Download Major transitions in evolution

Maynard Smith & Szathmary (1995)
Walter Salzburger:
Major
Transitions
in Evolution
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from
to
1
replicating molecule
populations of molecules in compartments
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independent replicators
chromosomes
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RNA as gene and enzyme
DNA genes, protein enzymes
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bacterial cell (prokaryotes)
cells with nuclei, organelles (eukaryotes)
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asexual clones
sexual populations
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protists (single-celled)
animals, plants, fungi
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solitary individuals
colonies (non-reproductive casts)
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primate societies
human societies (language)
Maynard Smith & Szathmary (1995)
Major transitions in evolution
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Major transitions in evolution
molecules - populations of molecules
! The first objects with the properties of multiplication,
variation and heredity were replicating molecules, similar to
RNA but perhaps simpler
! These molecules were not informational, because they did
not code for other structures
! In a protocell, populations of replicating molecules were
enclosed within some kind of membrane (“compartment”)
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Major transitions in evolution
molecules - populations of molecules
replicating
molecule
metabolic
product
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Major transitions in evolution
molecules - populations of molecules
protocell
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Major transitions in evolution
Stromatolites
! ...are witnesses of the oldest known fossils,
dating back to up to 3.5 billion years
! ...are layered structures that have been
formed by cyanobacteria and other microbes
www.discoverwest.com.au
! ...are formed when cells grow on the sea
surface, and sediments are deposited
among or above the cells. The cells then
grow up to the light, leaving a mineralized
layer below them.
! Cyanobacteria were likely responsible for
the creation of earth’s oxygen and, today,
are nearly extinct
www.futura-sciences.com
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Major transitions in evolution
replicators - chromosomes
! In living organisms, replicating molecules (“genes”) are
linked together end to end to form chromosomes. Most
simple organisms have a single chromosome per cell.
! This has the effect that when one gene is replicated, all are
(coordinated replication)
! This situation favors co-operation between genes in a
compartment.
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Major transitions in evolution
replicators - chromosomes
chromosome
cell
gene
protein
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Major transitions in evolution
RNA - DNA and proteins
! Today, there is a division of labor between two classes of
molecules: nucleic acids (DNA, RNA) and proteins
! Nucleic acids store and transmit information, proteins
catalyze chemical reactions and form structure (e.g.,
muscles, hair)
! I seems likely that, initially, this division did not exist and
that RNA performed both functions
! The transition from this “RNA world” to the world of DNA
and proteins required the evolution of the genetic code
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Major transitions in evolution
RNA - DNA and proteins
ribozyme
transfer RNA (tRNA)
messenger RNA (mRNA)
GC
UGAUUGA
AUAU
CGUGUCA
micro RNA (miRNA)
ribosomal RNA (rRNA)
images: www.whatislife.com, www.rothamsted.ac.uk, www.wikipedia.org, www.aps.anls.gov
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Major transitions in evolution
www.fig.cox.miami.edu
RNA - DNA and proteins
transcription
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Major transitions in evolution
www.fig.cox.miami.edu
RNA - DNA and proteins
translation
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Major transitions in evolution
Ridley (1996)
RNA - DNA and proteins
genetic code
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Major transitions in evolution
prokaryote - eukaryote
• relatively simple
• no nucleus (i.e., DNA lies in no particular region)
prokaryote cell
• a single circular chromosome (most often)
• small ribosomes
• in two of the three domains of life (bacteria, archaea)
• complex internal structure
• DNA is organized in the nucleus
eukaryote cell
• more than one chromosome
• organelles (mitochondria, chloroplasts)
• large ribosomes
• in all complex multicellular organisms
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Major transitions in evolution
prokaryote - eukaryote
endosymbiont hypothesis
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Major transitions in evolution
prokaryote - eukaryote
three domains of life
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Major transitions in evolution
asexual - sexual reproduction
Hydra
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Major transitions in evolution
asexual - sexual reproduction
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Major transitions in evolution
asexual - sexual reproduction
Haplodiploid life cycle without fusion
endomitosis
One-step meiosis
! Genome duplication followed by a simple form of meiosis
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Major transitions in evolution
asexual - sexual reproduction
Life cycle with syngamy and a one-step meiosis
cell fusion
One-step meiosis
! Endomitosis is replaced by fusion; this is a sexual cycle
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Major transitions in evolution
asexual - sexual reproduction
Modern sexual life cycle
cell fusion
two-step meiosis
! Two-step meiosis is only found in eukaryotes
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Major transitions in evolution
protists - animals, plants, fungi
! Protists exist as single cells (or sometimes colonies)
! Animals, plants, fungi are composed of many different kinds of
cells. Therefore, each individual carries many thousands to
millions copies of the genetic information
! Although - in animals, plants and fungi - all cells contain the
same information, they are very different in shape,
composition, function, etc.
! Multicellularity most likely evolved three times in eukaryotes
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Major transitions in evolution
protists - animals, plants, fungi
ephithelial cells
macrophage cell
muscle cells
blood cells
pigment cells
images: www.nikonsmallworld.com,
www.astrographics.com,
www.dundee.ac.uk, www.esa.int,
www.protist.biology.washington.edu
nerve cell
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true animals
(metazoa)
plants
true fungi
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Major transitions in evolution
solitary individuals - colonies
Social insects:
www.apple.com
Some animals, notably ants, bees, wasps and
termites, live in colonies in which only a few
individuals reproduce. Such colonies have been
likened to a superorganism, analogous to a
multicellular organism.
The sterile workers are analogous to body cells,
and the reproducing individuals to the cells of
the germ line.
www.epfl.ch
It has been estimated that one-third of the
animal biomass of the Amazon rainforest
consists of ants and termites. The same might
be true for other habitats as well.
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Major transitions in evolution
solitary individuals - colonies
groups
nr. of eusocial species
Isoptera
all termites
Homoptera
some gall aphids
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Hymenoptera
hover wasps (Stenogastinae)
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independent-founding paper wasps
(Polistinae)
630
swarm-founding paper wasps (Polybiini)
400
yellowjackets, hornets (Vespinae)
78
sweat bees (Halictinae)
400
bumble bees (Bombinae)
200
honey bees (Apini)
2200
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stingless bees (Meliponinae)
280
ants (Formicidae)
9500
eusocial insects
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www.nmnh.si.edu
Major transitions in evolution
www.nationalgeogrpahic.com
solitary individuals - colonies
www.cs.dartmouth.edu
leaf cutter ant
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Major transitions in evolution
primate - human (language)
chimpanzee
human
gorilla
orangutan
rhesus macaque
evolution of language
Was language the
decisive step in the
transition from an ape to
a human society?
images: National Geographic, Leonardo da Vinci
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