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Animal Architecture

Whither Deuterostomes?A. Some researchers consider the

deuterostomes an ancestral group relative to the rest of the animal taxa.

a. Note that it IS possible to rotate the phylogeny around the Deuterostome-Protostome node.

Rotation at the Proto-Deutero Node

The BauplanConcept

What It Means1. Refers to the structural and

functional "plan" of an organisma. Doesn't mean that an architect

designed it, although there often is that appearance

b. A simpler explanation lies in natural selection acting on population variation.

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This Results In:1. Body coloration due to how well an

organism matches its surroundings.2. Body shape determined by how well

certain appendages permit locomotion, food capture, defense.

3. Body machinery determined by how well materials are processed, transported, excreted.

Observed Phenotypes1. Are the accumulation of successful

characteristics, passed on to offspring.

a. Characters persist because they allow their possessors to survive and reproduce.

b. Also, due to influences of random factors such as chance, physical constraints, and evolutionary history.

What It MeansAll components of the "bauplan" must

work effectively as a whole.a. And because natural selection works

primarily on the organisms,1. The necessary functional

interrelationship of the systems and structures interacts with the historical component inherent in living systems.

What It Means. 2. This produces certain patterns of

organization that persist over evolutionary time.

3. Manifested as major phyla, classes, orders of organisms.

What are the components of a "Baupläne?"

Cellularitya. Whether or not the organism has

cells.b. It may or may not be advantageous to

have them.

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Body Symmetrya. How is the body arranged around one

or more axes?b. Certain shapes benefit feeding,

locomotion.

Organ Systems The mechanisms required to run

multicellular organisms.

1. Support and movement a. System of supporting, protective,

mechanical elements that permit the body to support itself and/or move.

Organ Systems 2. Energy acquisitiona. Means for capturing, processing and

utilizing energy sources from the external enviroment.

Organ Systems 3. Osmoregulation and excretiona. means for regulating flow of water

and wastes into and out of the body.

Organ Systems 4. Materials transporta. Means for moving materials within

the body.b. Essential for multicellular organisms

Organ Systems 4. Gas exchange1. Obtain oxygen, remove CO2, other

gaseous wastes.

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Organ Systems 5. Information processinga. Nervous system for receiving,

processing, responding to internal and external stimuli.

b. Hormonal control of internal processes.

Organ Systems 6. Reproductiona. Repair of genetic, somatic structures.b. Production of new individuals; as

clones or as gametes.

Why be Multicellular?1. There are lots of advantages to unicellularity.

2. Evidenced by the success of the Protozoa:

a. rapid reproductionb. exploitation of microhabitatsc. opportunities for dispersal, resistant

forms widespread.

Why be Multicellular?3. But, there are also advantages to

being larger:a. Large size, multicellularity permits: 1. predator escape2. greater variety of foods3. greater specialization4. greater capacity to tolerate unstable

environment.

In Short, 1. Once situations existed that

permitted multicellularity,a. Perhaps existence of oxygen

(produced by plants)2. Multicellularity led to explosive

adaptive radiation (preCambrianExplosion, >600 myr ago).

a. Result: Multicellular animals: METAZOA.

What happens when you

become larger and more complex?

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Cellularity, Revisited

Certain Organisms Don't Exist

1. There are no 800 lb amoebas.a. There are no single-celled squid, sea

stars.b. Why?c. Because there are physical

constraints on life.

Physical Constraints on Life1. Most living systems involve ionic

chemistry; what molecules can do in water

2. There are physical limits on size.3. Phylogenetic limits exist -a. genetic variation.b. evolutionary history.c. selection intensity.

Physical Constraints on Life1. Substances must enter and exit cells

through the cell membranea. Thus, the physical relationship

between surface area and volume places a limit on cell size.

Consider a Cube1. With 1 cm sides:

a. Each side: 1x1 = 1cm2

b. Total surface area: 6(1) = 6 cm2

c. Volume: base area x height = 1x1

= 1 cm3

d. s.a./vol. ratio: 6/1 = 6

Consider Another Cube

2. With 2 cm sides:1. each side: 2x2 =

4cm2

2. total surface area: 6(4) = 24 cm2

3. volume: base area x height = 4x2 = 8 c3

4. s.a./vol. ratio: 24/8 = 3

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What Does It Mean?

If You Get Larger:1. Increasing volume->increasing

cellular activity ->increased nutritional requirements, increased waste production.

2. Thus, by dividing organism into smaller parts, increased efficiency at materials transport.

a. Sponges absorb better than paper towels.

If You Get More Complex:1. Increased cell numbers, increased

size = increased complexity.a. Individual cells are limited in their

ability to do different things.b. But: increased cell numbers permits

cellular specialization.c. Increased efficiency is obtained by

increased specialization.

Venus Williams vs. the Arizona Cardinals

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If You Get More Complex:2. Greater specialization, however,

necessitates maintenance mechanisms.

a. nerve cells aren't very good at catching their own food.

b. Required systems: the ones mentioned above.

Tissue Organization

Cellular Associations1. Multicellular animals may consist of

loosely organized groups of cellsa. little specializationb. little integration among functional

groups of cells2. Examples:a. Spongesb. Mesozoa - linearly arranged clusters

of cells.

Porifera

MesozoaTrue Tissues

1. Cells arranged as functional units.a. Specialization of structure and

function.b. Usually arranged in systems and

organs.2. Arrangement is often laid down early

in development.

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Diploblastic Arrangement1. Epidermis - outer layer2. Gasterodermis - inner, digestive layer3. Mesenchyme - middle layer of cells,

but no true mesodermb. Examples:1. cnidarians, ctenophores

Aurelia aurita

Pleurobrachia sp. Triploblastic Arrangement1. Epidermis - outer layer, derived

from embryonic ectoderm.2. Endodermis - digestive layer,

derived from endoderm3. Mesodermis - inner muscle, organ

layers, derived from mesoderm

Notoplana acticola

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Body Symmetry

How ARE Organisms Arranged?

Spherical1. Cody of the organism is arranged so

that any plane can cut it into equal parts

2. Relatively few examples in metazoaexcept early in development

3. Protozoaa. radialariab. multicellular algae: Volvox

Pandorina sp.

Astrolithium sp.Irregular

1. Body of organism is arranged so that no plane cuts it into equal parts.

2. Examples:a. amoebaeb. sponges3. Neither spherically nor irregularly

symmetrical organisms have polarity

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Mayorella sp. Isodictya sp.

Mycale loveniRadial

1. Body is arranged along a longitudinal axis (varying in length).

a. Often with oral, aboral endsb. Polarity is established2. Planes drawn parallel to the

longitudinal axis divide the animal into equal halves.

3. Often associated with sessile feeding.

Haliplanella luciae Pachycerianthus fimbriatus

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Biradial1. Similar to radial symmetry except

that only two planes will cut the animal into equal halves.

a. Usually some secondary specialization on feeding arrangement

2. There can be more involved versions of this.

a. triradial, pentaradial, etc.

Metridium senile

Fungia scutariaBilateral

1. A single plane divides the body into equal halves.

2. often with other functional surfaces.a. dorsal, ventral, lateral.b. anterior, posterior.3. Usually locomotory specialization4. Often associated with cephalization

(association of nervous tissue in anterior end).

Chaetonotus sp. Urechis caupo

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Apis mellifera

Body Cavity Arrangement

Acoelomates1. Possess no body cavity2. Instead, parenchyma tissue and

muscles.3. Examples:a. Platyhelminthesb. Nemerteans

Bipalium kewense

Opisthorchis sinensis An Antarctic nemertean

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Pseudocoelomates1. Possess a body cavity, 2. Fluid filled pseudocoel; organs

supported by hydrostatic pressure.3. Lack mesenteries4. Examples:a. Blastocoelomate (Ascelminth) phyla

Corynosoma sp.

A horsehair worm Pycnophyes greenlandicus

Eucoelomates1. Possess a body cavity2. Not fluid filled or under pressure3. Organs supported by mesenteries4. Examples:a. all other phyla

Opisthopus transversus

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Florometra serratissima