Lecture 10: Introduction to animal evolution Flashcards
Elements of biodiversity:
3 types and similarities
- Ecological Diversity
- Genetic Diversity
- Organismal Diversity
- all only linked by populations –
Features of animalia:
- eukaryote
- multicellular, held together by collagen
- heterotrophic, feed by ingestion (usually)
- muscle & nervous tissue unique to animals
- lack cell walls
- unique cell junctions:
- tight junctions
- desmosomes
- gap junctions
3 types of junction:
- tight junctions (between plasma membrane of adjacent cells, between space)
- desmosome (anchoring junction)
- gap junctions (communicating junction)
life-history features of animals
- most reproduce sexually
- life cycle dominated by the diploid stage
- small flagellate sperm fertilises a non-motile egg (heterogamete)
- blastula in early development
early embryonic development:
zygote –cleavage–> eight cell stage –cleavage–> blastula –Gastrulation–>Gastrula
Blastula:
hollow ball of cells.
inside = blastocoel
Gastrulation:
pinching inwards on itself
Gastrula:
- Endoderm inside
- Blastocoel middle layer
- ectoderm outside
- blastopore-‘entrance’
Hox genes:
special genes that regulate development in animals
Number of hox genes is correlated with
the complexity of the animal body plan
Variation in when and where Hox genes are expressed in the developing embryo is the basis
of the diversity of animal body plans
Origin of animals thoughts? brief
colonial heterotrophic flagellate similar to a choanoflagellate protozoan.
Reasons why to origin of animals
- single flagella surrounded by a collar of microvillae used for filter feeding
- single flagella consistent with the monociliate condition believed to be primitive in animals
- flagella base structure closely resembles cilia base in animals
- similar mitochondrial structure
- DNA evidence
ontogeny reflects
phylogeny
how have evolutionary relationships among animals been concluded?
-Paleontological evidence appearance in the fossil record -Anatomical similarity shared, derived homologous structures -Developmental similarity patterns of cell division and embryonic stages -Biochemical similarity DNA, RNA and protein similarity
Traditional view of animal evolution is based on..
BODY PLANS
- True tissues formed following gastrulation
- Symmetry
- Presence of a body cavity or coelom
- Pattern of coelom development
Gastrulation results in
..at least two tissue layers (endoderm and ectoderm)
- Separates Parazoa (inc. sponges) from Eumetazoa
- True tissues enable specialisation and organ development
Radial and bilateral symmetry:
Separates Radiata (jellyfishes) from Bilateria
- Radiata have a top/bottom or oral/aboral side, bilateria have anterior/posterior and dorsal/ventral sides
- Radiata are diploblastic, Bilateria triploblastic
- Bilateral symmetry associated with cephalisation and active lifestyle
Evolution of body cavities:
Acoelomate
pseudocoelomate
coelomate
coelomate
(e.g. earthworms Annelida)
coelom lined with mesoderm
Acoelomate
(e.g. flatworms Platyhelmithes)
solid body between digestive tract and outer body wall
lack digestive tract or incomplete without anus
pseudocoelomate
(e.g. roundworms Nematoda)
coelom not completely lined with mesoderm
Functions of the body cavity:
protection
allows organ growth
allows movement (hydrostatic skeleton)
Coelom development in protostomes:
(Mollusks, annelids, arthropods)
- eight cell stage: spiral & determinate
- Schizocoelous: solid masses of mesoderm split to form coelom
- mouth develops from blastopore
