Chapter 32 – Animal Diversity

Key Concepts Animals are multicellular, heterotrophic eukaryotes with tissue that develop from embryonic layers. Animal history spans more than ½ billion years. Animals can be characterized by Body Plans. Changes in animal phylogeny are emerging from molecular data.

Animals differ from plants and fungi in their Nutritional Modes Animals differ from plants and fungi in their mode of nutrition. Plants are autotrophs: generate organic molecules through photosynthesis. Fungi are heterotrophs: absorb organic molecules by growing on or near food. (digestive enzymes – produced outside body) Animals are heterotrophs: ingest organic molecules; living and non-living. (digestive enzymes – produced inside body)

Cell Structure Animals are multicellular eukaryotes. They lack structural support from cell walls, but are held together with structural proteins and collagen. Collagen is specific to animals; its not found in plants or fungi. (most abundant protein in animal K.) Animals also have muscle and nerve cells, not seen in other multicellular organisms. These qualities are central to what it means to be an animal. Collagen is the most abundant protein in the animal kingdom. Mainly found in connective tissue and bone. It is the muscle and nerve cells that allow for many of the adaptations that differentiate animals from plants and fungi. In other words these structures are central to what it means to be an animal.

Animal Embryonic Development Cleavage: succession of mitotic cell divisions without cell growth – forms a blastula (hollow ball is multi-cellular). Cleavage Cleavage Blastula Zygote Eight-cell stage Cross section of blastula

Zygote Gastrulation Cleavage Eight-cell stage Cleavage Blastocoel Cross section of blastula Blastula Figure 32.2-3 Early embryonic development in animals (step 3) Gastrulation The next phase of formation is the gastrula. Where layers of embryonic tissue will eventually turn into body parts. Cross section of gastrula Blastocoel Endoderm Ectoderm Blastopore Archenteron

Zygote – Cleavage – Blastula – Gastrula Blastocoel Archenteron Endoderm Cleavage Cleavage Blastula Ectoderm Zygote Eight-cell stage Gastrulation Gastrula Cross section Blastopore Takes place before cells develop into the different body Parts. Cross section of blastula

Animal Growth & Progression In addition to mitotic cell division; many organisms also (ie. macro inverts.) have a Larval Stage. Sexually immature stage; morphologically distinct from the adult. Animals in their larval stage tend to eat different food, and have different behaviors than a sexually mature adult. Undergo metamorphosis; juvenile animal that resembles the sexually mature adult.

Animal History The animal kingdom includes a great diversity of living species. As well as an even larger diversity of extinct species. Possibly 99% of all animals sp. Some studies suggest animals diverged from ancestors of fungi a billion years ago. Others suggest a common protist; lived between 675-875 million years ago. Earth is approximately 4.5 billion years old.

Researchers have also hypothesized that the common ancestor of living animals may have been a stationary feeder similar to present day choanoflagellates. Individual choanoflagellate Choanoflagellates OTHER EUKARYOTES Sponges KO-an-O-cyte. Animals Collar cell (choanocyte) Other animals

Animal Evolution There is fossil evidence that animals have evolved from distant ancestors over four geologic eras: Neoproterozoic (1 Billion - 542 m.y.a.) Paleozoic (542 - 251 m.y.a.) Mesozoic (251- 65.5 m.y.a.) Cenozoic (65.5 m.y.a.)

Neoproterozoic Era The first macroscopic fossils of animals are dated to approximately 550 million years old. Multicellular eukaryotes known from Australia; Ediacaran biota ~ soft body mulluscs, snails, and possible relatives of sponges and anemones. In general the fossil record suggests : the end of the Neoproterozoic era was a time of increasing animal diversity. Older fossils may still be found, but at this point china and australia have the oldest recorded fossils.

(a) Mawsonites spriggi (b) Spriggina floundersi Fig. 4 1.5 cm 0.4 cm Fossils with radial symmetry and segmented bodies. (a) Mawsonites spriggi (b) Spriggina floundersi

Paleozoic Era (542-251 million) Dramatic acceleration of animal diversity during the Cambrian era which was 535-525 m.y.a. Cambrian explosion! Precambrian strata has only a few animal phyla in comparison. Approximately half of all extinct animal phyla are found in these rock layers. first arthopods, then cordates, and echinoderms Several hypotheses are have emerged as to why…

Fig. 5 Cambian landscape

Cambrian Explosion Theories New predator-prey relationships were created through natural selection. - Predators acquired better locomotion - Prey acquired protective shells. Oxygen Levels increased dramatically preceding the Cambrian explosion. - Animals with higher metabolic rates and larger body sizes thrive.

3) Hox gene complex allowed for developmental flexibility that resulted in morphologic variations. These hypotheses are not exclusive – they all may have played a role in animal diversity.

Diversified into numerous terrestrial groups. Toward the end of the Paleozoic era animal diversity continued to increase, but was followed by periodic episodes of extinction. It was during this time vertebrates made the transition to land. (365 m.y.a) Diversified into numerous terrestrial groups. Amphibians; frogs and salamanders Amniotes; reptiles and mammals

Mesozoic Era Animals spread into new ecological habitats. - first coral reefs formed - some reptiles returned back to the water - winged animals evolved - small dinosaurs emerged More mammals, flowering plants and insects also emerged.

Cenozoic Era Mass extinctions of terrestrial and marine animals. (65.5 m.y.a) We lost large non-flying dinosaurs and many marine reptiles. Large mammalian herbivores and predators exploited the vacated ecological niches. Global climate was cooling. Changed behaviors (ie; primates moved to open woodlands, and savanas)

Body Plans A set of morphological and developmental traits. Important to remember- similar body plans can evolve independently. (convergent evolution) Physical constraints tend to dictate form. Body plans => characterized by symmetry.

(b) Bilateral symmetry Fig. 7 (a) Radial symmetry Many animals have sensory equipment, and/or brains at their anterior end. An evolutionary trait called cephalization. So which symmetry do you think leads to a more active lifestyle? (b) Bilateral symmetry

Body Plans Radial symmetry: have a top and a bottom, no front and back. Bilateral symmetry: has a left and right, top and bottom, and cephalization (conc. sensory equip.) Dorsal = Top Ventral = Bottom Anterior = Front Posterior = Back

Tissue Ectoderm – germ layer covers the outer surface of the organism. (also central nervous system) Endoderm – germ layer lines most inner surfaces. Creating digestive tract and organs. Animals with radial symmetry tend to be diploblastic – two layers. (Cnidarians) Animals with bilateral symmetry are triploblastic – and have a 3rd layer. Mesoderm – germ layer that forms the connective tissue and muscles surrounding the organs. What would humans be?

Triploblastic Organisms Coelomates: have body cavity made of mesoderm; suspends internal organs. Digestive tract is formed by endoderm. Pseudocoelomates: have body cavity, no organs. Just a digestive tract made of mesoderm and endoderm. Acoelomates: lack a body cavity or coelom.

Coelom Body covering (from ectoderm) Tissue layer lining coelom Fig. 8a Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) Seal – em-ates (a) Coelomate

Body covering (from ectoderm) Pseudocoelom Muscle layer (from Fig. 8b Body covering (from ectoderm) Pseudocoelom Muscle layer (from mesoderm) Digestive tract (from endoderm) (b) Pseudocoelomate

Wall of digestive cavity (from endoderm) Fig. 8c Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm) (c) Acoelomate

Divergent Development Protostome versus Deuterostome Development modes are distinguished by differences in cleavage, coelom forms, and fate of the blastopore.

Planes of cell division are diagonal to the vertical access. Fig. 9a Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (a) Cleavage Eight-cell stage Eight-cell stage Spiral and determinate Radial and indeterminate Planes of cell division are diagonal to the vertical access. Planes of cell division are parallel or perpendicular to vertical access.

Protostome development (examples: molluscs, annelids) Fig. 9b Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (b) Coelom formation Coelom Key Ectoderm Archenteron Mesoderm Endoderm Coelom Mesoderm Blastopore Blastopore Mesoderm Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom (outpocketing).

Proto = first Deuteros = second Stroma = mouth Stroma = mouth Fig. 9c Proto = first Stroma = mouth Deuteros = second Stroma = mouth Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (c) Fate of the blastopore Anus Mouth Key Ectoderm Digestive tube Mesoderm Endoderm Mouth Anus Mouth develops from blastopore. Anus develops from blastopore.

Phylogenic Tree Historic accounts of evolution have typically been based on morphologic structure. Molecular evidence is now changing the way Clades have been traditionally organized. DNA and RNA analysis – changing how we see ancestor relations.

Old World View - Based on Morphology Fig. 10 “Porifera” Cnidaria ANCESTRAL COLONIAL FLAGELLATE Metazoa Ctenophora Eumetazoa Ectoprocta Brachiopoda Deuterostomia Echinodermata Chordata Bilateria Platyhelminthes Old World View - Based on Morphology Rotifera Protostomia Mollusca Annelida Arthropoda Nematoda

Currently Accepted Phylogenic Tree