Spatial barrier
Lineage B
Lineage A
Lineage A
Lineage B
Founder effect
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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.
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How fast is speciation?
Are species reproductively independent lineages?
Time to genetic isolation
Time to ecological isolation
Lineage length
Many species do not represent genetically
isolated lineages. However ecological,
morphological or spatial mating barriers exist
It seems that evolutionary speed is not
correlated with generation length and body size
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Adaptation or species selection?
Species selection
Adaptive trend
Time
Time
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.
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Examples of fast evolutionary speed
Minotetrastichus frontalis (ecus)
Mus musculus
Cameraria ohridella
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. 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). Its closest relative was the
now extinct St Kilda House Mouse (Mus musculus
muralis).
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. It is unknown what caused the
rapid spread. Nevertheless it is a good example
how an evolutionary novelty can trigger
dispersion. This dispersion initiated host
switches and lineage divergence of its major
parasite Minotetrastichus frontalis.
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Natura non facit saltus?
Gradualism in Pliocene snails, 10 to 3 Mya.
Species A
Gradual speciation
Species B
Species A
Stasis
Speciation event
Genetic divergence
Species B
Saltatorial speciation
Stasis
Speciation event
Species C
Saltatorial speciation means sudden rapid
evolutionary change that is manifest in genetic
isolation.
Time
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The classic view of speciation
Classical Darwinian selection implies a
continuous (graduate) change in species
characters. The combination with population
genetics gave rise to the neodarwinean synthetic
theory of evolution formulated mainly by Ernst
Mayr and J.B.S. Haldane.
Ernst Mayr, 1904-2005
John B. S. Haldane, 1892-1964

• Phyletic gradualism asserts that
• 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.

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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
• 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.

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Punctuated equilibrium
Speciation
Stasis
Stasis
Evolution is assumed to proceed via fast genetic
transitions within an peripatric speciation
framework.
Speciation
Stasis
Genetic distance
Speciation
Subspeciation
Stasis
Time
Mean thorax width of Trilobite species
The evolution of man is a good example of
punctuated equilibrium.
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Does evolution need hopeful monsters? Or
evolution above the species level
Classical Darwinian theory assumes character
evolution to be a gradual process. 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?
Richard Goldschmidt,1878-1958
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.
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The history of whales Gradualism or
saltationism?
The history of birds Gradualism or saltationism?
65 mya
Paleocene
Jura
150mya
First feathers
Sinosauro- pteryx prima
Eocene
50 mya
Ambulocetans natans
46 mya
Caudipteryx zoui
Rhodocetus kasrani
40 mya
Protarchaeo-pteryx robusta
135 mya
Dorudon atrox
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Evolutionary trends and major questions
Major evolutionary trends
Evolutionary constraints

• Rising number of genes across clades?
• Rising morphological complexity across clades?
• Rising hierarchical organization?
• Rising physiological and ecological flexibility?
• Rising efficiacy in design?
• Rising evolvability (the ability to cope with
  changing environmental conditions)?
• Decreasing evolvability due to trends for
  specialization?
• Rising complexity of ecological interactions?

• What made vertebrates prone to evolve large
  brains?
• Why did insects never get large?
• Why did plants never evolve nerves and muscles?
• Why did Dinosaurs not become small?
• Why did marine taxa stop evolving since the
  Cambrian?
• Why did major taxa (phyla) only evolve in the
  late Proterozoic?
• Did life appear only once?

Discuss these questions using the many internet
sources!
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Extinctions
Marine taxa
Trade off between extinction and speciation
The background extinction rate e(t) of marine
taxa decreased!
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Trade off between extinctions and speciations
Extinction and origination rates are
connected. Peaks in speciation of marine taxa
occurred often after mass extinctions.
Mass extinctions might also change ecological
dominance. Bivalvia raised after the mass
extinction of the ecologically similar
Brachiopoda.
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Mass extinctions are not equally distributed
among taxa. Advanced species that are
physiologically more buffered against
environmental changes increased in frequency
after mass extinctions
Motile species were often less affected than
sessile species
Predator species richness increased after mass
extinctions
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Adaptation to herbivory and promiscuity might
cause high rates of speciation
Change in feeding style
Cucujoidea lt 10000 species
Curculionoidea gt 200000 species
Trichoptera lt 10000 species
Lepidoptera gt 300000 species
Herbivory
Herbivory
Predators
Predators
Detritivorous
Change in mating system
Manucodes 5 species
Birds of paradise 33 species
Hummingbirds 319 species
Swifts103 species
Promiscuity
Promiscuity
Pair bonds
Pair bonds
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The interplay between extinction and origination
Correlations between actual diversity and
speciation r(D-DS) and extinction rates r(D-DE)
(mid Jurassic to Neogene) show that high
diversities were correlated with high extinction
rates but not with high speciation rates. This
points to a density dependent effect in
speciation.
The equilibrium number of species is then
Hence, the realized number of species is always
lower than the maximum possible
number. Ecological systems cannot be saturated
with species.
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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)
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Extinction rates seem to be pylogenetically
clustered
Extinction rates were phylogenetically clustered
in time
Extinction rates of mesozoic Bivalvia were stable
in time
From Roy et al. 2009)
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The Red Queen hypothesis
Leigh M. Van Valen 1935-
Extinction rates (probabilities) are roughly
constant through time. One explanation for this
is the Red Queen hypothesis (after Lewis
Carrolls 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.
Survival times for extinct genera of Echinoidea
(sea urchins).
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Todays reading
Speciation http//en.wikipedia.org/wiki/Speciatio
n Observed instances of speciation
http//www.talkorigins.org/faqs/faq-speciation.htm
l The origin of species http//bill.srnr.arizona.
edu/classes/182/Lecture202007-03.htm Punctuated
equilibrium http//en.wikipedia.org/wiki/Punctuat
ed_equilibrium Punctuated equilibrium
http//www.mun.ca/biology/scarr/2900_Fossils.htm