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

Where we are going and where we have been…

•Previous lecture: •31: Deuterosomes I: Echinoderms &

Hemichordates

•Current Lecture: •32: Deuterosomes II: Chordates

•Next Lecture: •33: Deuterosomes III: Chordates II

Animal Diversity

Diploblasts

Triploblasts

Monoblasts

Triploblasts

Protostomes

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

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

Chordates

Echinoderms

Hemichordates

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

bulacrarians

Focus on Chordates

Deuterostomes

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

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

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

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Focus on Chordates

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Three Major Groups *Lancelets *Tunicates *Vertebrates

Lancelets (aka Cephalochordates)

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Focus on Lancelets

Lancelet development

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016 24

Branchiostoma lanceolatum

TailAnusDorsal hollow nerve cord

NotochordPharyngeal slits

Lancelet Has Key Chordate Features

Branchiostoma lanceolatum

TailAnusDorsal 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

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Focus on Tunicates

Adult Tunicates

• 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

• Solitary tunicates seem to lack all of the synapomorphies of chordates?

• No dorsal hollow nerve cord, no notochord, no postanal tail

Adult Tunicates

• 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

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

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

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

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

Lissoclinum & relatives have cyanobacteria symbionts

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

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

Clicker

A. Annelids

B. Cnidarians C. Protostomes

D. Chordates

E. All of the above

Clicker

A. Annelids (Tubeworms)

B. Cnidarians (Coral) C. Protostomes (Tubeworms)

D. Chordates (Tunicates)

E. All of the above

Filled with Bacteria

52Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016

Basic Tubeworm AnatomyDr. 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!!

Trophosome

Coral Symbiosis with Dinoflagellates

Corals contain symbiotic dinoflagellates (algae) called zooxanthellae

Other Examples?

Other Types of Mutualisms in Animals?

Filarial Nematodes Permanently House Wolbachia

Vertebrate Origins

Ciliated larvae

bulacrariansC

hordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Vertebrates

Vertebral column, anterior skull, large brain, ventral heart

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.

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.

Jawless Fishes (hagfish and lampreys)

Sister group for all other vertebrates

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.

Hagfish not quite full vertebrates

Photo 33.18 Pacific hagfish (Eptatretus stouti).

• https://youtu.be/bqk0mnMgwUQ

You’ve Been Slimed

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

• 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.

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