Animals What are they? Where did they come from? What are their evolutionary novelties? What characterizes their diversification?

What synapomorphies unite Animals (Metazoans)? • Multicellular • Heterotrophs • Obtain organic & inorganic compounds by ingestion • Move under their own power at some point in their life cycle

Phylogeny of Eukarya & Protists • Based on a few important morphological synapomorphies & growing DNA synapomorphies

Who are the closest relatives of Animals?

• DNA synapomorphies unite Animals & Fungi • Both synthesize chitin • Single, posterior Flagella of fungi & Animal gametes are homologous • Use same energy storage molecule: glycogen • What do plants use to store energy?

Clicker Q •

1. 2. 3.

Which node marks the MRCA of Land Plants & Green Algae?

Probable evolution of Animals • From single celled or colonial Choanoflagellate ancestor – Formation of colonies – Specialization of cells – Interdependence of cells

Synapomorphies DNA sequence; Animal specific proteins (collagen; adherins) found in choanoflagellates

Morphologically identical to Sponge collar cells

Collar cells also found in basal Animals; never in Protists, Plants or Fungi

Typical Animal Life Cycle • Most are 2n & reproduce sexually • Diploid (2n) stage is dominant • Tissue differentiation – Ectoderm – Endoderm

• Structures that produce gametes are contained within sporophyte

What are Animals (Metazoans)? • Multicellular • Heterotrophs • Obtain organic & inorganic compounds by ingestion • Move under their own power at some point in their life cycle

Main avenues of diversification • Changes of body plan – Number & type of tissue layers (specialized cells) – Plane of symmetry – Presence & type of body cavity – Early developmental changes – Increased cephalization & organ system complexity

Clicker Q •

How are Animal life cycles similar to Seed Plant life cycles?

1. 2. 3. 4. 5.

The 2n stage is dominant Gametes are asymmetric in size The dominant stage is multicellular All of the above None of the above

Animal Phylogeny

Body plan shifts • Symmetry – Asymmetry -> – Radial symmetry -> – Bilateral symmetry

True Tissues •

True tissues (specialization of cells) 1. Simple epithelial tissue - Sponges 2. Diploblasts (“two sprouts”) – Cnidaria • •

Ectoderm Endoderm

3. Triploblasts - Bilateralia •

Addition of mesoderm (Becomes muscle & organs)

Evolution of the Body Cavity • Coelom • Creates internal chamber for nutrient & O2 circulation • Allows organs to move independently of each other • Allows body movement via manipulation of hydrostatic pressure

Body plan shifts • Acoelomic – 3 tissue types, addition of mesoderm – No body cavity; no space between digestive tube and specialized organs – E.g. Flatworms

Body plan shifts • Pseudocoelom: incomplete lining of body cavity by mesoderm • E.g. Nematodes (round worms)

Body plan shifts • True Coelom (Eucoelom) • E.g. Annelids, Echinoderms, Chordates, Molluscs, Arthropods

Developmental differences • Cell cleavage pattern – Spiral - P – Radial - D

• Digestive tube formation – Pore becomes mouth - P – Pore becomes anus - D

• Coelom formation – As independent block of tissue - P – As eversion of endoderm - D

Diverse feeding modes

Suspension

Deposit

Mass

Fluid

Diverse food choices • Adaptations for food acquisition • • • •

Herbivores Carnivores Omnivores Detritivores

• Predators • Parasites

– Endo & ecto

Animal Phylogeny

Protostome groups

• Ecdysozoa - growth by molting (ecdysis) • Lophotrochozoa - growth by incremental additions

Defining characters

• Ecdysozoa - growth by molting (ecdysis) • Lophotrochozoa – use cilia – Lophophore: specialized feeding structure – Trocophore larva: feeding & dispersal stage

Most Animals are Protostomes • Arthropoda – Insects – Chelicerates

• Mollusca

Coelom is reduced & reinvented • Primary function: hydrostatic skeleton & space for circulating fluids

– In speciose groups, these jobs are absorbed by novel structures – Arthropods: exoskeleton & muscles; hemocoel – Molluscs: foot; visceral mass contains organs & circulates fluids

Water to Land • Protostomes made the transition (like Plants), but did so many times (many lineages) • Necessary adaptations: – – – –

Exchange gases in air vs. water Avoid desiccation Move in “high gravity” environment Once these appeared, diversification was rapid. Why?

• Protostomes move to land ~ 465 Mya, but first Vertebrates don’t invade until 360 Mya • ~ 100 My of ecological opportunity on land

Further diversification • Feeding – adaptations for food gathering or capture

• Moving – musculoskeletal systems

• Reproducing – dispersing gametes – protecting gametes & offspring – preventing desiccation

Feeding • Modification of mouthparts or appendages – Allow all types of feeding

• Ecdysis allows juveniles & adults to specialize on different foods

Moving

• Muscles & type of skeleton & appendages – Hydrostatic – Ecto – Endo

Reproduction & Life History • Sexual – External (sessile adults) or internal (mobile adults)

• Asexual (parthenogenic, fragmenting, splitting lengthwise) • Metamorphosis – Typical of taxa with sessile adults; dispersal stage

• Desiccation-resistant eggs – Amniotic OR membrane-bound (insects)

Sponges • No symmetry • No true tissues

– No nerves, no muscle, no body cavity, no skeleton; mixed layer of specialized cells

• Suspension feeders • Hermaphrodites (most are sequential)

Cnidarians • Corals, jellyfish, anemones • Radial symmetry • True Tissues! – Cnidocytes for prey capture – Gastrovascular cavity • In & out tubes are same

• Hydrostatic skeleton • Reproductive system – Gonads (testes, ovaries)

Lophotrochozoans

Ecdysozoans

Arthropoda

Roundworms