11. Patterns of speciation and extinction
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Mass extinctions
E
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
What is a species in the evolutionary context?
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.
Corvus corax Corvus corone Corvus frugilegus
Does any species concept fit?
Meteorus pulchricornis from New Zealand
Salmonella typhiHeliconius butterflies
Dog races
Thelytokous waps
Presexual species
Morphologically divergent races
Genetical fingerprint „species”
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
Speciation is the divergence of genetic structure between subpopulations until new separate populations
emerge.
Any mechanism that promotes the emergence of sublineages is therefore a potential speciation mechanism
Premating examples are:
spatial isolationbehavioural isolationtemporal isolation (separated generations)host switch in parasites and herbivoresselective habitat choice
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.
Postmating examples are:
genetic incompatibilitymorphological incompatibilityearly death of hybridssterility
Basal population
Lineage A Lineage B
Genetic distance
Speciation due to ecological or spatial or temporal isolation
Barriers of gene flow or genetic isolation
Allopatric barrier
Ancestral population
Spatial barrier
Lineage A
Lineage B
Peripatric barrier
Ancestral population
Lineage A
Lineage B
Founder effect
Allopatric speciation Peripatric speciation
Sympatric lineage emergence
Ancestral population
Genetic differences within the same geographical region result in genetic
isolation and lineage divergence.
Parapatric lineage emergence
Differential selection pressures cause lineage divergence even within narrow
spatial ranges.
Ancestral population
Barriers of gene flow or genetic isolation
Sympatric speciation Parapatric speciation
How fast is speciation?
Lineage length
Time to genetic
isolation
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Angiosperms
Mammals
Hawaiian Drosophila
Cichlids
Horses
Frogs
Lineage length
Genetic isolation
N.A. songbirds
Drosophila
Mya
Bivalvia
Trees
It seems that evolutionary speed is not correlated with generation length
and body size
Are species reproductively independent lineages?
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Amphibia
Anthozoa
Birds
Fishes
Ferns
Insects
Mammals
Seed plants
Taxon
Proportion of taxonomic species that represent reproductively independent
lineages
Many ‘species’ do not represent genetically isolated lineages. However ecological, morphological or spatial mating barriers
exist
Time to ecological
isolation
Examples of fast evolutionary speed
Cameraria ohridella
Minotetrastichus frontalis (=ecus)
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.
Mus musculus
The classic view of speciation
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
rangeThis 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.
Ernst Mayr, 1904-2005
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.
John B. S. Haldane, 1892-1964
Natura non facit saltus?
Species A
Species B
Species A
Species B
Species C
Time
Gen
etic
div
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nce
Speciation event
Speciation event
Gradual speciation
Saltatorial speciation
Gradualism in Pliocene snails, 10 to 3 Mya.
Saltatorial speciation means sudden rapid
evolutionary change that is manifest in genetic
isolation.
Stasis
Stasis
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.
Tempo and mode of evolution reconsidered
Stephen Jay Gould, 1941-2002
Niles Eldredge 1943-
Adaptation or species selection?
Morphological divergence
Tim
eSpecies selection
Morphological divergence
Tim
e
Adaptive trend
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.
Time
Gen
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dis
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Speciation
Speciation
Speciation
Subspeciation
Stasis
Stasis
Stasis
Stasis
Evolution is assumed to proceed via fast genetic transitions within an peripatric
speciation framework.
Punctuated equilibrium
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Stasis
Stasis
Stasis
Cladogenesis
Cladogenesis
Cladogenesis
Mean thorax width of Trilobite species
The evolution of man is a good example of punctuated equilibrium.
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Tim
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Cranial capacity
Australopithecus
Homo habilis/ergaster
Homo erectus
Homo sapiens
Does evolution need hopeful monsters? Or evolution above the species level
Richard Goldschmidt,1878-1958
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?
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.
Ambulocetans natans
Dorudon atroxEoc
ene
50 mya
40 mya
Pal
eoce
ne65
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Rhodocetus kasrani
The history of whales: Gradualism or saltationism?
46 mya
The history of birds: Gradualism or saltationism?
Protarchaeo-pteryx robusta Ju
ra
150mya
135 mya
Caudipteryx zoui
Sinosauro-pteryx prima
First feathers
The rise of major lineages
Cryogenian
850-630
Ediacaran
630-540
Cambrian
540-490
Mass extinction
Ordovician490-440
Silurian440-410
Sponges Rangeomorpha
Erniettomorpha
Cnidaria
Mollusca
Annelida
Basal arthropods
Basic members of nearly all major phyla
Chordata
Echinodermata
Cephalopoda
Pisces
Chelicerata
Trilobites
„Crustacea”
„Myriapoda”
Insects
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
Genes for cell division and
adhesion
HOX genesGenes for basic body shape and
cell types
Segment differentiation
Supply and neural networks
Segment differentiation
organ development
Common to all extant animals
Phylum specific body plans
Class specific body plans
Steps of gene switching
Probability of lethal
mutationsfor higher advanced
organisms
Seastar Gastrula
Zygote
New phyla arise from free living gastrula stages
New classes arise from free living larval stages, for instance by Neoteny
Tunicate larva
Vertebrate embryo
Adult Tunicate
Phagocytic Eukaryotes
First filter-feeding Porifera
All major types of marine animals
First land living Cyanobacteria
First land living Eukaryotes
First land living arthropod predators
Complex terrestrial arthropod
based food chains
Chains including parasitoid levels
The evolution of ecological complexity
By the end of the Cambrium marine food chains nearly reached
today’s complexity
Terrestrial food chains still appear to increase in complexity
By the end of the Cambrium all major marine and freshwater ecological niches were occupied, leaving
no room for additional aquatic born phyla.
Extinctions
R2 = 0.21p(t) < 0.0001
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Mass extinctions
Trade off between extinction and speciation
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The background extinction rate e(t) of marine taxa decreased!
Marine taxa
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Mass extinctions might be followed by high origination rates
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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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Ex
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Mass extinction
Brachiopoda
Bivalvia
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Mass extinction
Unbuffered species
Buffered species
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Mass extinction
Sessile species
Motile species
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Mass extinction
Predators
Prey
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
Data from Mc Peek, Brown (2007)
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.
Chordata
Arthropoda
Mollusca
Species richness and taxon age
Insecta and Vertebrata
The Red Queen hypothesis
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.
Leigh M. Van Valen 1935- 2010
y = 633e-0.038x
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Survival time [mya]
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Survival times for extinct genera of Echinoidea (sea urchins).
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Time (m ya)
Negative age dependent rate of extinction
Positive age dependent rate of extinction
Constant rate of extinction
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
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