ANIMALS

TOPIC 10: INTRODUCTION TO ANIMALS

DOMAIN EUKARYA

  • Bikonta

  • Unikonta

  • Stramenopila

  • Alveolata

  • Rhizaria

  • Plantae

  • Excavata

  • Opisthokonta

ANIMALS

  • Opisthokonta

  • Choanoflagellates

  • Fungi

  • Amoebozoa

ANIMAL CHARACTERISTICS

  1. Multicellular

  2. Extracellular matrix made of collagen

    • Collagen: An elastic connective tissue located in skin, muscles, cartilage, and bones; it is one of the most common proteins in the animal body.

  3. Heterotrophic: Animals cannot produce their own food and must consume other organisms.

  4. Movement:

    • Enables finding food or mates

    • Allows for escaping from predators

    • Facilitates dispersal to new habitats

    • All animals (except sponges) possess muscle and nervous tissue to achieve movement.

  5. Most are diploid with haploid gametes:

    • Diploid (2n) represents two copies of each chromosome, while haploid (n) represents one copy.

    • Zygote (2n) develops into a larva (2n), which then undergoes transformation into juvenile (2n) and adult (2n) forms.

  6. Development via a Blastula:

    • A blastula is a hollow ball of cells formed during early embryonic development. The formation of the blastula allows for tissue differentiation.

METAMORPHOSIS

  • Definition: A massive morphological change occurs between juvenile and adult life cycle stages.

    • This process allows for minimized competition for resources between juvenile and adult forms.

    • It enables movement for species that are sessile in the adult stage.

ANIMAL CATEGORIZATION

  1. Body Symmetry:

    • (a) Asymmetry: No planes of symmetry, e.g., sponges.

    • (b) Radial symmetry: Multiple planes of symmetry, e.g., sea anemones.

    • (c) Bilateral symmetry: Single plane of symmetry, e.g., lizards.

    • (d) Pentaradial symmetry: Five planes of symmetry, common in echinoderms.

  2. Tissue Layers:

    • Ectoderm: External layers, such as the epidermis.

    • Endoderm: Internal tissue lining, such as the gut.

    • Mesoderm: Musculature and lining of the body cavity.

    • Organizational structures:

      • No tissue layers: Present only in Porifera (sponges).

      • Diploblastic: Two layers (endo and ectoderm).

      • Triploblastic: All three germ layers present.

  3. Gut Type (Digestive Tract Organization):

    • Two-way/Incompletely Blind Gut: One opening where the animal both ingests and excretes.

    • One-way/Complete Gut: Two openings, with ingestion occurring at the mouth and excretion at the anus.

    • Processing Gut: One-way with specialized regions for the completion of distinct digestive tasks (e.g., human digestive system).

  4. Body Cavity Type:

    • Coelom: Hollow body cavity fully lined with mesoderm, which allows for independent movement of internal organs.

    • Acoelomate: Triploblastic organisms that lack a coelom.

    • Coelomate: Triploblastic organisms with a fully lined coelom.

    • Pseudocoelomate: Triploblastic organisms with an incompletely lined coelom.

  5. Nervous System Organization & Cephalization:

    • Early Nervous System: Diffuse nerve net predominantly observed in some primitive organisms like hydra.

    • Late Nervous System: Development of a central nervous system (CNS) featuring a brain with connected nerve systems.

    • Cephalization: Concentration of nerve and sensory tissue at one end of the body, common in bilaterally symmetrical organisms, facilitating directional movement.

CAUSES OF ANIMAL DIVERSIFICATION

  1. High oxygen levels during the Cambrian Explosion facilitated more efficient aerobic respiration leading to larger, more active animals.

    • The energy change relative to glucose when oxygen is used as the final electron acceptor can be almost 700 ext{ kcal/mol}.

  2. Increase in food availability led to diverse feeding strategies and niches.

  3. Predatory feeding strategies spurred the evolution of protective structures and sensory organs in prey.

  4. New niches arose as animals explored environments beyond the ocean floor, leading to greater biodiversity and complex interactions.

  5. Developmental regulatory genes, which activate protein-coding genes, played a pivotal role in body organization.

    • Example of Hox Genes: Hox genes dictate the archetype of body organization and are highly conserved across species.

TAKE HOME MESSAGES ON ANIMAL DIVERSIFICATION

  1. Animal evolution does not strictly follow a linear path of complexity; it is multifaceted.

  2. Key innovations and adaptations have occurred over large timescales rather than instantaneously.

  3. Evolution continues to occur within every lineage of animals, showcasing the ongoing nature of evolutionary processes.