Towards multicellularity
Four elements to make a multicelluar organism
Colonial
organization
Information
exchange
External
secretion
Apoptosis
Bacteria
•
•
•
•
•
Paenibacillus
forms colonies
moves on hard surfaces through jointly secreted lubricants
communicates with other cells
no apoptosis
no real cell differentiation
•
•
•
•
•
•
•
Myxobacteria
form colonies of millions of cells
Some have coordinated movements
form biofilms
largest bacterial genomes (9 - 12 kB)
some produce fruiting bodies for the release of spores
no apoptosis
rudimentary cell differentiation
Paenibacillus dendritiformis
Myxococcus xanthus
Why did Bacteria not evolve true multicellularity?
Maybe their limits in genome size do not allow for higher order differentiation.
Nanowires and electrical signalling
Geobacter sulfurreducens
Microbial electrical cell-cell
communication via nanowires may
be widespread in nature.
Four elements to make a multicelluar organism
Colonial
organization
Information
exchange
Apoptosis
External
secretion
Stigmergy:
indirect signalling by secretion
Vascular
plants
Specialized cells reproduce
High degree of
cell differentiation
Real tissues
Organs
No central coordination
Brown algae
Cell
differentiation
Metazoa
Fungi
Specialized cells reproduce
Cell differentiation
No real tissues
No organs
Early differentiation of germ line
High degree of cell differentiation
Real tissues
Organs
Central coordination
Multicellularity
probably monophyletic
Slime moulds
Chlorophytes
Specialized cells reproduce
Cell differentiation
Real tissues
No organs
Facultative multicellularity
Limited cell differentiation
No real tissues
No organs
Multiple origin of multicellularity in each of these groups
Facultative multicellularity
Rudimentary cell differentiation
No real tissues
No organs
The multi-taxon genome initiative
Single celled parasites of
Some species form colonies
Pseudomarine pulmonate snails
multicellular
colonies
Capsaspora Choanoflagellata
True multicellularity
Ichthyospora
Sphaeroforma arctica
Fungi
Nuclearia
Single celled free living
marine heterotroph
Metazoa
Parasitic
Free
living
Free
living
Ministeria
Chorallochytrium
Parasitic
Apusozoa
Amoebozoa
Nematostella
Single celled
marine heterotroph
Single celled terrestrial or
aquatic bacteriophages
Single celled
aquatic heterotroph
Corallochytrium
limacisporum
El Albani A. et al. 2010
First multicellular organisms (12 cm of size) of unknown type
appeared as early as 2 bilion years ago.
Single cell organisms
Parasites of marine fish,
birds and mammals
Some species form pseudomulticellular colonies
Ichthyospora
From Tonian to modern times
Ediacaran
630
Warmer
period
interrupted
by local
ice ages
Dickinsonia
Tribrachidium
Cryogenian
850
Rodinia
breaks up.
Largest
glaciations
(snowball
earth)
?
Cyclomedusa
Parvancorina
Biotracers of
Porifera
Charniodiscus
Spriggina floundersi
Tonian
1000
Supercontinent
Rodinia
Metazoa
Mesoproterozoicum
1600-1000
Parmia
Horodyksia
Maybe a colonial benthic two tissued
metazoan
Maybe a homonomous segmented metazoan
?
Photos from Fedonkin 2003
Cambrium
540
Canadia,
Annelida
Warmer period
Rangeomorpha were
fractal organisms
White sea
developing through
and Nama
simple branching
assemblages
patterns (like Fungi)
560
Warmer period
Avalon
assemblages
580
Warmer period
Increase in
atmospheric
O2 level
Middle
Ediacaran
600
Local ice ages
Early
Ediacaran
630
Warmer period
Kimberella,
Mollusca: like
Chiton
Charnia
Aspidella
Spriggina
Arthropoda:
Shallow water mobile
animals related to
modern taxa
Tateana
Advanced Rangeomorpha and
simpler Erniettomorpha
Probably not related to any modern taxon
Immobile, deep-water filter feeders
No mouth or gut, no reproductive organs
An early
embryo
Acritarch
A functional model of metazoan evolution
Placozoa
Porifera
Information exchange via neurotransmitters
Ectoderm
Mesogloa
Ciliate entoderm
Trichoplax
Nervous cells
A hypothetical creeping animal
of Gastrula organization
Statocyst
Cnidaria
Ctenophora
Acoela
Xenoturbellida
Deuterostomia s. str.
Lophotrochozoa
Ecdysozoa
A major invention: Metameria
Plathelminthes,
flatworms
Porifera,
Sponges
Cnidaria, see
anemone
Amorph body plan
Modular body plan
Monoform bilateral
body plan
Homonomous to
heterononous segmentation
Hallipterus excelsior
(Sea scorpions), Devon
Megascolides
australis
A fractal rangeomorph body plan (Ediacarium)
Fractal like
resource devilery
systems
Heteronoumus segmentation
modified into tagmata
Vertebrates,
Arthropods
Metameric
body plan
A major invention: Metameria
Christiane NüssleinVolhard (1942-)
Walter Jacob Gehring
(1939-2014)
All animals share a common gene family, the homeobox
family, that controls metameric and embryonal development.
Extended Hox
EHG box
Early
Vertebrates
EHG box Proto Hox
NKL
Proto NKL
Cnidaria
Early
Metameria
Para Hox
Arche Hox
Trichoplax
adhaerens
In Ctenophora Hox genes haven’t been detected yet.
Early
arthropods
The evolution of Hox genes
Homeotic genes:
MADS-box
Plants
Homeotic
genes
Fungi
Metazoa
Placozoa
Cnidaria
Metameria
Homeotic genes:
Hox-genes
From: http://users.rcn.com/
jkimball.ma.ultranet/BiologyPages/
H/HomeoboxGenes.html
Convergent
evolution of
genes that
regulate
ontogenetic
development
Eleutheria dichotoma,
Photo from Jacob and Schierwater
2007, Plos One 2: e694.
Inactivation of Cnox 3 in
the hydrozoan Eleutheria
dichotoma produces
multiple heads, for
instance head duplication
and therefore a bilaterian
pattern
Kinorrhyncha
Sipuncula
Onychophora
Entoprocta
Cycliophora
Loricifera
Chaetognatha
Hemichordata
Echinodermata, sea
stars, sea urchins)
Mesoproterozoicum
1600-1000
Tonian
1000-850
Cryogenian
850-680
Ediacaran
680-540
Blastoporus becomes anus
„Bilateria”
Ecdysozoa
Nervous cells, Statocyst Mesoderm
Gastrula, Muscle cells
Ecto-, Entoderm
Hox box
Multicellularity, nervous
cells, multiple bilaterality
Choanocytes
Upper and lower side
Deuterostomia
Protostomia
Multiple bilaterality
Ambulacraria
(Hemichordata,
Echinodermata)
Chordata
Metameria,
Coelom
Xenoturbellida
No anus
No coelom
Cycloneuralia
(Nematoda, Priapulida) Metameria
Onychophora
Pseudocoelom
Arthropoda
Lophotrochozoa
Nervous cells, Statocyst
Cambrian
540-490
Plathelminthes s. str. No anus
Pseudocoelom
Gnathifera
Mollusca
Annelida s. l.
Lophophorata
Acoela
Chaetognatha
Cnidaria
Paraphyletic
Placozoa
Porifera
Paraphyletic
Ctenophora
Choanoflagellata
Metameria,
Coelom
No anus,
No coelom
Pseudocoelom,
Anus,
Metameria
The molecular evidence
Cryogenian
850-630
Ediacaran
Mass
630-540 extinction
Ordovician
490-440
Cambrian
540-490
Silurian
440-410
Malacostraca Isopoda
Panarthropoda
(Tetraconata)
Maxillopoda
Branchiopoda
Tardigrada
Hexapoda
Cephalocarida
Remipedia
Mandibulata
Xeno
carida
Pancrustacea
Podocopa
Myodocopa
Ostracoda
Chilopoda
„Myriapoda”
Diplopoda
Pycnogonida
Chelicerata
Trilobites
Aglaspida
Onychophora
Aysheaia
Xiphosura, Arachnida
Beckwithia
typa
The Cambrian explosion
Cambrian 540-490
During the Cambrian atmospheric oxygen concentration increased to a level to allow for the
development of hard skeletons. Probably all today’s phyla were already present.
First complicated food webs including higher predators appeared.
This might have caused the disappearance of the Ediacaran fauna.
Waptia, Chelicerata?
An early predator
Burgessochaeta, Polychaeta
An early predator
Pikaia, Chordata
Chmatocrinus, Crinoidea
The earliest deuterostomes
Ottoia, Priapulida
An early predator
Olenoides serratus,
Trilobites
Ordovician 490-440
Warm shallow seas
Silurian 440-410
Ice age
Warm greenhouse phase (high CO2 level)
Mass extinction
First Cephalopoda (Nautiloids) and Bivalvia. Rise of
Brachiopoda and Bryozoa.
Trilobites Arthropoda
Bryozoa
First primitive terrestrial fungi, vascular
plants and animals (millipedes,
arachnids)
Eurypterus
remipes,
Chelicerata
Cooksonia grade
land plants
Cephalopoda
Conodonts
Birkenia, Agnatha
Why did nearly all phyla of animals evolve in the Ediacarian?
Basal
genetic
program
HOX
genetic
program
Subsequent
genetic
programs
Subsequent
genetic
programs
Zygote
Mutation: Failure of further development
Gastrula
Porifera
Mutation: Highly aberrant body plan
Cnidaria
Ctenophora
Mutation: Differences in
body plan
Plathelminthes
Mutation: Differences in
body functioning
Metameria
Annelida
Arthropoda
Vertebrata
Subsequent genetic programs
Pipunculidae
Today’s reading
Ediacara fauna and the origin of Metazoa:
http://www.peripatus.gen.nz/paleontology/Ediacara.html
http://www.ucmp.berkeley.edu/vendian/critters.html
The Burgess shale: http://www.gpc.edu/~pgore/geology/geo102/burgess/burgess.htm
http://www.palaeos.com/Paleozoic/Cambrian/Cambrian.htm
The history of life: http://www.palaeos.com/
The tree of life: http://www.tolweb.org/tree/
The virtual fossil museum: http://www.fossilmuseum.net/
On the cambrian explosion:
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1578734
Metazoan phylogeny: the state of art.:
http://icb.oxfordjournals.org/cgi/content/full/46/2/93
Dunn C. W. et al. (2008) Broad phylogenomic sampling improves resolution of the animal tree
of life. Nature 452: 745-750.
Srivastava M. et a. 2008. The Trichoplax genome and the nature of placozoans. Nature 453:
855-960..