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Lecture 17

BIO SCI 94 Lecture Notes - Lecture 17: Choanoflagellate, Detritivore, SynapomorphyPremium

Biological Sciences
Course Code
Brad Hughes

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Cambrian Explosion-radiation of animals, 550 millions years ago
8 million-50 million extant animal species
1.4 million species described
Animal extinction accelerating from human activity
Opisthokonta-clade where animals occur
Choanoflagellates - fungi/single celled protists included
What is an Animal?
Animals eukaryotes-key traits:
Multicellularity, cells
Lack cell walls
Extensive extracellular matrix
Qtake carbon compounds from other organisms
Ingest food instead
Move under own power at one point
Animals except sponges have:
Neurons- nerve cells, transmit electrical signals to other cells
Muscle cells- change shape of body by contracting
Animals and multicellular fungi similar
Both multicellular heterotrophs
Both/digest nutrients
Animals only multicellular heterotrophs that ingest food before digesting it
Neurons connect to one another→ form nervous system
Some neurons connect to muscle cells
muscles/neurons- adaptations for efficient body movement
Animals- largest predators, herbivores, detritivores
Key consumers in ecosystem
What Key Innovations Occurred during Animal Evolution?
Fossil record inconsistent, only direct evidence of:
Animal morphology
Where they lived
When they existed
Comparative Morphology
Distinguishes shared traits and synapomorphies
Data used to
Define fundamental architecture(body plan)

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Infer which trait first appeared
Comparative Genomics
Provides information on relative similarity of genes of diverse organisms
Provides insight to phylogenetic relationship and evolutionary history
Origin of Multicellularity
Animals-monophyletic group
Animals have common ancestor
Sponges include two most basal animal lineages
Multicellularity originated from sponge like animal
Fossil Animals
Sponges-earliest animal in fossil record
First sponge- 600 mya
Morphological Evidence
Sponges and choanoflagellates share key traits
Both sessile-adults live attached to substrate
Feed in similar ways
Choanocytes- sponge feeding cells- trap/ingest food particles
Choanoflagellates sometime for colonies-group of attached individuals
Sponges once part of colonies of single celled protists
Sponge cells re-aggravate after dissociated
Some sponges have true epithelium
Epithelium-layer of tightly joined cells, covers interior/exterior surface of
Sponges diverse in size, shape, composition
Spicules- distinguish lineages
Spicules-stiff spikes of silica/calcium carbonate, provide structural
support to ECM
No unanimous agreement sponges are monophyletic group
Comparative genomic studies
Support hypothesis sponges most basal animal group
Suggest sponges paraphyletic
Support sponges have complex developmental tool kit of genes despite
morphical simplicity
Tool kit contains genes for all basic molecular processes required by animals
Cell specialization
Regulation of cell cycling/growth
Adhesion among cells, and between cells and ECM
Recognition of self and nonself
Innate immunity
Developmental signaling and gene regulation
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