Introduction to Animal

Evolution

Chapter 32

Origins

All phyla form rather quickly in the “Precambrian explosion”

Before 500 MYA Common ancestry with fungi in a colonial

protistan similar to a choanoflagellate

Precambrian Explosion

Chaoanoflagellate

Simple colonial Protist

WHAT IS AN ANIMAL?

Animals are multicellular eukaryotes

I’ve got lots of cells and they all have a nucleus

Animals are heterotrophic by ingestion

I just love to ingest.

Store carbohydrate as Glycogen, or convert to fat

Animals have muscle and nervous tissues

Animal cells lack cell walls

I’m all boxed in

Not me

Have special cell to cell connections:

Tight junctions – seals between cells Gap junctions – communication between

cells Desmosomes -anchoring junctions Fig. 6.32 True tissues have these 4 Types of tissues

Animal Tissue types:

Epithelial Muscle Nervous Connective- 3 parts

– Cells, matrix and fibers

Most animals reproduce sexually

Only have 1 lifecycle!!

Mostly all diploid (2n)Except sperm and egg, with a few exceptions (e.g. drone bees etc.)

Asexual reproduction does happen in some lineages, but it is not common (e.g. aphids)

Animals Undergo Embryonic Development

Zygote – first new cell of animal– Diploid– Fertilized egg

Cleavage – – repeated cell division without growth– Same amount of cytoplasm divides into – More, smaller cells

Figure 32.1 Early embryonic development (Layer 1)

Figure 32.1 Early embryonic development (Layer 2)

Animals Undergo Embryonic Development

Blastula – hollow balls of cells not differentiated

Gastrula – diploblastic– Blastopore – Opening to outside– Archenteron- new “gut”

Cnidarians– Diploblastic & radially symmetrical

Embryonic tissue layers

Ectoderm Endoderm

Triploblastic animals also have: Mesoderm forms in between other two

layers.

Origins of animals???

Figure 32.1 Early embryonic development (Layer 3)

Two Views of Animal Diversity

The traditional view based on body plan and embryonic development.

The new view is based primarily on molecular characteristics.

The Traditional View

Parazoa vs Eumetazoa Parazoa lack true tissues (special cell connections) Eumetazoa are all the other animals

Traditional Phylogeny

The Traditional View

Radiata vs Bilateria

Traditional View Continues

Acoelomate - Pseudocoelomate vs Coelomate

Traditional View Continues

Protostome vs Deuterostome

Fig. 21.37a

Protostomates

Spiral and determinate cleavage-– Cell fate (specialization) starts during cleavage

Mesoderm forms from a ball then splits open to form a cavity (ceolom)

New opening forms an anus, blastopore becomes mouth.

Proto (first) stomate (mouth)

Deuterostomates

Radial and indeterminate cleavage-– Cell fate (differentiation) starts after cleavage– Identical twins

Mesoderm forms from pockets in endoderm. Always has a gap or cavity in side

New opening forms a mouth, blastopore becomes anus.

Deutero (second) stomate (mouth)

Protostome vs Deuterostome

I am a protostome. This opening will form my

mouth

I am a deuterostome

. This opening will

form my anus.

TraditionalPhylogeny

Traditional Characters

Phylogeny based on SSU-rRNA

The New View

Parazoa vs Eumetazoa - same Radial vs. Bilateral - same Protostomate vs. Deuterostomate – still significant Aceolomate and Pseudoceolomate traits not as

significant. Considered simplified versions of ceolomates.

Groups Nematodes with Arthropods in one branch and the rest of the protostomates in another branch.

Phylogeny Comparison

Molecular groupings

Metazoan phylogenies

Adoutte A. et.al. PNAS 2000;97:4453-4456

©2000 by The National Academy of Sciences

Lophotrochozoa

Protostomate Have Trochophore larvae –

– Bands of cilia

Also include the Lophophore phyla –– Ciliated feeding structure

Joins the Annelids – Mollusks onto the same clade

Larvae

Juvenile ( pre – reproductive) phase Have simpler morphology than adult Often move, and feed differently than adults

– Swims vs. crawls or flies

Often live in different habitats to avoid competing with adults

Often are the dispersal stage

Trochophore Larvae

AnnelidaMollusca

Lophophorate

ectoprocts

Ecdysozoa

Based on molecular data Joins Nematodes and Arthropods Both groups have hardened exoskeletons

and undergo Ecdysis (Molting)

Molecular clades

Includes some aceolomates and pseudocelomates into the different clades

Not pre-ceolomates, but were rather simplified later.

THE END?

WOW!!!!!!!!!!!!

This is going to take a lot of study.