Download III.4. Animals-I

Lecture III.4. Animals – I.
Molecular-Based Phylogeny of Animalia. Note polytomies (unresolved branching sequences) leading to
sponges and Coelenterates (= Cnidaria+Ctenophera).
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Overview.
 Sister group to choanoflagellates.
 Characteristics include
1. Multicellularity.
A simplified animal phyloge2. Differentiated cells, tis- ny.
sues, organs.
3. Motility at some stage.
4. Heterotrophy.
5. Muscular and neuroSimplified animal phylogeny.
sensory systems.
6. Complex development including blastula formation
(all) and gastrulation (most).
Sponges are basically choanoflagellates embedded in a gelatinous mass strengthened by calcareous / siliceous spicules and /
or a protein called spongin.
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Some Terminology.
 Metazoa – all animals.
 Eumetazoa – all animals excluding sponges and a few
others.
1. Two or three cell layers.
2. Radial or bilateral symmetry.
 Bilateria – all animals excluding sponges, cnidaria and a
few others.
1. Three cell layers.
2. Bilateral symmetry.
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Evolutionary Trends.
 Increasing size and morphological complexity.
 Exploitation of new (benthic / terrestrial) environments.
 Homeostasis – Increasing ability to
1. Perceive, respond to and control conditions of life.
2. Maintain constant internal conditions in the face of external environmental fluctuations.
 Nervous System – Increasing
1. Nervous system complexity. Nerve nets replaced by
CNS
2. Cephalization: concentration of sense organs at the
front of the animal.
3. Intelligence: Behavior; social interaction; cognitive ability; self-awareness.
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Principle Groups.
 Porifiera (sponges)
1. Radial symmetry or none.
2. No cell layers as such.
 Cnidaria (hydra, jellyfish, corals).
1. Radial symmetry.
2. Two cell layers.
 Bilateria
1. Bilateral symmetry.
2. Three cell layers.
 Major Bilaterian Groups.
1. Lophotrochozoans. Include
a. Mollusks – snails, clams, cephalopods.
b. Annelids – segmented worms.
2. Ecdysozoans
a. “Molting animals.”
b. Arthropods and their allies.
3. Deuterostomes
a. Echinoderms – starfish, etc.
b. Chordates – “fish”, tetrapods.
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Phyla Distinguished by Body Plans.
 Symmetry:
1. Radial.
2. Bilateral.
3. Other.
 Number of embryonic cell
(tissue) layers:
1. Two – diploblastic.
2. Three – triploblastic.
 Embryonic cell layers:
1. Endoderm ⇒ lining of
the gut.
2. Mesoderm ⇒ muscles,
connective tissue.
3. Ectoderm ⇒ skin, nervous system.
 Type of body cavity:
1. None.
2. Pseudocoelom.
3. True coelom.
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Pseudocoelomate Locomotion (Round worm).
Coelomate Body Plan (Earthworm).
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Phyla Distinguished by Body Plans (continued).
 Embryonic development.
1. Protostomes.
a. Blastopore becomes the mouth.1
b. Coelom (body cavity) forms within mesoderm.
c. Cleavage spiral in some.
d. Embryonic cell fate determined early.
2. Deuterostomes.
a. Blastopore becomes the anus.
b. Coelom forms from an out-pocketing of the gut.
c. Cleavage radial.
d. Embryonic cell fate determined late.
Germ Layers and Tissues
Ectoderm
Epidermis; nervous system
Muscle, bone, blood and other
Mesoderm
connective tissues
Mucous membranes lining digesEndoderm
tive tract and respiratory system
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In some protostomes both mouth and anus form from the blastopore.
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Development in Protostomes and Deuterostomes.
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Origin of Embryonic Tissue Types.
 Traditional view: Germ layers and gastrulation evolved after sponges (cladogram on page 1).
 More recent suggestion:
1. Beginnings of germ layer differentiation seen in some
sponges.
2. Based on observation of transcription factor GATA
important in regulating endodermal development in
Eumetazoa.
Alternative opinions regarding the origins of germ layers and gastrulation. From Nakanishi et al. (2014); See also Adamska (2016).
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Embryonic Tissues and Autoimmune Disease.
 Antigenic properties of adult
tissue determined by embryonic
tissue of origin.
 Iconic Example: Stevens Johnson Syndrome (SJS).
1. Often fatal auto-immune disorders triggered by drugs
and infections.
2. Antibodies attack epithelial
tissue (skin, cornea, etc.),
i.e., tissue that derives from
ectoderm.
3. Skin dies, sloughs off
4. Dermis largely unaffected –
antigenically distinct; derives SJS survivor after 7 years.
from mesoderm.
5. Sequelae include permanent damage to eyes.
6. But – if patient survives, essentially normal skin often
replaces tissue that was lost.
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Animal Feeding Strategies.
 How
1. Filter feeders.
a. Strain out food particles.
b. Clams; krill (crustaceans); baleen whales.
2. Deposit feeders
a. Eat their way through the environment.
b. Earthworms.
3. Fluid feeders.
a. Suckers and drinkers.
b. Hummingbirds, adult mosquitoes, vampire bats.
4. Mass feeders – bite / tear off chunks - us.
 What
1. Predators: eat other animals.
2. Herbivores: plants.
3. Detritivores/Saprovores: dead/decomposing matter.
4. Omnivores: anything.
 Parasites: live in (endo-) or on (ecto-) living hosts.
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Self-Quiz. Deposit and Filter Feeders. Enter the taxonomic
group (phylogeny on page 1) to which each of the following
examples belongs.
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Self-Quiz (continued). Fluid and Mass Feeders. Enter the
taxonomic group to which each of the following examples
belongs.
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Locomotion.
 Whole body undulates.
1. Nematode – muscles + pseudocoelom.
2. Fish, snakes – muscles + skeleton.
 Limbs for walking, paddling, flying.
1. Sac-like – Onycophorans.
2. Tube feet – echinoderms.
3. Jointed (external skeleton) – arthropods
4. Not jointed (internal skeleton) – vertebrates.
 Are animal limbs homologous?
1. It depends.
2. Often limb development controlled by same genes.
a. But the limbs themselves arose independently.
b. In such cases, genes are homologous, the structures are not.
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Possible phylogeny of genes that control limb development and other
functions in Bilateria (Panganiban and Rubenstein, 2002). Note gene
duplications on the branch leading to vertebrates.
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Figure Next Page. Top. Experimental set-up and results
implicating the importance of Dll (distal-less*) homologs in
animal limb development. Dll itself is a homeobox gene,
the expression of which is necessary for normal limb development in Drosophila. Dll homologs, called Dlx genes,
are expressed in developing limbs in at least six different
phyla. The figure is from your text (4th edition), with the
conclusion suitably modified to reflect the fact that the experiment shows that the genes, but not necessarily the
structures for which they presently code, are homologous.
Not noted in the write-up is the fact that that, while Polychaete worms have leg-like parapodia, other segmented
worms do not, i.e., not all segmented worms have appendages. Bottom. The lancelet, Amphioxus, is close to
the ancestry of vertebrates. While various vertebrate characters (gill slits, notochord, dorsal nerve cord, segmented
trunk musculature) are present, there is no suggestion of
appendages. This argues against the claim that all animal
appendages (as opposed to the genes that control their
development) are homologous; likewise, the fact that
Cambrian chordates (next lecture) also lacked appendages.
________
* In Drosophila, limb development is aborted in Dll mutants.
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Limbs.
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Life Cycles.
 Diplontic (diploid except for
gametes) with a very few exceptions.
 Multiple stages facilitate
1. Dispersal;
2. Exploitation of different
environments, resources.
 Stages can be represented
by different individuals or
the same individual.
 Reproduction.
1. Sexual or asexual.
2. Fertilization internal or
external.
3. Birth – live or from eggs Animal reproduction. Top.
deposited into the envi- Damsel flies mating. Bottom.
Giant clam releasing sperm.
ronment.
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Complete (left) and incomplete metamorphosis (right) in insects. In these cases, the same individual passes through the
different life cycle stages.
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The broad fish tapeworm, Diphyllobothrium latum, has two intermediate hosts through which it must pass before infecting a
fish-eating mammal, the primary host in which it reproduces.
The cycle is completed when the primary host defecates in or
near fresh water. In this case, life cycle stages are represented
by different individuals.
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Simple Animals.
 Sponges – not a monophyletic group – see p. 1.
1. Radial symmetry
asymmetrical.
or
2. Sessile. Support provided by a “skeleton” consisting of spines called
spicules and/or an elastic network of fibers
3. Organized about a series
of water canals (pores).
4.
Water is sucked into the
Specialized collar cells sponge through pores and
exits through the osculum.
(choanocytes)
Currents are generated by
a. Suck water in.
the beating of collar cell flab. Extract food parti- gella.
c.
cles.
Excrete waste products.
5. "Used" water exits through one or more oscula.
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 Cnidaria.
1. Hydras, jellyfish, corals.
a. Two cell layers;
b. Radial symmetry.
c. "Blind" guts.
d. Almost all marine.
2. Carnivorous. Use nematocysts to paralyze prey.
3.
Generalized cnidarian life cyBasic structure a two- cle showing polyp & medusa.
layered, tentacle bearing cup that is either a
polyp (sessile) or a medusa (floating).
4. Life cycle involves both
a. Polyps reproduce by
budding.
b. Medusas reproduce
sexually.
c.
Fertilized eggs develop into ciliated,
free-swimming planNematocyst (here called “cnidula larva.
oblast”) structure.
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5. Three principal groups.
a. Hydrozoans - hydras
(solitary and colonial)
b. Scyphozoans – jellyfish
c.
Anthozoans – anemones (solitary); corals
(colonial)
6. Portuguese man-of-war,
Physalia physalis, is a
floating hydrozoan colony.
a. Consists of differentiated polyps specialized for different functions: flotation (“sail”),
stinging, feeding and
reproduction.
b. Tentacles pack a wal- Top. Portuguese man-of-war
lop.
is a floating hydrozoan colony. Bottom. Victim.
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Planula larvae of a jellyfish (Scyphozoa) are basically ciliated gastrulas.
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 Corals (Anthozoans).
1. Famous for reef formation.
2. Many contain symbiotic photosynthetic dinoflagellates.
3. Accounts for coral’s
a. Ability to live in nutrient
poor waters.
b. Restriction to surface waters.
4. But –
a. Coral reefs often found far
out to sea where they form
ring-like atolls around shallow lagoons.
b. Adjacent waters very deep:
How do atolls form in the
first place?
Three stages in coral reef
3.
formation. From top to botDarwin’s conjectured solu- tom: fringing reef; barrier
tion: balance between sea reef; atoll.
floor subsidence and reef
growth.
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 Ctenophora (comb jellies).
1. Name derives from locomotor organ consisting of eight
comb-like rows of fused plates of cilia called ctenes.
2. Previously grouped with Cnidaria in Coelenterata.
3. Complete gut.
4. Two cell layers separated by a gelatinous mesoglea.
5. Tentacles, but no nematocysts – use sticky filaments.
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Protostomes vs. Deuterostomes.
 Fundamental split among Bilateria.
 Recall developmental differences – see pp. 9-10.
 Both
1. Triploblastic (three cell layers)
2. Have free-floating, ciliated larvae (dispersal stage) that
differ with regard to number and anatomy of cilia.
Left. Protostome larva (annelid) larva. Right. Deuterostome (echinoderm) larva.
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Two Great Groups of Protosomes.
 Lophotrochozoa.
1. Include:
a. Flatworms;
b. Rotifers;
c. Lophophorates (BryLophotrochozoan phylogeny.
ozoans, brachiopods, Only Lophophorates have a
phoronid worms);
lophophore.
d. Spiralians (Nemertean worms, annelids, mollusks).
2. Name derives from lophophore (a feeding organ) +
trochophore larva (previous page).
a. The word lophophore from the Greek - lophos =
'crest of a helmet' + phoros = 'bearing.' Hence,
'crest-bearing.'
b. U-shaped ridges around the mouth bear one or
two rows of hollow, ciliated tentacles – video.
c.
Occur in Lophotrochozoan groups that collectively
form the Lophophorates.
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3. When there is a skeleton (shell), growth by accretion.
Lophotrochozoans. Left. Shell of the pearly nautilus grows by
accretion, Right. A phoronid worm and its lophophore. Below. A
bryozoan extends its lophophore.
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 Ecdysozoa ("Worms”, Lobopods and arthropods).
1. Grow by molting a stiff external skeleton
2. Locomotion often by jointed appendages.
Ecdysozoan phylogeny based principally on molecular data. Four of
the five worm-like phyla – Kinorhyncha, Priapulida, Nematomorpha
and Nematoda – have pseudocoeloms and were formerly grouped together; the fifth, Chaetognatha (arrow worms), was traditionally
grouped with deuterostomes on the basis of embryology. Of the remaining Ecdysozoan phyla, those with jointed appendages are placed
in the phylum Arthropoda, the subphylum Uniramia beiong a fusion
of insects and the myriapodous arthropods – millipedes and centipedes. Tardigrades and onycophorans, sometimes called Lobopods,
are allied to the arthropods with which they share the derived traits of
having appendages for walking and chitinous exoskeletons.
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3. Ecdysozoa shed their "skins" in order to grow.
a. In Lophotrochozoans, the shell is open at one end
of both. Shell grows by accretion.
b. Presence of an exoskeleton makes this impossible. Instead, the animal molts.
4. Arthropods have the most advanced ecdysozoan skeletons – essentially suits of armor.
a. Consist of plates joined by articular membranes;
secreted by underlying hypodermis.
b. At molting, the hypodermis secretes an enzyme that
erodes the base of the overlying cuticle; new cuticle
forms beneath it.
c.
The old cuticle splits, and the animal crawls out.
d. New cuticle soft, pliable – allows animal to grow.
e. Growth stage between molts called instars. Metabolic reserves accumulate between molts.
5. Ecdysozoan monophyly based on molecular evidence
(small ribosomal subunit and other genes).
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Next page. Arthropod exoskeleton (A) consists of overlapping
cuticular plates joined by thin, flexible articular membranes (B)
often folded beneath the plates. Arthropods are primitively segmental, and the cuticle of each segment consists of four primary
plates: a dorsal tergum, two lateral pleura and a ventral sternum. The skeleton of the appendages (C) (primitively one pair
per segment) is similar, with the membranes in some cases supplemented by vertebrate-like condyles. Muscles (inside the
skeleton) attach to sub-cuticular “bumps” called apodemes that
are analogous to vertebrate tendons.
The cuticle is secreted (D) by a single layer of cells called the hypodermis that consists of two layers, a thin outer epicuticle and
the much thicker procuticle beneath it. The procuticle contains
chitin, which in some cases is strengthened by impregnation with
calcium salts. Like vertebrate epithelial tissue, the cuticle derives
from embryonic ectoderm that forms other structures in addition
to the outer covering. In particular, arthropod fore- and hind-guts
are lined with cuticle, as are the respiratory organs and parts of
the reproductive system.
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Uniramians.
 Include insects (three body regions, three pairs of legs attached to the thorax).
 The most successful of all Metazoa. Many have wings.
 “Advanced” traits such as the
ability to maintain constant body “An inordinate fondness
temperatures – some moths and for beetles.”
bees.
Competing hypotheses for the evolutionary origin of wings. Diagrammatic cross sections show (A) the ancestor of winged insects according to the wings-from-legs theory; (B) an extant
winged insect; (C) the ancestor of winged insects according to
the wings from tergal extensions theory. From Jockusch and
Ober (2004).
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 Some social hymenoptera (ants, wasps, bees), have
complex societies with
1. Individuals specialized behaviorally and morphologically for different tasks.
2. Sterile workers.
 Explanations for the evolution of worker sterility include
1. Haplodiploid sex determination (males haploid; females
diploid);
2. Kin selection
3. See HW questions 11-12.
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Questions.
1. (2 pts) Referring to the cladogram on page 1 and with
regard to mono- / polyphyly, vertebrates are ______
group; invertebrates are _______ .
2. (2 pts) Referring to the cladogram on page 1, which of
the following traits arose just once?
a. Coelom
b. Limbs
c. Pseudocoelom
d. Radial symmetry
e. Segmentation
3. (2 pts) Referring to the cladogram on page 1, the acoelomate condition of flatworms is a(n) _____ trait.
4. (2 pts) The mass of cells that results from division of the
original fertilized egg is called a blastula. A ______ results when the blastula invaginates.
5. (2 pts) If all animal limbs really are homologous (as opposed to the genes that control their development),
cephalochordate ancestors must ______ .
6. (4 pts) SJS patients often require intubation. Why? (You
may have to look up “intubation.”)
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7. (4 pts) A general evolutionary trend among animals has
been increased size and complexity. What would Lamarck have had to say about this? What would Darwin
have said?
8. (4 pts) Baleen whales are huge; their prey, tiny. Most
predators that eat small prey are themselves small.
Why?
9. (4 pts) Strategies that have been employed in the fight
against malaria include the following: a. insecticides; b.
draining ponds and marshes; c. anti-malarial drugs; d.
window screens; e. bed nets often impregnated with insecticide. Which of these target(s) the larval stage?
10. (4 pts) The classifications / phylogenies given in this lecture are quite different from those that your instructor
learned way back when. What principal development(s)
might have caused the changes?
11. (8 pts) In many social hymenoptera (ants, bees), workers (all diploid females) are generally sterile. In these
species, males are haploid. From an evolutionary point
of view, how might these observations be related? (Requires outside reading.)
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12. (8 pts) Regarding your answer to #11, how would your
answer be affected by the observation that queens often
mate with multiple males? Likewise, how does sex determination in termites affect your argument? (Requires
outside reading.)
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