Zoology and Evolution

Zoology

• The scientific study of animals

• What is an animal?

Evolutionary Tree of Life

Animals

• Multicellular eukaryotes

• Heterotrophs (consumers)

• Develop through a blastula stage

• Motile at some stage of their life

Choanoflagellate Protozoan

• Simple colonial flagellates

• No specialization

• Precursor to Metazoa

Spherical Colonies of Choanoflagellates

• Reproduction of the whole cell aggregate through gametes

• Cell specialization

Animal Kingdom Includes Very Diverse Organisms

Cell level of specialization

• Porifera

Tissue level of specialization

• True tissues– Endoderm– Ectoderm

• Example– Cnidaria

Organ level of specialization

• Tissues form organs

• Three germ layers– Ectoderm– Mesoderm– Endoderm

• Example– Platyhelminthes

Complete alimentary canal

• Mouth and anus

• Example– Nematoda

Internal body cavity - Coelom

• Organs suspended inside body cavity

• Example– Annelida

Invertebrates – Animals without a backbone

Vertebrates – animals with a backbone

Evolution

• Process of organic development and change– Continual process– Driven by the environment– Organisms have built in potential for change

Perpetual Change

Common Descent

• Phylogeny– Common descent through branching lineages

• Evidence– Homologies – similarity between organism that

occur because of common ancestry• Structural

• Genetic

Skeletal Homologies

Similarities because of common descent

Skeletal Homologies

Similarities because of common function

Evolutionary Relationships Revealed During Embryonic Development

Multiplication of Species

• Reproductively distinct populations of organisms– Usually but not always differ in form– No interbreeding between species in the wild

• Species split and develop into new species

Gradualism and Punctuated Equilibrium• Gradualism

– Small changes accumulate over time

– Steady rate of change

• Punctuated equilibrium– Bursts of rapid change

followed by little change

– Rate of change varies

Natural Selection

Responses to Selection

Sexual Selection

• Results in some sexual dimorphism

Potential for Variation

Modern View

• Microevolution– Small-scale changes– Change within a species

• Macroevolution– Large-scale changes– Formation of new species