zoo4 honours mark blaxter 2007-2008 arthropod origins and relationships
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ZOO4 HONOURSMark Blaxter 2007-2008 www.nematodes.org
ARTHROPOD ORIGINS AND RELATIONSHIPS
Arthropod origins and relationships
Three main questions:
1. Is Arthropoda a monophyletic group?
2. Which non-arthropod groups are most closely related to Arthropoda?
3. What are the relationships among different arthropod groups?
NB: these questions are inextricably interlinked…
Why do these questions matter?• Inform models of metazoan evolution -
what is the pattern of evolution of morphological and physiological novelty? Are there general evolutionary ‘laws’?
• Arthropods are ~80% of described diversity.
Arthropod origins and relationships
Three main questions:1. Is Arthropoda a monophyletic group?2. Which non-arthropod groups are most
closely related to Arthropoda?3. What are the relationships among
different arthropod groups?
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
So:
Reptilia is only MONOPHYLETIC if we include Aves
The taxon “marine mammals” is not monophyletic within Mammalia (as it excludes groups that last shared a common ancestor with some non-marine mammals since the last common ancestor of all marine mammals)
Is Arthropoda Monophyletic?
According to ‘traditional’ systematic taxonomies,there are four extant classes within Arthropoda
CHELICERATA spiders and alliesMYRIAPODA centipedes and alliesCRUSTACEA crabs and alliesHEXAPODA insects and allies
There is one extinct class
TRILOBITA the trilobites
Trilobites
AncientMarineNo jawsGills on limbs
Chelicerates
Spiders Ticks and Mites Solifuges
Scorpions PseudoscorpionsAmblypygids
Ancient, originally marine, chelicerae, book gills/lungs
Horseshoe crabs
Pycnogonids
Myriapods
Ancientoriginally marineMandiblesTracheae
Crustacea
AncientOriginally marineMandiblesGills on limbs
Hexapoda
YoungTerrestrialMandiblesTracheae
InsectaDipleuraEllipleura
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
What defines “Arthropoda”?
Bilaterally symmetrical, triploblast, protostomious
Coelomate, but coelom reduced to reproductive and excretory systems
Body cavity is a haemocoel; circulatory system is open
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
What defines “Arthropoda”?
Bilaterally symmetrical, triploblast, protostomious
Coelomate, but coelom reduced to reproductive and excretory systems
Body cavity is a haemocoel; circulatory system is open
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
What defines “Arthropoda”?
Bilaterally symmetrical, triploblast, protostomious
Coelomate, but coelom reduced to reproductive and excretory systems
Body cavity is a haemocoel; circulatory system is open
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
What defines “Arthropoda”?
Segmented internally and externally
Teloblastic growth
Tagmosis (minimally cephalon and trunk)Cephalon includes nonsegmental acron and labrum;
Cephalon with lateral faceted eyes and median ocelli
Each segment with appendages
with proximal protopod and distal telopod
Gut complex and regionalised
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
What defines “Arthropoda”?
Segmented internally and externally
Teloblastic growth
Tagmosis (minimally cephalon and trunk)Cephalon includes nonsegmental acron and labrum;
Cephalon with lateral faceted eyes and median ocelli
Each segment with appendages
with proximal protopod and distal telopod
Gut complex and regionalised
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
What defines “Arthropoda”?
Segmented internally and externally;
Teloblastic growth
Tagmosis (minimally cephalon and trunk)
Cephalon includes nonsegmental acron and labrum;
Cephalon with lateral faceted eyes and median ocelli
Each segment with appendages
with proximal protopod and distal telopodGut complex and regionalised
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
What defines “Arthropoda”?
Musculature metameric; No circular somatic musculature; Dorsal and ventral longditudinal muscles present
Dorsal CNS ganglia (protocerebrum is ocular, deuterocerebrum antennal)
Paired ventral nerve cords and ganglia
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
What defines “Arthropoda”?
Musculature metameric; No circular somatic musculature; Dorsal and ventral longditudinal muscles present
Dorsal CNS ganglia (protocerebrum is ocular, deuterocerebrum antennal)
Paired ventral nerve cords and ganglia
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
What defines “Arthropoda”?
Musculature metameric; No circular somatic musculature; Dorsal and ventral longditudinal muscles present
Dorsal CNS ganglia (protocerebrum is ocular, deuterocerebrum antennal)
Paired ventral nerve cords and ganglia
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
What defines “Arthropoda”?
Cilia absent except in some sperm
Growth by moulting (ecdysis) mediated by ecdysone
Cuticular exoskeleton with chitin and resilin/cuticlin, NOT collagen; sometimes calcified
Is Arthropoda Monophyletic?
Monophyly: a natural group that includes ALL the descendents of a particular ancestor
What defines “Arthropoda”?
Could these characters have arisen multiple times, independently?
Could the arthropod “grade” have evolved more than once from a common ancestor with the Annelida?
(HOMOPLASY - the convergent evolution of shared characters)
Which non-arthropod groups are most closely related to Arthropoda?
?
(if all arthropods share the same ancestors, they will be monophyletic)
Which non-arthropod groups are most closely related to Arthropoda?
The common ancestor of all Arthropods was probably a ‘lobopod’, similar to extant onychophorans and tardigrades
Onychophorathe velvet worms
TerrestrialSoft-bodiedSegmentedLobopod legsRareViviparousSmallish (cm)
patchy fossil record, but present in Burgess Shale and other faunas (marine)
Tardigradathe water bears
Terrestrial and marineOviparousSoft-bodiedSegmentedLobopod legsCommonTiny (~1 mm or less)
essentially absent from the fossil record
Is Arthropoda Monophyletic?
S. Manton and D. Anderson suggested that Arthropoda was polyphyletic
3 independent origins of the arthropod “grade”
HexapodsMyriapods
Onychophorans
Crustacea
Trilobites
Chelicerates
Uniramous limbs
Tracheal system
Biramous limbs
1
2
3These groups also differ in patterns of segmentation in the head
No mandibles
Is Arthropoda Monophyletic?
Polyphyletic origin hypotheses have been tested and are less likely than a monophyletic origin
Support for monophyly comes from
Molecular phylogenetic data (that excludes Onychophora and Tardigrada)
Gene arrangements in the mitochondrial genome
Patterns of expression of HOX genes during development
Analysis of limb development and evolution
Close analysis of “tracheal” systems
Which non-arthropod groups are most closely related to Arthropoda?
Panarthropoda
Tardigrada Onychophora Arthropoda
Which non-arthropod groups are most closely related to Arthropoda?
Panarthropoda
TardigradaOnychophora Arthropoda
Do fossils help?
Are there “intermediate” fossils that will help in clarifying the relationships of arthropods and other animals?
Do fossils help?Lagerstätten - fossilifierous sediments with exquisite preservation even of soft-bodied fauna and soft parts of those with shells.see http://palaeo.gly.bris.ac.uk/Palaeofiles/Lagerstatten/
Burgess Shale, Canada 505 MYaSirius Passet, Greenland 518 MYaChengjiang, China 530 MYa
phosphatic sedimentsDoushantuo, China 590-540 MYa
Ediacaran assemblagesEdiacara, Australia 560-540
MYaMistaken Point, NewfoundlandCharnwood Forest, UK
The Burgess Shale location, Jasper National Park, Canada
Burgess Shale animals were killed and covered by the collapse of a marine reef
reconstructions...
Cambrian arthropods from the Burgess Shale
Aysheaia
Chelicerate
Hallucigenia
Trilobite
Crustacean
Onychophorans
Some are ~easily~ slotted into “standard” places in Arthropoda
Cambrian arthropods from the Burgess Shale
Marella
Opabinia
Anomalocaris
Sidneya
...but for others, it is much less easy to shoehorn them into current taxa
Sirius Passet deposits are older, but have some similar taxa
Lagannia, an anomalocarid
...and some unique ones:
Kergymachela
Chienjiang deposits are still above the origin of arthropods
Doushantuo fossils are smallThe animal fossils are EMBRYOS
The Ediacara “fauna” is, at best, enigmatic
Spriggina,a trace fossil, or an arthropod, or an annelid?
Dickinsonia
Tribrachidium
Pteridinium
Do fossils help?
Are there “intermediate” fossils that will help in clarifying the relationships of arthropods and other animals?
Current available fossils post-date the separation of the major animal phyla, or are too enigmatic to really tell us...
... but careful analysis can yield useful information.
end of part one ...
Arthropod origins and relationships
Three main questions:
1. Is Arthropoda a monophyletic group?
2. Which non-arthropod groups are most
closely related to Arthropoda?
3. What are the relationships among
different arthropod groups?
Which non-arthropod groups are most closely related to Panarthropoda?
“lobopod” intermediate
?
ARTICULATA hypothesis: ARTHROPODA plus ANNELIDA
Which non-arthropod groups are most closely related to Panarthropoda?
“lobopod” intermediate
Some of the arthropod “defining” characters are SHARED with ANNELIDA (ragworms, earthworms, leeches and allies)
SegmentedAppendages @ one per segmentCNS with ventral cords and segmental gangliaDorsal tubular heart4 or 5 bands of longditudinal musclesOntogeny of segments (teloblastic)
including engrailed expression? Coelomic cavity origins/development
ARTICULATA hypothesis: ARTHROPODA plus ANNELIDA
Which non-arthropod groups are most closely related to Panarthropoda?
This hypothesis groups Arthropoda with Annelida and Mollusca
Annelida+Panarthropoda = ARTICULATAArticulata+Mollusca+others = PROTOSTOMIAProtostomia+Deuterostomia= COELOMATA
Coelomata/Pseudocoelomatahypothesis of metazoanrelationships
BUT Arthropods differ from Annelids in important ways
• Annelids do not moult
BUT Arthropods differ from Annelids in important ways
• Annelids do not moult• Arthropods and Annelids have very different larval stages
Trochophore Nauplius
?
BUT Arthropods differ from Annelids in important ways
• Annelids do not moult• Arthropods and Annelids have very different larval stages• The arthropod body cavity is a haemocoel, while Annelid body cavities are coelomic compartments
Careful selection of data yielded a very different hypothesis
Initial analyses of single genes yielded phylogenies congruent with Coelomata-Pseudocoelomata
Aguinaldo AMA, Turbeville JM, Linford LS, Rivera MC, Garey JR et al.: Evidence for a clade of nematodes, arthropods and other moulting animals. Nature 1997; 387: 489-493.
Adoutte A, Balavoine G, Lartillot N, Lespinet O, Prud'homme B et al.: The new animal phylogeny: reliability and implications. Proc Natl Acad Sci USA 2000; 97: 4453-4456.
Which non-arthropod groups are most closely related to Panarthropoda?
Using all the orthologous genes from
animals that have had their whole genomes
sequenced supports
Nematoda as a sister to (Arthropoda +
Chordata)
Which non-arthropod groups are most closely related to Panarthropoda?
...but using data derived
from expressed sequence tags
(“partial genomes”) rejects
Coelomata in favour of
Lophotrochozoa–Ecdysozoa–
DeuterostomiaPhilippe H, Lartillot N, Brinkmann H: Multigene analyses of bilaterian animals corroborate the monophyly of Ecdysozoa, Lophotrochozoa and Protostomia. Mol Biol Evol 2005.
Jones M, Blaxter M: Evolutionary biology: animal roots and shoots. Nature 2005; 434: 1076-1077.
This hypothesis groups Arthropoda with Nematoda
Nematoda+Panarthropoda = ECDYSOZOAAnnelida+Mollusca+... = LOPHOTROCHOZOAEcdysozoa+Lophotrochozoa = PROTOSTOMIA
Ecdysozoa-Lophotrochozoa-Deuterostomiahypothesis of metazoanrelationships
Priapulida
TardigradaOnychophora
KinorhynchaGastrotricha
Loricifera
Nematoda
Nematomorpha
Which non-arthropod groups are most closely related to Panarthropoda?
Morphological characters that link the “Ecdysozoa”
• moulting (ecdysone controlled in Arthropoda; mechnisms still unknown, but not simply ecdysone in other taxa)
• lack of cilia (except in neural structures and some sperm)
• triradiate pharynx (Nematoda, Onychophora, Tardigrada, and Pycnogonida within Arthropoda)
Pycnogonum littorale (from South Queensferry)
What are the relationships among different arthropod groups?
What are the relationships among different arthropod groups?
The three possible trees for the four extant Subphyla of Arthropods
What are the relationships among different arthropod groups?
Each tree can be rooted in one of five places...
What are the relationships among different arthropod groups?
Eurypterid
Limulus, horseshoe crab
Chelicerata may be the most ancient arthropod group...
If we believe/suspect/have data to showthat Chelicerata are basal, then we again havea choice of three possible trees...
What are the relationships among different arthropod groups?
Hypotheses based on morphology group Hexapoda with Myriapoda in a clade Uniramia
What are the relationships among different arthropod groups?
Evidence:• tracheal gas exchange system• uniramous appendages• Malphigian tubules• loss of 2nd antennae• loss of mandibular palps
Hypotheses based on morphology group Hexapoda with Myriapoda in a clade Uniramia. Crustacea have been grouped with the Uniramians as Mandibulata
HexapodaMyriapoda
Onychophoraa
Crustacea
Trilobita
Chelicerata
Mandiblulata
The ‘mandibulate theory’
What are the relationships among different arthropod groups?
Hypotheses based on morphology group Hexapoda with Myriapoda in a clade Uniramia. An alternate view places Crustacea closer to Chelicerata: the TCC clade.
HexapodaMyriapoda
Onychophoraa
Crustacea
Trilobita
Chelicerata
The ‘TCC hypothesis’
TCCclade
What are the relationships among different arthropod groups?
Sequence analyses and developmental evidence• strongly link Crustacea and Hexapoda• suggest that similarities between
Hexapoda and Myriapoda are the result of convergence
What are the relationships among different arthropod groups?
For example, the ommatidia of Hexapoda and Crustacea have a shared tetrapartite crystalline cone, while other Arthropoda have either fused ocelli (Myriapoda) or a very different anatomy (Xiphosura, Chelicerata)
Sequence and developmental evidence• strongly links Crustacea and Hexapoda• suggests that similarities between
Hexapoda and Myriapoda are the result of convergence
Hexapoda
Myriapoda
Onychophora
Crustacea
Chelicerata
What are the relationships among different arthropod groups?
What are the relationships among different arthropod groups?
There is still disagreement on the relationship of Hexapoda/Crustacea to the other subphyla
Hwang UW, Friedrich M, Tautz D, Park CJ, Kim W: Mitochondrial protein phylogeny joins myriapods with chelicerates. Nature 2001; 413: 154-157.
Giribet G, Edgecombe GD, Wheeler WC: Arthropod phylogeny based on eight molecular loci and morphology. Nature 2001; 413: 157-161.
Analysis of complete mitochondrial genomes suggests that Hexapoda and Crustacea may be “mutually paraphyletic”
What are the relationships among different arthropod groups?
Nardi F, Spinsanti G, Boore JL, Carapelli A, Dallai R et al.: Hexapod origins: monophyletic or paraphyletic? Science 2003; 299: 1887-1889.
Indeed, the presence in lagerstätten fossils of many varied “crustaceomorph” animals suggests to some that all extant arthropod groups may be derived from a “protocrustacean” ancestor
What are the relationships among different arthropod groups?
Emergence onto land....
Emergence onto land: The Rhynie Chert
pterygote Insecta
Crustacea
Arachnida, ...
end of part two ...
here is a summary:
Arthropod Origins
• There were many early experimentations in arthropod design that may (or may not!) represent early members of extant major groups.
Arthropod Origins
• There were many early experimentations in arthropod design that may (or may not!) represent early members of extant major groups.• In the past, serious arguments were made for multiple independent events of evolution of the arthropod state. eg Manton’s Chelicerates, Crustacea, and Insects/Myriapods.
Arthropod Origins
• There were many early experimentations in arthropod design that may (or may not!) represent early members of extant major groups.• In the past, serious arguments were made for multiple independent events of evolution of the arthropod state. eg Manton’s Chelicerates, Crustacea, and Insects/Myriapods.• However, current developmental evidence and molecular phylogenetic analyses strongly support monophyly.
Arthropod Origins
• There were many early experimentations in arthropod design that may (or may not!) represent early members of extant major groups.• In the past, serious arguments were made for multiple independent events of evolution of the arthropod state. eg Manton’s Chelicerates, Crustacea, and Insects/Myriapods.• However, current developmental evidence and molecular phylogenetic analyses strongly support monophyly.• The ancestor was once thought to be close to annelids (the “Articulata” hypothesis), but ...
Arthropod Origins
• There were many early experimentations in arthropod design that may (or may not!) represent early members of extant major groups.• In the past, serious arguments were made for multiple independent events of evolution of the arthropod state. eg Manton’s Chelicerates, Crustacea, and Insects/Myriapods.• However, current developmental evidence and molecular phylogenetic analyses strongly support monophyly.• The ancestor was once thought to be close to annelids (the “Articulata” hypothesis), but ...• Modern analyses place Arthropoda within the Ecdysozoa, implying that segmentation may have evolved more than once.
Arthropod Origins
• The common ancestor of all Arthropods was probably a ‘lobopod’, similar to extant Onychophora
Arthropod Origins
• The common ancestor of all Arthropods was probably a ‘lobopod’, similar to extant Onychophora• The Chelicerates, Crustaceans, Myriapods and Trilobites all evolved in the sea. The first three groups invaded the land independently.
Arthropod Origins
• The common ancestor of all Arthropods was probably a ‘lobopod’, similar to extant Onychophora• The Chelicerata, Crustacea, Myriapoda and Trilobites all evolved in the sea. The first three groups invaded the land independently.• Hexapoda appear to have evolved from crustacean ancestors, and Collembola may have an independent origin from other Hexapoda
Arthropod Origins
• The common ancestor of all Arthropods was probably a ‘lobopod’, similar to extant Onychophorans• The Chelicerata, Crustacea, Myriapoda and Trilobites all evolved in the sea. The first three groups invaded the land independently.• Hexapoda appear to have evolved from crustacean ancestors, and Collembola may have an independent origin from other Hexapoda• Some of the similarities among these groups are the results of convergent adaptation to terrestrial life, e.g.
• tracheal breathing systems in insects, millipedes and some spiders• malpighian tubule excretory systems in insects and millipedes.• uniramous legs in Myriapoda and Hexapoda• loss of the second antennae in Myriapoda and Hexapoda
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