The Evolution of Animal Diversity

1. The Evolution of Animal Diversity

2. What Characteristic Define an Animal? • Eukaryotic cells • Multicellular • Ingestive Heterotroph

3. Other Common Characteristics of Animals • Lack cell walls • Sexual reproduction • Diploid, except for gametes • Excitable (nervous & muscular) tissue • Similar embryology (blastula & gastrula)

4. Early embryonic development

6. Early embryonic development blastula gastrulation gastrula

7. Animal Diversity

8. How did the animal kingdom evolve? - Oldest fossils are 700 million years old • Animals probably evolved from an ancestor of a colonial choanoflagellate • protist

9. One hypothesis for the origin of animals

10. Major Trends in Animal Evolution: • Development of Tissue Layers • Patterns of Body Symmetry • Development of a Body Cavity • Body Segmentation

11. Major Trends in Animal Evolution: Development of Tissue Layers Most animals have tissues that arise from three embryologic tissues layers: • Ectoderm – produce skin and nervous system • Endoderm – produces GI tract • Mesoderm – produces muscle, skeleton and most organs

12. Three embryologic tissue layers Ectoderm Endoderm Mesoderm

13. Major Trends in Animal Evolution: Patterns of Body Symmetry • Asymmetrical • Bilateral symmetry • Radial symmetry

14. Body symmetry Radial = any cut through main body axis produces mirror image halves Bilateral = a cut through main body axis produces right-left halves

15. Major Trends in Animal Evolution: Development of a Body Cavity: • Allows independent movement of body wall • Cushions internal organs • Provides a hydrostatic skeleton • Increases flexibility and mobility

16. Major Trends in Animal Evolution: Development of a Body Cavity: • Coelomate – true body cavity fully lined with mesoderm • Pseudocoelomate – body cavity in direct contact with gut • Acoelomate – lack body cavity

17. Acoelomate Pseudocoelomate Coelomate

18. Coelomates: Protostomes VS Deuterostomes Protostomes: mesoderm forms from mass of cells between endoderm and ectoderm Deuterostomes: mesoderm forms as outpocketing of gastrulation cavity

19. Protostomes Deuterostomes Visualizing Protostome & Deuterostome Development

20. Major Trends in Animal Evolution: Body Segmentation • Most animals have segmented bodies • Segmentation increases body flexibility and mobility

21. Forms of asexual reproduction • fission: splitting off of new individual from existing one, parent cell divides into two parts • budding: new individual grows from body of original, can detach (solitary lifestyle) or remain attached (colonial lifestyle) • fragmentation: breaking of the body into several pieces, each of which forms a complete adult (aka regeneration) • gemmulation: release of specialized groups of cells that are enclosed in a capsule and grow into new individuals

22. Sexual Reproduction • Two haploid gametes (produced by meiosis)fuse to form a diploid zygote. • female gamete = ovum = unfertilized egg; usually large and non-motile cell. • male gamete = spermatozoan = small, usually flagellated cell. • Fertilization occurs in two ways: • external fertilization -eggs & spermatozoa are shed into the environment. • internal fertilization -sperm are deposited or near the female’s reproductive tract and egg and sperm unite within the female’s body.

28. Phylogenetic tree of Kingdom Animalia

29. Phylum Porifera: Sponges Probably first animals to evolve – similar to modern colonial choanoflagellate protist

30. Early embryonic development

31. What was the distinguishing characteristic that differentiated a true multicellular organism and a colonial protist?

32. Sponges have specialized cellsthat exhibit cellular recognition but lack true tissue layers Osculum Epithelial cells Porocyte cell Choanocytes – specialized for obtaining food Noncellular mesoglea and skeletal components Ameobocytes- specialized for digestion, nutrient transport, waste disposal, skeletal component manufacure. Can change into other cell types. Anatomy of a Sponge

33. Sponges can reproduce sexually or asexually Sponges are hermaphrodites, producing both sperm and eggs.

34. Sexual Reproduction Motile sponge larva Newly settled sponge

35. Asexual Sponge Reproduction 1. Budding 2. Gemmules Sponge Reproduction

36. Sponge Classes • Demospongae (spongin) • Calcarea (Ca) • Hexactinella (Si)

37. Major Trends in Animal Evolution: 1. Evolution of tissue layers

38. Phylum Cnidaria Coelenterata): Jellies Hydra Anemones Corals

39. Phylum Cnidaria Characteristics: • Radial symmetry • True tissue layers (but only 2, not 3) • Cnidocytes/nematocysts (stinging cells) for prey capture • Gastrula stage of development • Digestive (gastrovascular) cavity • Diversity of Living Things: Phylum Cnidaria • Phylum Cnidaria (Jellyfish, Sea Anemones, Corals, Sea Combs) • Phylum Cnidaria: The Stinging Animals

40. Nerve Net, with nerve cells, but not centralization/brain • Excretion of water through specialzed cells • Both extracellular and intracellular digestion • One opening -2 way digestive system • Dioecious • Planula/ciliated larvae

41. Radial symmetry Radial symmetry allows a sessile animal to meet its environment equally from all sides Arms & Camp, 1995

42. Early embryonic development blastula gastrulation gastrula

43. Polyp and medusa forms of cnidarians Medusa Polyp Purves et al., 1992

44. Cnidocytes and nematocysts Firing Nematocysts Brum et al., 1994

48. For jellies and hydra: For anemones and corals: A comparison of poriferans & cnidarians

49. Coral reefs have enormous biodiversity.