1/9/2013 Topic 3: Evolution & Diversity of What are the protochordates? Vertebrates

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1/9/2013
Topic 3: Evolution & Diversity of
Vertebrates
What are the protochordates?
Protostomes
What are the protochordates?
A phylogenetic perspective
Relationship to craniates
What are the key characteristics of
chordates?
What are the main Protochordate
clades?
What are the differences between
craniates and vertebrates?
Deuterostomes
Hemichordata
Chordata
Protochordates are
______________
Hemichordata
Echinoderms
Pterobranchia
Enteropneusta
Urochordata
Cephalochordata
Pterobranchia
Enteropneusta –
acorn worms
Urochordata
Cephalochordata
Tunicates
Lancelets
Craniata
Modified: Liem et al. 2001, Fig. 2-1
What are the protochordates?
Protostomes
Protostomes
Echinoderms
Urochordata
Cephalochordata
Craniata
Modified: Liem et al. 2001, Fig. 2-1
What sort of
phylogenetic group
are protochordates?
Pterobranchia
What does this
mean?
________________
________________
________________
________________
Enteropneusta
Echinoderms
Urochordata
Cephalochordata
Deuterostomes
Hemichordata
Chordata
Enteropneusta
Deuterostomes
Hemichordata
Chordata
Pterobranchia
What are the protochordates?
What insights might the
study of protochordates
give us?
Craniata
Modified: Liem et al. 2001, Fig. 2-1
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What are the key chordate characteristics?
To understand the
evolution of chordates,
we need an
understanding of what
makes up a chordate
Hemichordates have
some of these
Chordates have all of
these
5 key chordate
characteristics:
1.
2.
3.
4.
5.
1. _______________________
___________________
___________________
___________________
___________________
___________________
2
What are the key chordate characteristics?
Develops by invagination
Results in a neural tube
Develops from ectoderm,
like the epidermis
Becomes the spinal cord
Ventral and solid
in many nonchordates
1
1
3
5
4
Photo © C Arenz
What are the key chordate characteristics?
2. _____________________
What are the key chordate characteristics?
2. Notochord
Also dorsal in position,
ventral to the nerve cord
Develops from mesoderm,
like muscles and skeleton
Is a ___________________
Liem et al. 2001, Fig 2-9;
Nature 2002; C Arenz
Skeletal/support function
Reduced and replaced by
vertebrae in vertebrates
Intervertebral discs
Cells in fluid in a tough
connective tissue sheath
Allows flexion
Resists compression
Maintains body shape
2
2
Liem et al. 2001, Fig 2-9;
Kardong 1998 Fig 2-5
A Harris; A Morton; Univ Maryland
What are the key chordate characteristics?
3. ____________________
What are the key chordate characteristics?
3. Perforated pharynx - function
Anterior end of gut
Develops from endoderm,
like the rest of the gut
Allows ____________ of
water for food particles
Protochordates
Fishes
Primarily _______ (filtration)
___________ (gills, gill slits)
Also in suction ___________
Tetrapods
Slits disappear
Pharyngeal structures
contribute to jaws, ear bones,
endocrine glands…
3
Liem et al. 2001, Fig 2-8D; C Arenz
Photos © U Gille; C Arenz
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What are the key chordate characteristics?
4. _________________
5. ____________
Seems intuitive
What are the key chordate characteristics?
Develops from endoderm
A ciliated groove at the
ventral end of the pharynx
_________________
We define a “tail” this way
Some animals have a tail-like
structure with a gut inside
Often has a ______________
Traps food particles
Cilia move mucous
posteriorly
Transport mucous
food to the
for digestion
and
gut
5
4
Photos © M Himemiya; C Arenz
Liem et al. 2001, Fig 2-8B; C Arenz
What are the key chordate characteristics?
What are the protochordate clades?
Pterobranchia
Controversial
Enteropneusta
Evidence for homology
Urochordata
Cephalochordata
5
Chordata
Position
Endostyle of larval lamprey
metamorphoses into adult
thyroid
Both structures associated
with iodine
Tunicate (Urochordate)
endostyle has similar genes
expressed as a thyroid gland
Protochordates
Homologous to the thyroid
gland in vertebrates
Hemichordata
5. ________________
Craniata
Ogasawara & Satou 2003; C Arenz
What are the
protochordate clades?
________________
Pterobranchia
Enteropneusta (acorn
worms)
~100 species
Modified: Liem et al. 2001, Fig. 2-1
What are the protochordate clades?
Pterobranchia
Filter feeders
Highly specialized
morphology
All are ___________
All are ___________
Pterobranchs are
colonial, deepsea,
and secrete a tube
Acorn worms are
shallower and
fossorial
Photos © Discovery Channel, A Artour, E Balser
Liem et al. 2001, Fig 2-2; Sinauer Associates, 2001
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What are the protochordate clades?
Enteropneusta
What are the protochordate clades?
Enteropneusta
Locomotion
More generalized
Worm-like
______________
Mucous is used to
trap food on ________
Cilia then transport
the food and mucous
into the mouth
Have some chordate
characteristics
Liem et al. 2001, Fig 2-3
____________________
What are the
protochordate clades?
Chordates
___________ (tunicates)
What does this tell you?
All are marine
__________________
Pharyngeal slits
Dorsal, hollow nerve
cord formed by
invagination
Liem et al. 2001, Fig 2-3
What are the
protochordate clades?
Anchoring with collar
Probing with proboscis
Pulling body along
No notochord
Have all chordate
characteristics at some
point in life cycle
Larva
Dorsal hollow nerve cord
Notochord
Pharynx with slits is
rudimentary, not used
Post-anal tail
Endostyle is rudimentary
Pelagic, mobile
Non-feeding
Finds a place to settle
__________________
Sessile, attached to
substrate
Filter feeding
Covered in tough tunic
Photos © C Arenz, I Frank, I Sayers, USGS
Liem et al. 2001, Fig 2-7, C Arenz
What are the
protochordate clades?
Urochordata (tunicates)
Have all chordate characteristics at
some point in life cycle
Adult
_____________________
_____________________
Other characteristics are lost due to
sessile nature
What are the protochordate clades?
_________________
Liem et al. 2001, Fig 2-6, N Hobgood
Future anus near
excurrent siphon
Also chordates
Ciliated neurula larva
Filter feeding,
burrowing adult
Both stages are motile
Lancelets/Amphioxus
~45 species
Liem et al. 2001, Fig 2-10; C Arenz
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What are the differences between
craniates and vertebrates?
What are the protochordate clades?
Dorsal Hollow Nerve Cord
__________________
Pterobranchia
Enteropneusta
Urochordata
Endostyle
Perforated Pharynx
Cephalochordata
Chordata
Post-anal Tail
Protochordates
Notochord
All chordate characteristics
Feeding:
Wheel organ and velar
tentacles create current
Endostyle secretes
mucous
Pharynx filters out food
Water exits through
atriopore
Hemichordata
Craniata
Modified: Liem et al. 2001, Fig. 2-1
Liem et al. 2001, Fig 2-8B; C Arenz
What are the differences between
craniates and vertebrates?
Myxiniformes
(Hagfishes)
Petromyzontiformes
(Lampreys)
Gnathostomata
Amniotes
Modified: Liem et al. 2001, Fig. 3-1
Tetrapoda
Amphbians
Craniata
Vertebrata
Dipnoi (Lungfishes)
_______________
Chondrichthyes
(Sharks and Rays)
Actinopterygii
(Ray-Finned Fishes)
Craniata and
Vertebrata
What are the differences between
craniates and vertebrates?
Which is more
inclusive?
What are hagfishes?
What are lampreys?
Both are highly
specialized parasites
of fishes
Hagfishes
Tear parts off dead and
dying fishes
Use clamping mouth parts
Use a knot behavior to
gain leverage
Little is known about them
Non-vertebrate craniates
Cartilaginous brain case
No vertebrae
Segmental muscles, like
amphioxus and vertebrates
Photo © C Ortlepp
What are the differences between
craniates and vertebrates?
____________________
Lampreys
___________________
Freshwater larvae
Marine adults
Feed on fish body fluids
Rasping mouth parts
Basal vertebrates
Cartilaginous brain case
Cartilaginous arcualia
Arcualia
Notochord
Photos © U Thomas, EPA, Tree of Life
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An Evolutionary Perspective
Pterobranchs
Allows us to consider the
evolution of many
structures
Enteropneusts
Cephalochordates
Lampreys
Other
Vertebrates
Chordata
Hagfishes
Craniata
Vertebrata
1. Pharyngeal slits
2. Dorsal hollow
nerve cord
3. Notochord
4. Post-anal tail
5. Endostyle
6. Segmentation
7. Brain case
8. Vertebrae (arcualia)
Urochordates
Protochordates
Protochordates allow us to study
the evolution of vertebrates
Hemichorata
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Myxiniformes
Craniates and
Vertebrates
Petromyzontif.
Chondrichthyes
Actinopterygii
Vertebrates are very
diverse and the focus
of this course
Some major
nested groups:
____________
_____________
Sarcopterygii
___________
_________
Diapsida
Archosauria
Mammalia
Actinistia
Dipnoi
Lissamphibia
Testudines
Lepidosauria
Crocodylia
Aves
Monotremata
Metatheria
Eutheria
Liem et al. 2001, Fig 3-1
Craniates and Vertebrates
Morphological diversity will be
one course focus
Also appreciate the species
richness:
~48,000 Vertebrates
~25,000 are Fishes
~4,000 Amphibians
~15,000 Reptiles
~6,000 Crocs,
Turtles, Lepidosauria
~9,000 Birds
~4,000 Mammals
5 Hominids
Vertebrate Life, Fig. 1-1
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