bis2c: lecture 29: triploblasts: protostomes: ecdysozoans i

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016

Lecture 29:

Triploblasts: Protostomes:

Ecdysozoans I

BIS 002C Biodiversity & the Tree of Life

Spring 2016

Prof. Jonathan Eisen1

Where we are going and where we have been…

•Previous lecture: •28: Triploblasts: Protostomes:

Lophotrochozonas

•Current Lecture: •29: Triploblasts: Protostomes:

Ecdysozoans I

•Next Lecture: •30: Triploblasts: Protostomes:

Ecdysozoans II

Animal Diversity Topics

• Major Groups

• Diversity within Groups

• Key Features of Groups !Body Plans, Forms and Symmetry !Reproduction and Life Cycles !Mobility !Feeding

• Examples

Ecdysozoa

• Key Features of Ecdysozoa !Molting

• Major Groups

• Key Features of Key Groups

• Focus on !Nematodes !Tardigrades

Animal Diversity

Diploblasts

Triploblasts

Monoblasts

Animal Diversity

Triploblasts

Animal Diversity

Ecdysozoans

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016 10

Ecdysozoan Feature #1: Cuticle and Molting

• Ecdysozoans have a cuticle, secreted by the epidermis.

• For animal to grow, cuticle must be shed, or molted, and replaced with a larger one (a process known as ecdysis).

• Molting evolved ~500 mya, apparently only once. All ecdysozoans have a single common ancestor.

• In some wormlike ecdysozoans, the cuticle is thin and flexible.

• A thin cuticle allows gas and water exchange but restricts animal to moist habitats.

• In arthropods, the cuticle is an exoskeleton, thickened by proteins and chitin, a waterproof polysaccharide.

• The exoskeleton restricts movement and gas exchange; new mechanisms for these functions evolved.

A Few Summaries for Your Enjoyment …

Ecdysozoans

Wormlike Marine Ecdysozoans

Priapulids Kinorhynch Loriciferan

Wormlike Marine Ecdysozoans

• Priapulids: !Unsegmented, three-part body plan !Burrow in soft sediments !Capture prey with a toothed, muscular pharynx that is

everted through the mouth

• Kinorhynchs: !Microscopic !Body has 13 segments, with separate cuticular plates that

are molted !Feed by ingesting sediments through their retractable

proboscis

• Loriciferans: !Minute !Not discovered until 1983 !Body is covered by six plates (lorica = “corset”)

Ecdysozoans

Horsehair Worm Larvae Are Parasitic

Horsehair Worms

• Horsehair worms: very thin; up to a meter in length; most are freshwater.

• Larvae are internal parasites of insects and crayfish.

• Adult has no mouth and a reduced gut. Some may feed only as larvae; others continue to grow and molt, and may be absorbing nutrients from the environment.

Horsehair Worms

• Horsehair worms: very thin; up to a meter in length; most are freshwater.

• Larvae are internal parasites of insects and crayfish.

• Adult has no mouth and a reduced gut. Some may feed only as larvae; others continue to grow and molt, and may be absorbing nutrients from the environment.

• WHATEVER YOU DO - DO NOT - DO NOT GOOGLE “HORSEHAIR WORM VIDEO”

Not Just for Your Enjoyment …

Ecdysozoans

Clicker

Which of the following would make the most sense to add to the UC Davis Department of Nematology and Entomology?

A: Plants

B: Vertebrates

C: Echinoderms D. Annelids

E. Cnidarians28

Clicker

Which of the following would make the most sense to add to the UC Davis Department of Nematology and Entomology?

A: Plants

B: Vertebrates

C: Echinoderms D. Annelids

E. Cnidarians29

Animal Diversity

Ecdysozoans

Nematodes (roundworms)

!32Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016

Name from Greek: nematos (thread) eidos (form)

Thick, multilayered cuticle

Pharynx, a muscular organ at the anterior end, moves materials through the gut.

Gas and nutrient exchange occurs through the cuticle and the gut wall, which is only one cell thick.

Mouthparts modified for specialized tasks

• Extremely abundant and universally distributed.

• >25,000 species described.

• Includes scavengers, parasites, predators

• Many are microscopic; the largest is 9 meters long—a parasite in placentas of female sperm whales.

• Reduced musculature and digestive system (pseudocoelom)

Nematode Features

• Caenorhabitis elegans is used as a model organism in genetics and developmental biology research.

• It is easy to cultivate, matures in three days, and has a fixed number of body cells.

Nematode Example: C. elegans

Clicker

From an evolutionary point of view, which of the following is the best candidate for a model organism to compare with humans

A. C. elegans (Nematode)

B. Fruit fly (Arthropod)

C. Giant squid (Cephalopod) D. Earthworm (Annelid)

E. All are equally good

Clicker

From an evolutionary point of view, which of the following is the best candidate for a model organism to compare with humans

A. C. elegans (Nematode)

B. Fruit fly (Arthropod)

C. Giant squid (Cephalopod) D. Earthworm (Annelid)

E. All are equally good

Animal Diversity

Triploblasts

• Whatever you do DO NOT - I REPEAT DO NOT- GOOGLE - GIANT NEMATODE SLITHERING DEAD SPIDER

Root-Knot Nematodes

• Meloidogynes nematodes infect root systems of plants • The nematodes cause galls where juvenile worms develop

• WARNING THE NEXT FEW SLIDES COULD GROSS PEOPLE OUT

Nematode Example: Filarial Diseases

• Caused by several different parasitic nematodes and transmitted by mosquitoes • Infect lymph nodes, which can then get blocked. This leads to edema (swelling) and other problems.

HOW CAN WE TREAT THESE DISEASES?

Opisthokonts

Shared derived traits of clade?

Anti fungal drugs

50http://www.slideshare.net/drjankiborkar/antifungals-14155209

It’s Always More Complicated III

Humans & Nematodes Much Closer than Humans and Fungi

HumansNematodes

http://www.worldbank.org/en/news/video/2014/06/30/treating-river-blindness-and-other-neglected-tropical-diseases

2015 Nobel Prize in Medicine

But …

Wolbachia

http://www.theatlantic.com/science/archive/2015/10/ivermectin-nobel-drugs-elephantiasis-filariasis-nematodes-wolbachia/409306/

Ed Yong

The avermectins that Campbell and Ōmura discovered, and especially their most potent member ivermectin, can control the symptoms of these diseases by killing the larval nematodes. But they aren’t cures, because they don’t damage the astonishingly sturdy adults. And since these worms can live for a decade, and can release thousands of new larvae every day, their hosts must resign themselves to years of regular treatments.http://www.theatlantic.com/science/archive/2015/10/ivermectin-nobel-drugs-elephantiasis-filariasis-nematodes-wolbachia/409306/

Filarial Nematodes Permanently House Wolbachia

And unfortunately, this means that killing the worms would make everything much worse, because they’d release all their Wolbachia in their death throes. “You get exploding nodules, and scrotal inflammation,” he told me. “You don’t want that. You want to kill the worms slowly, and it’s hard to think how you’d do that with an anti-nematode drug.”

What Would You Use to Kill Wolbachia?

Ecdysozoa

Tardigrades

Tardigrades (aka water bears)

• Fleshy, unjointed legs

• Use a fluid-filled body cavity as a hydrostatic skeleton

• Extremely small

• No circulatory or gas exchange systems

• Live in marine sands and on water films on plants

• When water films dry up, tardigrades lose water and shrink to form a dormant state that can last at least a decade.

• Tardigrades have been found at densities as high as 2 million / m^2 of moss.

Tardigrades

Velvet worm

Onychophorans (velvet worms)

• Live in leaf litter in the humid tropics

• Thin, flexible cuticle

• Use fluid-filled body cavity as a hydrostatic skeleton

• May look similar to arthropod ancestors

Figure 32.19 A Trilobite Fossil

bis2c: lecture 29: triploblasts: protostomes: ecdysozoans i

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bis2c: lecture 30: triploblasts: protostomes: ecdysozoans ii