topic 3: evolution & diversity of what are the … 1 what are the key chordate characteristics?...
TRANSCRIPT
1/9/2013
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Topic 3: Evolution & Diversity of
Vertebrates
� 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?
What are the protochordates?
� Protochordates are ______________
� Hemichordata
� Pterobranchia
� Enteropneusta –acorn worms
� Urochordata
� Tunicates
� Cephalochordata
� Lancelets
Modified: Liem et al. 2001, Fig. 2-1
Protostomes
Echinoderms
Pterobranchia
Enteropneusta
Urochordata
Cephalochordata
Craniata
Chordata
Hemichordata
Deuterostomes
What are the protochordates?
� What sort of phylogenetic group are protochordates?
� What does this mean?
� ________________ ________________
� ________________ ________________
Modified: Liem et al. 2001, Fig. 2-1
Protostomes
Echinoderms
Pterobranchia
Enteropneusta
Urochordata
Cephalochordata
Craniata
Chordata
Hemichordata
Deuterostomes
What are the protochordates?
� What insights might the study of protochordates give us?
Modified: Liem et al. 2001, Fig. 2-1
Protostomes
Echinoderms
Pterobranchia
Enteropneusta
Urochordata
Cephalochordata
Craniata
Chordata
Hemichordata
Deuterostomes
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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. ___________________
Photo © C Arenz
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3
4
5
1. _______________________
� Develops by invagination
� Results in a neural tube
� Develops from ectoderm, like the epidermis
� Becomes the spinal cord
� Ventral and solid in many non-
chordates
Liem et al. 2001, Fig 2-9; Nature 2002; C Arenz
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What are the key chordate characteristics?
2. _____________________
� Also dorsal in position, ventral to the nerve cord
� Develops from mesoderm, like muscles and skeleton
� Is a ___________________
� Cells in fluid in a tough connective tissue sheath
� Allows flexion
� Resists compression
� Maintains body shape
Liem et al. 2001, Fig 2-9; Kardong 1998 Fig 2-5
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What are the key chordate characteristics?
2. Notochord
� Skeletal/support function
� Reduced and replaced by
vertebrae in vertebrates
� Intervertebral discs
A Harris; A Morton; Univ Maryland
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What are the key chordate characteristics?
3. ____________________
� Anterior end of gut
� Develops from endoderm,
like the rest of the gut
� Allows ____________ of
water for food particles
Liem et al. 2001, Fig 2-8D; C Arenz
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What are the key chordate characteristics?
3. Perforated pharynx - function
� Protochordates
� Primarily _______ (filtration)
� Fishes
� ___________ (gills, gill slits)
� Also in suction ___________
� Tetrapods
� Slits disappear
� Pharyngeal structures contribute to jaws, ear bones,
endocrine glands…
Photos © U Gille; C Arenz
What are the key chordate characteristics?
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4. _________________
� Seems intuitive
� We define a “tail” this way
� Some animals have a tail-like structure with a gut inside
� Often has a ______________
Liem et al. 2001, Fig 2-8B; C Arenz
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What are the key chordate characteristics?
5. ____________
� Develops from endoderm
� A ciliated groove at the
ventral end of the pharynx
� _________________
� Traps food particles
� Cilia move mucous
posteriorly
� Transport mucous and food to the gut
for digestion
Photos © M Himemiya; C Arenz
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What are the key chordate characteristics?
5. ________________
� Homologous to the thyroid gland in vertebrates� Controversial
� Evidence for homology
� 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
Ogasawara & Satou 2003; C Arenz
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What are the key chordate characteristics? What are the protochordate clades?
Modified: Liem et al. 2001, Fig. 2-1
Pterobranchia
Enteropneusta
Urochordata
Cephalochordata
Craniata
Chordata
Hemichordata
Protochordates
� ________________� Pterobranchia
� Enteropneusta (acorn worms)
� ~100 species
� 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
What are the
protochordate clades?
� Pterobranchia
� Filter feeders
� Highly specialized
morphology
Liem et al. 2001, Fig 2-2; Sinauer Associates, 2001
What are the protochordate clades?
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Liem et al. 2001, Fig 2-3
What are the protochordate clades?
� Enteropneusta
� More generalized
� Worm-like
� ______________
� Mucous is used to
trap food on ________
� Cilia then transport
the food and mucous into the mouth
� Enteropneusta
� Locomotion
� Anchoring with collar
� Probing with proboscis
� Pulling body along
� No notochord
� Have some chordate characteristics
� Pharyngeal slits
� Dorsal, hollow nerve cord formed by
invagination
Liem et al. 2001, Fig 2-3
What are the protochordate clades?
� ____________________
� Chordates
� What does this tell you?
� All are marine
� __________________
� 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
What are the
protochordate clades?
� ___________ (tunicates)
� 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
� Future anus near
excurrent siphon
� Endostyle is rudimentary
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
Liem et al. 2001, Fig 2-6, N Hobgood
What are the
protochordate clades?
� _________________
� 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
What are the protochordate clades?
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� __________________
� All chordate characteristics
� Feeding:
� Wheel organ and velar tentacles create current
� Endostyle secretes mucous
� Pharynx filters out food
� Water exits through atriopore
Liem et al. 2001, Fig 2-8B; C Arenz
Dorsal Hollow Nerve Cord
Notochord
Perforated Pharynx
Post-anal Tail
Endostyle
What are the protochordate clades?What are the differences between
craniates and vertebrates?
Modified: Liem et al. 2001, Fig. 2-1
Pterobranchia
Enteropneusta
Urochordata
Cephalochordata
Craniata
Chordata
Hemichordata
Protochordates
� Craniata and
Vertebrata
� Which is more inclusive?
� What are hagfishes?
� What are lampreys?
� Both are highly
specialized parasites of fishes
Modified: Liem et al. 2001, Fig. 3-1
Myxiniformes (Hagfishes)
Petromyzontiformes (Lampreys)
Chondrichthyes (Sharks and Rays)
Actinopterygii (Ray-Finned Fishes)
Dipnoi (Lungfishes)
Amphbians
Amniotes
Tetra
poda
Verte
brata
Gnathostomata
Craniata
What are the differences between
craniates and vertebrates?
� _______________
� 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
Photos © U Thomas, EPA, Tree of Life
Notochord
Arcualia
What are the differences between
craniates and vertebrates?
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An Evolutionary Perspective
� Protochordates allow us to study the evolution of vertebrates
� Allows us to consider the evolution of many structures
1. Pharyngeal slits
2. Dorsal hollow nerve cord
3. Notochord
4. Post-anal tail
5. Endostyle
6. Segmentation
7. Brain case
8. Vertebrae (arcualia) Other Vertebrates
Lampreys
Hagfishes
Cephalochordates
Urochordates
Enteropneusts
Pterobranchs
Vertebrata
Craniata
Chordata
Hemichorata
Protochordates
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Craniates and
Vertebrates
� Vertebrates are very diverse and the focus of this course
� Some major nested groups:
� ____________
� _____________
� Sarcopterygii
� ___________
� _________
� Diapsida
� Archosauria
� Mammalia
Liem et al. 2001, Fig 3-1
Myxiniformes
Petromyzontif.
Eutheria
Testudines
Lissamphibia
Dipnoi
Actinistia
Actinopterygii
Chondrichthyes
Metatheria
Monotremata
Aves
Crocodylia
Lepidosauria
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