Towards multicellularity
Colonial organization
Information exchange
ApoptosisExternal secretion
Four elements to make a multicelluar organism
Paenibacillus dendritiformis
Bacteria
Paenibacillus•forms colonies•moves on hard surfaces through jointly secreted lubricants•communicates with other cells•no apoptosis•no real cell differentiation
Myxococcus xanthus
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
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.
Colonial organization
Information exchange
ApoptosisExternal secretion
Four elements to make a multicelluar organism
Vascular plants
Brown algae Slime moulds
Fungi
Metazoa
Cell differentiation
Specialized cells reproduceHigh degree of cell differentiationReal tissuesOrgansNo central coordination
Early differentiation of germ lineHigh degree of cell differentiationReal tissuesOrgansCentral coordinationSpecialized cells reproduce
Cell differentiationNo real tissuesNo organs
Specialized cells reproduceCell differentiationReal tissuesNo organs
Facultative multicellularityRudimentary cell differentiationNo real tissuesNo organsMultiple origin of multicellularity in each of these groups
Multicellularity probably monophyletic
Stigmergy:indirect signalling by secretion
ChlorophytesFacultative multicellularityLimited cell differentiationNo real tissuesNo organs
The multi-taxon genome initiative
Amoebozoa
Ichthyospora
Sphaeroforma arctica
Capsaspora
Nuclearia
Fungi
Metazoa
Choanoflagellata
Apusozoa
Ministeria
Pseudo-multicellular colonies
Nematostella
Single celled parasites of marine pulmonate snails
Some species form colonies
Chorallochytrium
Corallochytriumlimacisporum
Free living
Parasitic
Free living
True multicellularity
Single celled aquatic heterotroph
Single celled marine heterotroph
Parasitic
Single celled free living marine heterotroph Single celled terrestrial or
aquatic bacteriophages
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 pseudo- multicellular colonies
Ichthyospora
Tonian1000Super-
continent Rodinia
Cryogenian850
Rodinia breaks up.Largest
glaciations (snowball
earth)
Ediacaran630
Warmer period
interrupted by local ice ages
?
Metazoa
Charniodiscus
Dickinsonia Tribrachidium
Spriggina floundersi
ParvancorinaCyclomedusa
?
From Tonian to modern times
Horodyksia
Maybe a colonial benthic two tissued metazoan
Meso-protero-zoicum
1600-1000
Parmia
Maybe a homonomous segmented metazoan
Photos from Fedonkin 2003
Biotracers of Porifera
Early Ediacaran
630 Warmer period
Middle Ediacaran
600 Local ice ages
Avalon assemblages
580 Warmer period
Increase in atmospheric
O2 level
White sea and Nama
assemblages560
Warmer period
Cambrium540
Warmer period
Aspidella
Advanced Rangeomorpha and simpler ErniettomorphaProbably not related to any modern taxon
Charnia
Shallow water mobile animals related to
modern taxa
Immobile, deep-water filter feedersNo mouth or gut, no reproductive organs
Rangeomorpha were fractal organisms developing through simple branching patterns (like Fungi)
An early embryo
Kimberella, Mollusca: like
Chiton
Spriggina Arthropoda:Canadia,
Annelida
Tateana
Acri-tarch
Ectoderm
Ciliate entoderm
Nervous cellsPorifera
Statocyst
PlacozoaInformation exchange via neurotransmitters
Trichoplax
A functional model of metazoan evolution
A hypothetical creeping animal of Gastrula organization
CtenophoraCnidaria
Acoela
Xeno-turbel-lida
Deuterostomia s. str. Lophotrochozoa Ecdysozoa
Mesogloa
A major invention: Metameria
Megascolides australis
Homonomous to heterononous segmentation
Hallipterus excelsior (Sea scorpions), Devon
Plathelminthes, flatworms
Porifera, Sponges
Cnidaria, see anemone
Amorph body plan Modular body planMonoform bilateral
body plan
A fractal rangeomorph body plan (Ediacarium)
Metameric body plan
Fractal like resource devilery systems
Vertebrates, Arthropods
Heteronoumus segmentation modified into tagmata
A major invention: Metameria
Christiane Nüsslein-Volhard (1942-)
Arche Hox
EHG box Proto Hox Proto NKL
EHG box Extended Hox NKL Para HoxEarly Vertebrates
Early arthropods
All animals share a common gene family, the homeobox family, that controls metameric and embryonal development.
Trichoplax adhaerens
Early Metameria
Cnidaria
Walter Jacob Gehring (1939-2014)
In sponges and Ctenophora Hox genes haven’t been detected yet.
Plants
Fungi
Metazoa
Homeotic genes: MADS-box
Homeotic genes
Homeotic genes: Hox-genes
Convergent evolution of genes that regulate ontogenetic development
Cnidaria
Metameria
Placozoa
From: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/HomeoboxGenes.html
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
The evolution of Hox genes
Kinorrhyncha Onychophora
Chaetognatha
Hemichordata Echinodermata, sea stars, sea urchins)
LoriciferaEntoprocta
Cycliophora
Sipuncula
Porifera
Choanoflagellata
Placozoa
Ctenophora
Cnidaria
Plathelminthes s. str.
Cycloneuralia(Nematoda, Priapulida)
Lophotrochozoa
Chordata
Mul
ticel
lula
rity,
Hox
box
„Bilateria”
Protostomia
Blastoporus becomes anus
Cho
anoc
ytes
Upp
er a
nd lo
wer
sid
e
ParaphyleticMultiple bilaterality
Gas
trul
a, M
uscl
e ce
lls
Metameria, Coelom
Ect
o-, E
ntod
erm
Cnidocytes, Rhopalia
Ner
vous
cel
ls, S
tato
cyst
Acoela
Xenoturbellida
Cryogenian850-680
Ediacaran680-540
Tonian1000-850
Cambrian540-490
Mesoproterozoicum1600-1000
Ambulacraria (Hemichordata, Echinodermata)
Chaetognatha
Onychophora
Arthropoda
Gnathifera
Annelida s. l.Mollusca
Deuterostomia
Ecdysozoa
MetameriaPseudocoelom
Metameria, Coelom
Mes
oder
m
Pseudocoelom
No anus, No coelom
No anus
No anusNo coelom
Lophophorata
Pseudocoelom, Anus, Metameria
Paraphyletic
Cryogenian850-630
Ediacaran630-540
Cambrian540-490
Mass extinction
Onychophora
Trilobites
The molecular evidence
ChelicerataXiphosura, Arachnida
Pycnogonida
Pancrustacea
„Myriapoda”Diplopoda
Chilopoda
Myodocopa
Podocopa
Remipedia
Ordovician490-440
Silurian440-410
Hexapoda
Branchiopoda
Maxillopoda
Malacostraca
Aysheaia
Beckwithia
typa
Aglaspida
Cephalocarida
Isopoda
Ostra-coda
Tardigrada
Panarthropoda(Tetraconata)
MandibulataXenocarida
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
Ottoia, PriapulidaAn early predator
Chmatocrinus, CrinoideaThe earliest deuterostomes
Pikaia, ChordataOlenoides serratus,
Trilobites
Ordovician 490-440 Silurian 440-410
Ice ageMass extinction
First primitive terrestrial fungi, vascular plants and animals (millipedes,
arachnids)
Eurypterus remipes,
Chelicerata
First Cephalopoda (Nautiloids) and Bivalvia. Rise of Brachiopoda and Bryozoa.
Warm shallow seas Warm greenhouse phase (high CO2 level)
Trilobites Arthropoda Bryozoa
Cephalopoda
ConodontsBirkenia, Agnatha
Cooksonia grade land plants
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.htmlThe Burgess shale: http://www.gpc.edu/~pgore/geology/geo102/burgess/burgess.htm
http://www.palaeos.com/Paleozoic/Cambrian/Cambrian.htmThe 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..