Lecture 5 - Animals (Midterm 3)

Closest sister group to animals?

Choanoflagellates (protists)

On a phylogenetic tree, what kind of a group are animals?

Monophyletic

Which traits do all animals have?

1. Multicellular eukaryotes

   • No cell walls

   • Extracellular matrix (ECM) - proteins specialized for cell-cell adhesion and communication

2. Heterotrophs - organisms that can’t produce their own food

   • food ingested rather than absorbed

3. All animals move (on their own power at some point in their life)

4. Neurons (nerve cells)

5. Muscle cells (with the exception of sponges)

Extracellular matrix (ECM)

• proteins specialized for cell-cell adhesion and communication

• ALL animals have this

Do smaller animals have larger or smaller genomes/less or greater number of genes than humans?

It’s more complicated than that; not a yes/no question

Sponge-first hypothesis

sponges are the most ancient lineage of animals (branched off first during the diversification of animals)

Molecular evidence for sponge-first hypothesis

• Evidence: Sponges have tool–kit genes necessary for all the basic molecular processes required by animals

  • Cell-cell adhesion

  • cell-ECM adhesion

Morphological evidence for the sponge-first hypothesis

• Evidence: sponges share characteristics with choanoflagellates (who are sister taxa to animals)

1. Sponges and choanoflagellates are benthic

   1. Benthic - living at the bottom of aquatic environments

2. Sponges and choanoflagellates are sessile

   1. Sessile - not capable of moving to another location, adults are permanently attached to a substrate rather than moving freely

3. Their feeding cells are similar in structure and function

   1. Both are suspension feeders

   2. Their specialized feeding cells generate a current using flagella, trapping particles from water flow

Benthic

living at the bottom of aquatic environments

Sessile

not capable of moving to another location, adults are permanently attached to a substrate rather than moving freely

Do ALL animals have tissues?

No; sponges do NOT have tissues

How are animals other than sponges distinguished?

If they are diploblasts or triploblasts

Diploblasts

animals whose embryos have 2 types of tissues (“two-buds”)

• Ctenophora (comb jellies), Cnidaria (jellyfish)

• germ layers:

  • Ectoderm - outermost germ layer in animal embryos (Responsible for outer covering and nervous system)

  • Endoderm - innermost germ layer in animal embryos (Responsible for digestive tract and organs that connect to it (liver, lungs))

Triploblasts

animals whose embryos have 3 types of tissue (“three-buds”)

• Ectoderm - outermost germ layer in animal embryos (Responsible for outer covering and nervous system)

• Endoderm - innermost germ layer in animal embryos (Responsible for digestive tract and organs that connect to it (liver, lungs))

• Mesoderm - middle germ layer in animal embryos (Responsible for circulatory system, muscles, bone, blood, most internal organs)

Mesoglea

gelatinous material that connects the germ layers of animal embryos

Why do some diploblasts have mesodermal cells?

• Diploblasts have genes coding for the COMPONENTS of mesoderm cells, but NOT the specification genes present in triploblasts → due to convergent evolution and gene homology

Why can diploblasts change the shape of their bodies to move despite not having a mesoderm for muscles?

muscle-related genes evolved at different times across animals, but they still perform similar functions → homology (shared ancestry) and convergent evolution

Bilateral symmetry

Body plan with only one plane of symmetry

• found mainly in triploblasts

Radial symmetry

Body plan with at least 2 planes of symmetry

• Centophores, cnidarians, sponges

• Evolved independently of bilateral symmetry

Which came first, radial or bilateral symmetry?

Radial (Evolved independently of bilateral symmetry )

Bilaterians

triploblastic, bilateral symmetric animals

Explain this image

Figure 30.7 - Genetic evidence for homology in bilateral symmetry in cnidaria and bilaterians

• Experiment: Gene expression patterns in the Nematostella larva (cnidaria) and the mouse (bilaterian) → similar pattern of gene expression for bilateral symmetry in both organisms

• Conclusion - some elements of bilateral symmetry evolved before the split between cnidarians and bilaterians → bilateral symmetry in sea anemones is homologous to bilaterians

Difference between the nervous systems of bilateral symmetry and radial symmetry

Radial symmetry - nerve net (network of neurons throughout the body)

Bilateral symmetry - central nervous system (neurons clustered into ganglia and nerve cords, forming a brain)

Cephalization

the evolution of a head

Coelom

• body cavity that provides a space for the circulation of oxygen and nutrients (derived from mesoderm tissues)

Coelomates

bilaterians who have a coelom completely lined with mesodermally derived tissue

Acoelomates

bilaterians that have no coelom

Pseudocoelomates

bilaterians whose coelom is only partially lined with mesoderm-derived tissues

Which germ layer is the skin from?

ectoderm

Which germ layer are muscles and organs from?

Mesoderm

Which germ layer is the gut from?

endoderm

• Bilaterian coelomates (2 subgroups)

• Protostomes - lineage of bilaterian coelomates, where the mouth developed before the anus in the embryo

• Deuterostomes - lineage of bilaterian coelomates, where the anus developed before the mouth in the embryo

gastrulation

When the germ layers form (cells move from the surface to the interior of the embryo)

Vertebrates

animals with a segmented backbone (monophyletic group)

Invertebrates

animals without a backbone (most animals)

NOT a monophyletic group

Reasons for adaptive radiation

1. Higher oxygen levels

2. Higher quality food sources

3. Evolution of predation/predators

4. Animals created new niches for themselves as they diversified

5. Modified genes, modified bodies

What influenced the diversification of sensory organs

The evolution of a cephalized body

Examples of diversification of sensory organs

5 senses

• magnetic field (helps animals use earth’s magnetic field to help with navigation)

• electric field (aquatic predators sensitive to electric fields → detects electrical activity in passing prey)

• barometric pressure (birds detecting changes in air pressure → birds avoid storms)

Detritivores

An organism whose diet consists mainly of dead organic matter

Herbivores

An animal that eats primarily plants or algae

Carnivores

An animal whose diet consists predominantly of meat/other animals

Omnivores

An animal whose diet regularly includes a variety of organisms, including plants, animals, etc

Endoparasite

A parasite that lives inside the host’s body

Ectoparasites

A parasite that lives on the outer surface of the host’s body

4 feeding strategies of animals

1. Suspension feeders (captures food by filtering out particles floating in the water or air)

2. Deposit feeders (ingests organic material that has been deposited within a substrate or on its surface)

   • ex) sea cucumber uses tentacles to mop up food from sea floor

3. Fluid feeder (sucks or mops up liquids)

4. Mass feeders (takes chunks of food into their mouth)

3 types of animal skeletal systems

1. Hydrostatic skeletons - body wall surrounding a fluid/soft tissue (found in worms)

2. Endoskeletons - bones/structures inside the body

3. Exoskeleton - bones/structures outside of the body

Diversification of limbs of animals

1. Lobe-like limbs (small lobes)

2. Jointed limbs

3. Parapodia

4. Tube feet

5. arms and tentacles

Explanation for animal appendage homology?

All animal appendages have some degree of genetic homology, even if the limbs themselves evolved independently in different lineages

Diversification of animal reproductive strategies

1. Asexual reproduction

2. Sexual reproduction

3. Internal fertilization

Viviparous

Animals that give birth to live young

Oviparous

Animals that deposit fertilized eggs (insects, birds)

Parthenogenesis

A form of asexual reproduction where offspring develop from unfertilized eggs