Bio 100 - Study Guide 18

The Evolution of Animal Diversity

Overview: Welcome to Your KingdomLearning Objectives

• Characteristics of Animals

• Origin of the Animal Kingdom

• Symmetry

• Segmentation

• Characteristics of Chordates….Vertebrates

• Phylogeny of the Animal Kingdom

Characteristics of Animals-Learning Nutritional Mode

• Animals are heterotrophs that ingest their food

https://www.msu.edu/course/isb/202/ebertmay/notes/inotes/01_25_07_carbon.html

Cell Structure and Specialization

• Animals are multicellular eukaryotes• Their cells lack cell walls• Their bodies are held together by

structural proteins such as collagen• Nervous tissue and muscle tissue are

unique to animals

Reproduction and Development

• Most animals reproduce sexually, with the diploid stage usually dominating the life cycle

• After a sperm fertilizes an egg, the zygote undergoes cleavage, leading to formation of a blastula

• The blastula undergoes gastrulation, forming embryonic tissue layers and a gastrula

LE 32-2_3

Zygote Eight-cell stage

Cleavage

Blastula Cross section

of blastula

Cleavage

Blastocoel

Blastocoel

Endoderm

Ectoderm

GastrulaBlastopore

Gastrulation

• Many animals have at least one larval stage

• A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis

• All animals, and only animals, have Hox genes that regulate the development of body form

• Although the Hox family of genes has been highly conserved, it can produce a wide diversity of animal morphology

The history of animals may span more than a billion years

• The animal kingdom includes not only great diversity of living species but also the even greater diversity of extinct ones

• The common ancestor of living animals may have lived 1.2 billion–800 million years ago

• This ancestor may have resembled modern choanoflagellates, protists that are the closest living relatives of animals

LE 32-3

Stalk

Single cell

Two distinct features that had to have preceded true

multicellularity.

1. The obvious feature is that cells must stick together;

specific adhesion molecules must be present that link cells

together, that aren't generically sticky and bind the organism

to everything. So we need molecules that link cell to cell.

2. A feature that distinguishes true multicellular animals from

colonial organisms is division of labor — cells within the

organism specialize and follow different functional roles. This

requires cell signaling, in which information beyond simple

stickiness is communicated to cells, and signal transduction

mechanisms which translate the signals into different patterns

of gene activity.

http://7salemanimalkingdom.wikispaces.com/Sponges

Tube Sponge

LE 32-4

Hollow sphereof unspecializedcells (shown incross section)

Somatic cells

Colonial protist,and aggregate ofidentical cells

Gastrula-like“protoanimal”

Beginning of cellspecialization

Reproductive cells

Infolding

Digestivecavity

Paleozoic Era (542–251 Million Years Ago)

• The Cambrian explosion marks the earliest fossil appearance of many major groups of living animals

• There are several hypotheses regarding the cause of the Cambrian explosion

http://www.astrobio.net/exclusive/2419/our-earliest-animal-ancestors

The Cambrian explosion or Cambrian radiation was

the relatively rapid appearance, over a period of many

million years, of most major Phyla around 530 million

years ago, as found in the fossil record. This was

accompanied by a major diversification of other

organisms, including animals, phytoplankton, and

calcimicrobes. Before about 580 million years ago,

most organisms were simple, composed of individual

cells occasionally organized into colonies. Over the

following 70 or 80 million years the rate of evolution

accelerated by an order of magnitude (as defined in

terms of the extinction and origination rate of species)

and the diversity of life began to resemble today’s.

Charles Darwin considered this sudden

appearance of many animal groups with few or

no antecedents to be the greatest single

objection to his theory of evolution. He had even

devoted a substantial chapter of The Origin of

Species to solving this problem.

Symmetry

• Animals can be categorized according to the symmetry of their bodies, or lack of it

LE 32-7a

Radial symmetry

Bilateral symmetry

Bilaterally symmetrical animals have:

A dorsal (top) side and a ventral (bottom) side

A right and left side

Anterior (head) and posterior (tail) ends

Cephalization, the development of a head

Tissues• Animal body plans also vary according to the

organization of the animal’s tissues

• Tissues are collections of specialized cells isolated from other tissues by membranous layers

• Animal embryos have concentric layers called germ layers that form tissues and organs

• Ectoderm is the germ layer covering the embryo’s surface

• Endoderm is the innermost germ layer

• Diploblastic animals have ectoderm and endoderm

• Triploblastic animals also have an intervening mesoderm layer

Body Cavities

• In triploblastic animals, a body cavity may be present or absent

• A true body cavity is called a coelom and is derived from mesoderm

A coelomate animal (mollusks, annelids, and all of

the more complex animals) is basically a set of

concentric tubes, with a gap between the gut and

the outer tubes.

(mollusks, annelids, and all of the more complex animals)

LE 32-8a

Coelom

Coelomate

Body covering

(from ectoderm)

Digestive tract

(from endoderm)

Tissue layer

lining coelom

and suspending

internal organs

(from mesoderm)

LE 32-8b

Body covering

(from ectoderm)

Digestive tract

(from endoderm)

Muscle layer

(from

mesoderm)

Pseudocoelom

Pseudocoelomate

A pseudocoelom is a body cavity derived from the

blastocoel, rather than from mesoderm

LE 32-8c

Body covering

(from ectoderm)

Wall of digestive cavity

(from endoderm)

Acoelomate

Tissue-

filled region

(from

mesoderm)

Acoelomates are organisms without body

cavities

Leading hypotheses agree on major features of the animal phylogenetic

tree

• Zoologists recognize about 35 animal phyla

• Current debate in animal systematics has led to the development of two phylogenetic hypotheses, but others exist as well

• One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons

The two major types of coelomates are protostomes and

deuterostomes. These groups differ in the characteristics of early

development.

LE 32-10

Deuterostomia“Radiata”

Bilateria

Protostomia

Metazoa

Eumetazoa

Ancestral colonialflagellate

• One hypothesis of animal phylogeny is based mainly on molecular data

LE 32-11

Deuterostomia

“Radiata”

Bilateria

Lophotrochozoa

Metazoa

Eumetazoa

Ancestral colonialflagellate

Ecdysozoa

Points of Agreement

• All animals share a common ancestor

• Sponges are basal animals

• Eumetazoa is a clade of animals with true tissues

• Most animal phyla belong to the clade Bilateria

• Vertebrates and some other phyla belong to the clade Deuterostomia

Disagreement over the Bilaterians

• The morphology-based tree divides bilaterians into two clades: deuterostomes and protostomes

• In contrast, recent molecular studies assign two sister taxa to protostomes: the ecdysozoans and the lophotrochozoans

http://www.brsd.org/education/components/scrapbook/default.php?sectiondetailid=4125&&PHPSES

SID=8907e11c0c2c592b81323e6a645eeff7

http://www.utexas.edu/features/2008/tree/

The End