2007-2008

DomainBacteria

DomainArchaea

DomainEukarya

Common ancestor

Kingdom: AnimalsDomain Eukarya

(Ch. 32, 33, 34)

Introduction to Animal Evolution

Chapter 32

General Features of Animals

• Heterotrophs

• Mobility

• Multicellularity

• Diploidy

• Sexual Reproduction

• Absence of cell wall

• Blastula Formation

• Tissues

Animals probably evolved from colonial protists: A choanoflagellate colony

One hypothesis for the origin of animals from a flagellated protist

Heterotrophs

• Animals cannot make their own food

Mobility

• Animals can perform rapid, complex movements

Multicellularity

• All animals are multicellular

Diploidy

• Most animals are diploid.

Sexual Reproduction

• Most animals reproduce sexually by producing gametes.

Absence of a Cell Wall

• Animals lack rigid cell walls.

Blastula Formation

• The zygote divides and forms a hollow ball of cells.

Early Embryonic Development

Protostomes & Deuterostomes

Body Cavityectoderm

ectoderm

mesodermendoderm

ectodermmesoderm

endoderm

mesodermendoderm

acoelomate

pseudocoelomate

coelomate

coelom cavity

pseudocoel

• Space for organ system development– increase digestive &

reproductive systems

• Coelom– mesoderm & endoderm

interact during development

– allows complex structures to develop• ex. stomach

protostome vs. deuterostome

Body Symmetry

• Radial Symmetry – Parts arranged around a central axis.

• Bilateral – Right and left half.

• Asymmetrical – No symmetry

Tissues & Organs

• Cells are organized by structure and function into:

– Tissues – groups of cells• Muscle tissue, blood, connective tissue

– Organs – groups of tissues• Heart, Lungs, Liver

Origin of Tissues

Segmentation

• Advanced animals are segmented.

Porifera

Cnidaria

Platyhelminthes

sponges jellyfish flatworms roundworms

Nematoda

Mollusca Arthropoda Chordata

Annelida Echinodermata

mollusks

multicellularity

Ancestral Protist

tissues

bilateral symmetry

body cavity

segmentation

Animal Evolution

coelom

starfish vertebrates

endoskeleton

segmentedworms

insectsspiders

backbone

specialization & body complexity

specialized structure & function,muscle & nerve tissue

distinct body plan; cephalization

body complexity digestive & repro sys

digestive sys

body size

redundancy,specialization, mobility

body & brain size, mobility

radial

bilateral

Cambrian Explosion

• Many phyla evolved rapidly over a 40 million year period

• Produced high diversity

• Makes sorting out phylogenetic tree difficult

“Evo-Devo”: Reasons for Cambrian Diversification

• Ecological – Emergence of predator-prey relationships– Evolution of protective outer covering & other

adaptations

• Geological– Enough atmospheric oxygen to support

metabolism

• Genetic– Hox genes- spatial and temporal expression

in developing embryos

Invertebrate: Porifera

• Sponges– no distinct tissues/organs

• A few specialized cell types

– no symmetry– sessile (as adults)

food taken into each cell by endocytosis

Invertebrate: Cnidaria• Jellyfish, hydra, sea anemone, coral

– tissues, but no organs– two cell layers– radial symmetry– predators

• tentacles surround gut opening

• extracellular digestion– release enzymes

into gut cavity– absorption by cells

lining gut

medusapolyp

Stinging cells of Cnidarians

Obviously, we have a movie

Jellyfish Video

Invertebrate: Platyhelminthes

ectoderm

mesoderm

endoderm

• Flatworms– tapeworm, planaria– mostly parasitic– bilaterally symmetrical

• right & left, head (anterior) end

& posterior end – cephalization = development of brain– concentration of sense organs in head

• increased specialization in body plan

Animals nowface the world

head on!

acoelomate

Invertebrate: Nematoda• Roundworms

– bilaterally symmetrical– body cavity

• pseudocoelom = simple body cavity• digestive system

– tube running through length of body (mouth to anus)– many are parasitic

• hookworm

C. elegans

Invertebrate: Mollusca• Mollusks

– slugs, snails, clams, squid– bilaterally symmetrical (with exceptions)– soft bodies, protected by hard shells (mostly)– true coelem

• increases complexity & specialization of internal organs

Invertebrate: Annelida• Segmented worms

– earthworms, leeches– segments

• increase mobility• redundancy in body sections

– bilaterally symmetrical– true coelem

fan worm leech

Invertebrate: Arthropoda• Spiders, insects, crustaceans

– most successful animal phylum– bilaterally symmetrical– segmented

• specialized segments• allows jointed appendages

– exoskeleton• chitin + protein

Arthropod groups

insects6 legs, 3 body parts

crustaceansgills, 2 pairs antennaecrab, lobster, barnacles, shrmp

arachnids8 legs, 2 body partsspiders, ticks, scorpions

Invertebrate: Echinodermata• Seastars, sea urchins, sea cucumber

– radially symmetrical as adults– spiny endoskeleton– Deuterostome– coelom loss of bilateral symmetry?

Invertebrate quick check…

• Which group includes snails, clams, and squid?• Which group is the sponges?• Which are the flatworms?

…segmented worms?…roundworms?

• Which group has jointed appendages & an exoskeleton?

• Which two groups have radial symmetry?• What is the adaptive advantage of bilateral symmetry?• Which group has no symmetry?

Invertebrates: Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda, Echinodermata

• Vertebrates– fish, amphibians, reptiles, birds, mammals– internal bony skeleton

• backbone encasing spinal column

• skull-encased brain

– deuterostome

postanaltail notochord

hollow dorsalnerve cord

pharyngealpouches

Chordata

becomes brain & spinal cord

becomes vertebrae

becomes gills or Eustachian tube

becomes tail or tailbone

Oh, look…your first

baby picture!

Vertebrates: Fish

salmon, trout, sharks

450 mya450 mya

• Characteristics – body structure

• bony & cartilaginous skeleton• jaws & paired appendages (fins)• scales

– body function• gills for gas exchange• two-chambered heart; single loop circulation• ectothermic

– reproduction• external fertilization• external development in egg

gillsbody

Transition to Land

Evolution of tetrapods

Tibia

Femur

Fibula

Humerus Shoulder

RadiusUlna

Tibia

FemurPelvis

Fibula Lobe-finned fish

Humerus

Shoulder

Radius

Ulna

Pelvis

Early amphibian

lung

buccalcavity

glottisclosed

Vertebrates: Amphibians• Characteristics

– body structure• legs (tetrapods)• moist skin

– body function• lungs (positive pressure) & skin for gas exchange• three-chambered heart; 2-loop circulation• ectothermic

– reproduction• external fertilization• external development in aquatic egg• metamorphosis (tadpole to adult)

frogssalamanders toads

350 mya350 mya

Vertebrates: Reptiles250 mya250 mya dinosaurs, turtles lizards, snakesalligators, crocodile

embryoleatheryshell

chorion

allantoisyolk sac

amnion

Vertebrates: Birds (Aves)

• Characteristics – body structure

• feathers & wings• thin, hollow bones

– body function• very efficient lungs & air sacs• four-chambered heart• endothermic

– reproduction• internal fertilization• external development in

amniotic egg• parental care

150 mya150 mya finches, hawk ostrich, turkey

trachea

anteriorair sacs

lung

posteriorair sacs

• Characteristics – body structure

• hair• specialized teeth

– body function• lungs, diaphragm; negative pressure• four-chambered heart• endotherms

– reproduction• internal fertilization• mammary glands make milk• parental care

Vertebrates: Mammals220 mya / 65 mya220 mya / 65 mya mice, ferret

elephants, batswhales, humans

Mammals• 220 million years ago –

evolved from therapsids

• 3 types:– Placental

• Young develop within placenta

– Marsupials• Young are born and then

develop further in the mothers pouch

– Monotremes• Lay eggs

Placental(Human)

Monotreme(Duck-billed Platypus)

Marsupial(Koala)

Vertebrate quick check…

• Which vertebrates lay eggs with shells?

• Which vertebrates are covered with scales?

• What adaptations do birds have for flying?

• What kind of symmetry do all vertebrates have?

• Which vertebrates are ectothermic and which are endothermic

• Why must amphibians live near water?

• What reproductive adaptations made mammals very successful?

• What characteristics distinguish the 3 sub-groups of mammals?

That’s the buzz!

AnyQuestions?