Evolution lectures 3&4 September 2013

Mini-summary of lectures 1 & 2
Monday, 30 September 13

Speciﬁc Questions/Comments
Geologists (Hutton, Lyell):
Uniformitarianism: Changes in nature are gradual.
In 1800s, fossils showed species that no longer existed:
Some (e.g. Cuvier):
Catastrophism: Fossils show extinct species (due to major,
sudden, catastrophic events).

3 Schools of evolutionary thought
• Lamarck: characteristics acquired by an
individual are passed on to offspring.
• Linneaus: each species was separately
created.
• Darwin & Wallace: evolution as
descent with modiﬁcation.

Evolution by Natural Selection
• There is inherited variation within species.
• There is competition for survival within species.
• Genetically inherited traits affect reproduction or survival.Thus
the frequencies of variants change.
(Not just numbers of offspring!)
Evolutionary ﬁtness:
A measure of the ability of genetic material to perpetuate itself
in the course of evolution. Depends on the individual’s ability to
survive, the rate of reproduction and the viability of offspring.

“Neo-Darwinism”
or
“The Modern Synthesis”
The same thing... but with better
understanding of how things work.
• Darwin’sTheory of Evolution by Natural Selection (1859)
• Mendel’s Laws of Heredity (1866, 1900; see SBS 008)
• Cytogenetics (1902, 1904 - )
• Population Genetics (1908; see Lectures 7-12)
• Molecular genetics (1970s- ; see SBS 633/210 and Lecture 6)
•More stuff since then (cultural evolution, epigenetics, etc...)

•Evolution also occurs by:
•genetic drift
•sexual selection
•...
Natural selection leads to adaptive
change
•But environmental conditions change:
What was advantageous yesterday may be a disadvantage today.
But not all change is adaptive!

Paperback 596 pages
(11 Aug 2005)
Publisher: Oxford University Press

1. The Fossil Record
2. Comparative Anatomy
3. Comparative Embryology
4. Vestigial Structures
5. Domestication (artiﬁcial selection)
Darwin’s evidence for evolution

Geological times & continental drift

Today
1. Major transitions in evolution
2. Geological timescales
3. Major geological drivers of evolution
4. Recent major extinction events

Major transitions?
1.Smaller entities coming together to form larger entities. (e.g.
eukaryotes, multicellularity, colonies...)
2.Smaller entities become differentiated as part of larger entity. (e.g.
organelles, anisogamy, tissues, castes...)
3.Smaller entities are often unable to replicate without the larger entity.
(e.g. organelles, tissues, castes...).
4.The smaller entities can disrupt the development of the larger entity,
(e.g. Meiotic drive, parthenogenesis, cancer...)
5.New ways of transmitting information arise (e.g. DNA-protein,
indirect ﬁtness...)
Maynard Smith and Szathmary 1995

Major transitions: early life
1953 Miller-Urey “primitive soup”
experiment
350° vs 0°
➔ organic molecules

•Organic molecules ≠ Life
•Early life:
•Hereditary replication
•Compartmentalization
•First hereditary information?

Phylogenetic Tree of Life
Bacteria
Green
Filamentous
bacteriaSpirochetes
Gram
positives
Proteobacteria
Cyanobacteria
Planctomyces
Bacteroides
Cytophaga
Thermotoga
Aquifex
Halophiles
Methanosarcina
Methanobacterium
Methanococcus
T. celer
Thermoproteus
Pyrodicticum
Entamoebae
Slime
molds
Animals
Fungi
Plants
Ciliates
Flagellates
Trichomonads
Microsporidia
Diplomonads
Archaea Eukaryota
last universal common
ancestor (LUCA)
Woese 1990 tree based on ribosomalRNA sequences

•Organic molecules ≠ Life
•Early life of simple replicators:
•Hereditary replication
•Compartmentalization
•First hereditary information?
•Probably RNA: Genetic information (that can be copied)
+ Enzymatic activity.
•Amino-acids (initially as co-factors)
•DNA (much more stable than RNA)
•Linkage of replicators (chromosomes)

Major transitions: Prokaryote to Eukaryote
Prokaryotic cell
Cell membrane
infoldings
Cell membrane
Cytoplasm
Nucleoid
(containingDNA)
Endomembrane system
Endoplasmic reticulum
Nuclear membrane
Nucleus
Proteobacterium
Mitochondria
Cyanobacterium
Chloroplasts
Mitochondrion
†
†
†
1 Aprokaryote grows in size
and develops infoldings in its
cell membrane to increase its
surface area to volume ratio.
2 The infoldings eventually pinch off
from the cell membrane, forming
an early endomembrane system.
It encloses the nucleoid, making a
membrane-bound nucleus.
This is the first eukaryote.
3
5 Some eukaryotes go on to acquire add
endosymbionts—the cyanobacteria, a g
of bacteria capable of photosynthesis.
They become chloroplasts.
Ancestor of plants and algæ
Ancestor of animals, fungi,
and other heterotrophs
First eukaryote
The aerobe's ability to use
oxygen to make energy be-
comes an asset for the host,
allowing it to thrive in an in-
creasingly oxygen-rich environ-
ment as the other eukaryotes
go extinct. The proteobacterium
is eventually assimilated and
becomes a mitochondrion.
Some eukaryotes go on to ac-
quire additional endosymbionts
— the cyanobacteria, a group of
bacteria capable of photosynthe-
sis. They become chloroplasts.Anaerobic (oxygen using) proteo-
bacterium enters the eukaryote,
either as prey or a parasite, and
manages to avoid digestion. It
becomes an endosymbiont, or a
cell living inside another cell.

Major transitions: sex
•See lectures Week 5.

Major transitions: multicellularity

Major transitions: multicellularity
Green algae: Inspiration for what may have occurred: Volvocales

e.g.: artiﬁcial selection for
multicellularity in S. cerevisiae yeast
Ratcliff et al 2012

Volvox
Somatic cells
Gonidia

Major transitions:
eusociality
•Solitary lifestyle --> Eusociality
1. Reproductive division of labor
2. Overlapping generations (older
offspring help younger offspring)
3. Cooperative care of young
Eg: ants, bees, wasps, termites. But also:
naked mole rats, a beetle, a shrimp...

Hamilton, 1964
Major transitions: eusociality
•Kin selection: can favor the reproductive success of an organism's
relatives (ie. indirect fitness), even at a cost to the organism's own
survival and reproduction.
•Hamilton’s rule: genes for altruism increase in frequency when:
indirect fitness benefits to the receiver (B) ,
B
exceeds costs to the altruist (C).
> Cr ×
reduced by the coefficient of relatedness (r),

© National Geographic
Atta leaf-cutter ants

Oecophylla Weaver ants
© ameisenforum.de

© ameisenforum.de
Fourmis tisserandes

© ameisenforum.de
Oecophylla Weaver ants

Tofilski et al 2008
Forelius pusillus

Tofilski et al 2008
Forelius pusillus hides the nest entrance at night

Avant
Workers staying outside die
« preventive self-sacriﬁce »
Tofilski et al 2008
Forelius pusillus hides the nest entrance at night

Dorylus driver ants: ants with no home
© BBC

Animal biomass (Brazilian rainforest)
from Fittkau & Klinge 1973
Other insects Amphibians
Reptiles
Birds
Mammals
Earthworms
Spiders
Soil fauna excluding
earthworms,
ants & termites
Ants & termites

elisa.piccaro@qmul.ac.uk
Send
your student id & tell her to add
you to this module.
If QMPlus isn’t working

“Complexity of life” didn’t
increase linearly.
2. Geological time scales
Deﬁned by changes in ﬂora and fauna (seen in fossil record).
Eon > Era > Period > Epoch

4550 Ma:
Hominids
Mammals
Land plants
Animals
Multicellular life
Eukaryotes
Prokaryotes
Hadean
Archean
Proterozoic
Paleozoic
Mesozoic
Cenozoic
4527 Ma:
Formation of the Moon
4.6 Ga
4 Ga
3.8Ga
3 Ga
2.5 Ga
2 Ga
1 Ga
542
M
a
251 Ma
65 Ma ca. 4000 Ma: End of the
Late Heavy Bombardment;
first life
ca. 3500 Ma:
Photosynthesis starts
ca. 2300 Ma:
Atmosphere becomes oxygen-rich;
750-635 Ma:
wo Snowball Earths
ca. 530 Ma:
ambrian explosion
ca. 380 Ma:
First vertebrate land animals
230-65 Ma:
Dinosaurs
2 Ma:
First Hominids
Ga = Billion years ago
Ma = Million years ago
Eon
Eon
Eon
Era
Era
Era
Phanerozoic
Eon
Geological timescales: Eon > Era >
Period > Epoch

End of Proterozoic biota
Dickinsonia

Trilobites
Cambrian to late permian

50100150200250300350400450500 0542
0
1
2
3
4
5
Millions of Years Ago
ThousandsofGenera
Cm O S D C P T J K Pg N
Biodiversity during the Phanerozoic
All Genera
Well-Resolved Genera
Long-Term Trend
The “Big 5” Mass Extinctions
Other Extinction Events

Earth
Life
Eukaryotes
H
om
o
sapiens: 5
m
eters
W
hitechapel: D
inosaurs
extin
N
H
M
:ﬁrst
tetrapod
Ham
m
ersm
ith:Cam
brian
explosion

•Tectonic movement (of continental plates)
•Vulcanism
•Climate change
•Meteorites
Conditions on earth change.

Plate tectonics
12
3
54

Crustal plates and continental drift

Recent continental
movements...
TETHYS
SEA
LAURASIA
GONDWANA
EquatorTriassic 200
Mya
Pangaea - single
supercontinent

Fossil distribution
Gondwana

Earthquakes
•Some tectonic movement is violent.
•E.g. 2004 Sumatra earthquake & tsunami...

Vulcanism
•Local climate change (e.g. thermal vents, hot springs...)
•Global climate change: Emission of gasses & particles.
•New geological barriers (migration...)
•New islands (“Malay archipelago”,
Galapagos... Hawaii... )
Deccan traps
Eyjafjall
ajokull

Climate change
(since Cambrian)

Vulcanism
Tectonic movement
Meteorite impact
Climate change?
?
Consequences: • Large scale migrations
• Speciation
• Mass extinctions
• Adaptive radiations

4. Recent major extinction events
Pg
fraction of genera present in
each time interval but extinct in
the following interval
KT:K-PgCretaceous–Paleogene
T
riassic-Jurassic
Perm
ian-Triassic
LateDevonian
Ordovician–Silurian
Today

•Oxygen levels.
•Tetrapods and early amniotes.
•Tropical conditions around equatorial landmasses.
• Damp forests: tall trees & lush undergrowth: giant club mosses,
lycopods, ferns & seed ferns.
• Decaying undergrowth forms coal.
• Good habitats for terrestrial invertebrates including spiders,
millipedes and insects (e.g. giant dragonﬂies).
Pangaea - single
supercontinent
Carboniferous/Permian

Dimetrodon
(sub-class Synapsida = “mammal-like reptiles”)
Early Permian mammal-like reptiles

Permian-Triassic Extinction
Sun et al Science 2012
Went extinct:
•Up to 96% of marine species & 70% of terrestrial vertebrates
•21 terrestrial tetrapod families (63%)
• 7 orders of insects

Jurassic/Cretaceous
•Mammal-like reptiles were replaced
as dominant land vertebrates by
reptiles (dinosaurs).
• Lizards, modern amphibians and
early birds appear.
• The conifer- and fern-dominated
vegetation of the LateTriassic
continued into the Jurassic.

Cretaceous–Paleogene (KT) extinction
66 million years ago
Subsequently, many adaptive radiations to ﬁll newly vacant niches.
eg. mammals, ﬁsh, many insects
Ammonite
Mosasaur
(marine reptile) Non-bird
dinosaurs
Most Plant-eating insects
75% of all species became extinct (50% of genera).
Including:

http://www.scotese.com/earth.htm)

Evidence for Chixulub impact
Magnetic ﬁeld near site
Crater: 180km diameter; bolide: 10km.

•Bolide impact at Chixulub.
•huge tsunamis
•cloud of dust and water vapour, blocking sun.
•plants & phytoplankton die (bottom of food chain)
--> animals starve
•dramatic climate & temperature changes are
difﬁcult (easier for warm-blooded?)
•Additional causes?
•Some groups were ALREADY in decline
•Additional impacts?
•Deccan traps (India) - 30,000 years
of volcanic activity (lava/gas release)

Diprotodon,
Australia, extinct 40,000 ya
Dodo,
Mauritius, extinct since 1662
Ongoing Anthropocene extinction
•Hunting
•Habitat destruction, modiﬁcation & fragmentation
Passenger
Pigeon
North America;
extinct since
1914.
Glyptodon,
Americas, extinct ~12000
years ago

Ongoing Anthropocene extinction
•Hunting
•Habitat destruction,
modiﬁcation & fragmentation
•Pollution/Overexploitation
•Spread of invasive species - &
new pathogens
•Climate change

Rainforest loss in Sumatra
Margono et al 2012

Summary.
•The history of the earth is divided into geological time periods
• These are deﬁned by characteristic ﬂora and fauna
•Large-scale changes in biodiversity (mass extinctions) were triggered
by continental movement and catastrophic events

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Week 3: Fossils, DNA and Molecules
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Evolution lectures 3&4 September 2013

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