BIS2C: Lecture 32 - Deuterosomes II: Chordates

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016
Lecture 32:
Deuterosomes II:
Chordates
BIS 002C
Biodiversity & the Tree of Life
Spring 2016
Prof. Jonathan Eisen
2

Where we are going and where we have been…
3
•Previous lecture:
•31: Deuterosomes I: Echinoderms &
Hemichordates
•Current Lecture:
•32: Deuterosomes II: Chordates
•Next Lecture:
•33: Deuterosomes III: Chordates II

Animal Diversity
4
Diploblasts
Triploblasts
Monoblasts

Triploblasts
5
Triploblasts

Protostomes
6

Clicker
What evidence is consistent with
echinoderms being deuterostomes?
A. Molecular phylogenetics
B. Blastopore developing into anus
C. Presence of bilateral symmetry
D. All of A-C
E. None of A-C
7

Clicker
What evidence is consistent with
echinoderms being deuterostomes?
A. Molecular phylogenetics
B. Blastopore developing into anus
C. Presence of bilateral symmetry
D. All of A-C
E. None of A-C
8

Chordates
9
Echinoderms
Hemichordates
Chordates

Chordates
10
Chordates
Common
ancestor
(bilaterally
symmetrical,
pharyngeal
slits
present)
Echinoderms
Hemichordates
Lancelets
Tunicates
VertebratesVertebral column, anterior skull,
large brain, ventral heart
Notochord,
dorsal hollow
nerve cord,
post-anal tail
Radial symmetry as adults,
calcified internal plates,
loss of pharyngeal slits
Ciliated
larvae
Ambulacrarians
Focus on Chordates

Deuterostomes
11

Chordate Derived Traits Most Apparent in Juveniles
!12Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016

Notochord
• Notochord is a dorsal supporting rod.
• Core of large cells with fluid-filled vacuoles, making it rigid but
flexible.
• In tunicates it is lost during metamorphosis to the adult stage.
• In vertebrates it is replaced by skeletal structures.

Dorsal hollow nerve cord
• Formed by an embryonic folding of the ectoderm
• Develops to form the central nervous system in vertebrates

Post Anal Tail
• Extension of the body past the anal opening
• In some species (e.g., humans) most visible in embryos
• The combination of postanal tail, notochord, and muscles
provides propulsion

Pharyngeal Slits
• The pharynx is a muscular organ that brings water in through
the mouth (via cilia) which then passes through a series of
openings to the outside (slits).
• Ancestral pharyngeal slits present at some developmental
stage; often lost or modified in adults.
• Supported by pharyngeal arches.

Clicker
17
Why are pharyngeal slits NOT considered a
synapomorphy (shared derived trait) of chordates?
A. They occur in other deuterostomes
B. They are lost in some chordates
C. They are modified into gills in vertebrates
D. They only occur in the embryo of some chordates

Clicker
18
Why are pharyngeal slits NOT considered a
synapomorphy (shared derived trait) of chordates?
A. They occur in other deuterostomes
B. They are lost in some chordates
C. They are modified into gills in vertebrates
D. They only occur in the embryo of some chordates

Figure 33.1 Phylogeny of the Deuterostomes

Chordates
20
Chordates
Common
ancestor
(bilaterally
symmetrical,
pharyngeal
slits
present)
Echinoderms
Hemichordates
Lancelets
Tunicates
Notochord,
dorsal hollow
nerve cord,
post-anal tail
Ciliated
larvae
Ambulacrarians
Focus on Chordates

Chordates
21
Chordates
Common
ancestor
(bilaterally
symmetrical,
pharyngeal
slits
present)
Echinoderms
Hemichordates
Lancelets
Tunicates
Notochord,
dorsal hollow
nerve cord,
post-anal tail
Ciliated
larvae
Ambulacrarians
Three Major Groups
*Lancelets
*Tunicates
*Vertebrates

Lancelets (aka Cephalochordates)
22
Chordates
Common
ancestor
(bilaterally
symmetrical,
pharyngeal
slits
present)
Echinoderms
Hemichordates
Lancelets
Tunicates
Notochord,
dorsal hollow
nerve cord,
post-anal tail
Ciliated
larvae
Ambulacrarians
Focus on Lancelets

Lancelet development
23

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016 24
Branchiostoma lanceolatum
Gut
TailAnus
Dorsal hollow
nerve cord
NotochordPharyngeal
slits
Lancelet Has Key Chordate Features

Branchiostoma lanceolatum
TailAnus
Dorsal hollow
nerve cord
NotochordPharyngeal
slits
Lancelet Features
• Lancelets (aka amphioxus) are very small, less than 5 cm.
• Notochord is retained throughout life.
• Burrow in sand with head protruding; also swim.
• Pharynx is enlarged to form a pharyngeal basket for
filtering prey from the water.
• Fertilization takes place in the water.
• Segmented body muscles

Tunicates
26
Chordates
Common
ancestor
(bilaterally
symmetrical,
pharyngeal
slits
present)
Echinoderms
Hemichordates
Lancelets
Tunicates
Notochord,
dorsal hollow
nerve cord,
post-anal tail
Ciliated
larvae
Ambulacrarians
Focus on Tunicates

Adult Tunicates
27
• Tunicates (sea squirts or ascidians, thaliaceans, and
larvaceans):
• Sea squirts form colonies by budding from a single founder.
Colonies may be meters across.
• Adult body is baglike and enclosed in a “tunic” of proteins
and complex polysaccharides secreted by the epidermis.

Adult Tunicates
28
• Solitary tunicates seem to lack all of the synapomorphies of
chordates?
• No dorsal hollow nerve cord, no notochord, no postanal tail

Adult Tunicates
29
• Solitary tunicates seem to lack all of the synapomorphies of
chordates?
• No dorsal hollow nerve cord, no notochord, no postanal tail
HOW ARE THESE CHORDATES?

Photo 44.18 Developing oocytes of sea squirt (ascidian; chordate) Ciona intestinalis. LM.

Photo 44.19 Sea squirt (primitive chordate, C. intestinalis): free-swimming larva.

Photo 44.20 C. intestinalis: early settled larva on substrate.

Photo 44.21 C. intestinalis: further metamorphosis of early settled larva.

Photo 44.22 C. intestinalis: 36 hours after settlement of larva.

Photo 44.23 C. intestinalis: 4 days after settlement of larva. Features of adult can be seen.

Photo 44.24 C. intestinalis: 7 days after settlement of larva

Photo 44.25 Sea squirt juvenile C. intestinalis. Siphons and other adult features evident.

Juvenile Tunicates
38
Ascidian tunicate larva
• Sea squirt larvae have pharyngeal slits, a hollow nerve cord,
and notochord in the tail region.
• The swimming, tadpolelike larvae suggest a relationship
between tunicates and vertebrates.
• Larvacean tunicates do not undergo the metamorphosis and
retain all of the chordate features.
Larvacean tunicates

• Where have we seen big differences between larval
forms and adult forms?

Symmetry

Symmetry
Larvae
are
bilateral

Tunicate Diversity
• ~2,000 described species, all marine filter-feeders
• Body surrounded by a tunic; a thick cellulose covering
• Mostly sessile, one lineage free-swimming
• Feeding through incurrent and excurrent siphons
Solitary
Colonial
Free-swimming

Tunicate colony Lissoclinum patellum
43

1982
44
http://pubs.acs.org/doi/abs/10.1021/jo00349a002

http://pubs.acs.org/doi/pdf/10.1021/jm00126a034

Lissoclinum & relatives have cyanobacteria symbionts
46
Figure 2.Photosymbiotic ascidians
with tunic spicules. Colonies in
situ and tunic spicules (inset) of
Didemnum molle (A),
Trididemnum miniatum (B),
Lissoclinum patella (C),
Lissoclinum punctatum (D), and
Lissoclinum timorense (E). Tunic
cells contain Prochloron cells in
the tunic of Lissoclinum
punctatum (F). Scale bars = 20
µm.

Lesson …
• If you find a novel biochemical activity in
some animal …
• Most likely it is NOT actually from the
animal
48

Clicker
What groups of animals have we seen to
have autotrophic mutualistic symbionts?
A. Annelids
B. Cnidarians
C. Protostomes
D. Chordates
E. All of the above
49

Clicker
A. Annelids
B. Cnidarians
C. Protostomes
D. Chordates
E. All of the above
50

Clicker
A. Annelids (Tubeworms)
B. Cnidarians (Coral)
C. Protostomes (Tubeworms)
D. Chordates (Tunicates)
E. All of the above
51

Filled with Bacteria
52Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016
Basic Tubeworm Anatomy
Dr. Colleen Cavanaugh used microscopy
techniques in 1981 and discovered billions
of bacterial cells packed inside the
tubeworm’s trophosome.
1011 bacteria per gram of trophosome!!
Plume
Trophosome

Coral Symbiosis with Dinoflagellates
Corals contain symbiotic dinoflagellates (algae) called zooxanthellae

Other Examples?
54

Other Types of Mutualisms in Animals?
55

Filarial Nematodes Permanently House Wolbachia
56

Vertebrate Origins
Ciliated
larvae
AmbulacrariansChordates
Common
ancestor
(bilaterally
symmetrical,
pharyngeal
slits
present)
Echinoderms
Hemichordates
Lancelets
Tunicates
Vertebrates
Vertebral column, anterior skull,
Notochord,
dorsal hollow
nerve cord,
post-anal tail

The Vertebrate Body Plan (not in all …)
Anterior skull
enclosing a large brain
A jointed, dorsal
vertebral column
replaces the
notochord during early
development.
Internal Organs
suspended in a
coelom
Well-developed
circulatory
system driven by
a ventral heart
Rigid Internal Skeleton

Vertebrate Evolution
• The structural features can support large,
active animals.
• Internal skeleton supports an extensive
muscular system that gets oxygen from the
circulatory system and is controlled by the
nervous system.
• These features allowed vertebrates to
diversify widely.
59

Phylogeny of the Living Vertebrates

Vertebrates and Land
• All other deuterostomes are marine.
• Vertebrates probably evolved in the oceans
or estuarine environments during the
Cambrian period.
• They have radiated into marine, freshwater,
terrestrial, and aerial environments.
61

Jawless Fishes (hagfish and lampreys)
62

Sister group for all other vertebrates
63
Hagfish

• Weak circulatory system w/ 3 small hearts, a partial cranium,
no stomach, no jaws
• NO BONE (skeleton is cartilage); no vertebrae.
• Blind and produce large amounts of slime as a defense
• They have a specialized structure to capture prey and tear
up dead organisms.
• Development is direct; adults can change sex from year to
year.
64
Hagfish not quite full vertebrates

Photo 33.18 Pacific hagfish (Eptatretus stouti).

• https://youtu.be/bqk0mnMgwUQ
66

Anterior skull
enclosing a large brain
A jointed, dorsal
vertebral column
replaces the
notochord during early
development.
Internal Organs
suspended in a
coelom
Rigid Internal Skeleton
Well-developed
circulatory
system driven by
a ventral heart
The Vertebrate Body Plan

Lampreys

Lampreys
71
• Complete cranium and cartilaginous vertebrae.
• Complete metamorphosis from filter-feeding larvae
(ammocoetes), which are similar to lancelets.
• No bone, no jaws, but cartilaginous vertebrae are present
• Sucker- like mouth with rasping teeth
• Many species are ectoparasites of fish

Photo 33.17 Anadromous lamprey (Petromyzon marinus); Rhode Island.

BIS2C: Lecture 32 - Deuterosomes II: Chordates

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BIS2C: Lecture 32 - Deuterosomes II: Chordates