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Summary of all lectures EZO31306 Vertebrate Structure and Function
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Summary of all lectures of Vertebrate Structure and Function (EZO-31306)
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Vertebrate Structure and Function (EZO31306) SummaryLecture 1: Introduction
Key questions in vertebrate biology
How and where did the vertebrates evolve?
What are the phylogenetic relationships among vertebrates?
How are vertebrates build?
Why are they build as they are?
o How do they develop?
o How do they function?
- Taxonomical approach: use phylogenetic tree: describe biology of groups of
vertebrates
- Systems approach: compare organ systems at different structural levels. Show how
different groups have solved comparable problems.
- Regional approach: compare structures and functions in certain regions such as the
head.
Importance of vertebrates: more than 200
different cell types have been distinguished.
There are about 60.000 vertebrate species.
Most species rich phylum after:
- Arthropoda: 1-30 million
- Molluscs: 100.000
Vertebrates:
- Fish: 31.300 (Lamprey, sharks, rays,
bony fishes and other)
- Amphibians: 6.400
- Reptiles: 19.000 (birds, crocodiles and
others)
- Mammals: 5.500
Evolutionary theory: all living organisms are
descendants from a single ancestor. Evolution
occurs through natural selection. Principles:
variability, heritability, mortality and selection.
Genes determine the
morphology of an
individual. Due to this
morphology, individuals
have a certain
performance in their
life. These different
performances lead to
selection, because
some performances of
individuals are more
advanced than others.
,Cladistics: phylogeny and technics
Principle:
1. All groups (taxa) have one common ancestor
2. Organisms with the same ancestry are grouped together, based on shared derived
characters: synapomorphic characters
3. Determination of ancestral state by outgroup comparison: plesiomorphic characters
4. Characters found in only one specific group are called (aut)apomorphic characters.
These characters contain no information!
Method:
Character scores, based on anatomy, molecular and behaviour
Phylogeny reconstruction based on: outgroup comparisons, algorithm (parsimony,
maxium likelihood)
Phylogenetic tree/cladogram (consists of dichotomies)
Monophyletic: most recent common ancestor with all its descendants (=clade, taxon)
Paraphyletic: most recent common ancestor, with only a part of the descendants (only a
minority is missing.
Polyphyletic: groups that do not include the common ancestor (a lot is missing from the tree).
Homology: characters that are equal in general morphology, phylogeny and
ontogeny due to shared ancestry.
Analogy: characters with a similar function. For example the wings of a fly, a moth
and a bird are analogous, because they developed independently as adaptations
to a common function: flying. Or gills in fish and lungs in humans for the function of
breathing.
Homoplasy: characters that look similar, but can’t be considered homologous, due
to convergent evolution or parallel evolution or reversal.
- Isometric growth: has the same dimensions. The leg always has the same comparative
length compared with the rest of the body. But this growth leads to a reduced surface-volume
ratio, because the inside grows in the 3rd power and the skin in the 2nd power. This means
that new structures for gas exchange are needed. Solution for this is invagination
(lung/intestine) and implementation of a circulatory system.
- Allometric growth: relative changes in the body. This is sometimes necessary to stay alive.
Adult forms (morphologies) are the result of development:
Biogenetic law: ontogeny recapitulates phylogeny. Each step is an addition to an initial step.
Development and growth repeat evolutionary history. New forms are the result of addition.
,Embryos are all different. They are not the same due to the influence of the environment.
Selection also takes place in early stages of development. This leads to changes in
morphology.
Heterochrony: variation in the start and/or duration of the development of a character
(compared to other characters).
- Frogs: the heart and eye are the first developed. The forelimbs are the last things
developed. In opposums the forelimbs are one of the first things developed. The reason for
this is that opposums are recipiels (pouch animals): they have to crawl from the vagina to the
pouch, where it further develops.
There is no need to change the organs, but there is need to change the timing.
Paedomorphic (resembles earlier stage). Adult stages that resemble a juvenile stage.
1). Progenesis: the descendant stops earlier in development compared to the ancestor, but
has the same growth rate.
2). Neoteny: the descendant has a slower growth rate than ancestors and does not reach the
adult stage. This happens for example in axolotls: it remains in the juvenile stage, but is
reproductive.
3). Post-displacement: the descendant has the same growth rate as the ancestor, but it starts
later, so doesn’t reach the same end point. For example: the missing of the front limbs in a
certain salamander.
A = ancestor D = descendant.
Peramorphic (further developed than ancestors)
1). Hypermorphosis: the descendant has the same growth patterns as the ancestor, but it
grows longer. The ancestor had a small skull, but changed to a bigger one.
2). Acceleration: The descendant has a faster growth rate as the ancestor, so reaches the
adult stage, when it is larger. For example: small dogs vs big dogs.
3). Pre-displacement: the descendant starts growing earlier than the ancestor, which makes
sense for the recipiels: they need to develop their forelimbs, to make sure that they can crawl
to the mom’s pouch.
, Lecture 2: Origin of Chordates
Eukarya: large number of unicellular organisms and two groups with multicellular organisms:
plants and animals fungi.
Ophistokonta Metazoa:
- Diplobastic: have an ectoderm
and endoderm
- Triploblastic: have an ectoderm,
endoderm and mesoderm.
Protosome: blastopore becomes
the mouth, anus form secondarily.
Deuterostome: blastopore is the
anus (there is a back front
inversion). The mouth forms
secondarily.
Deuterostomia: 2 groups (+
chordates):
1). Echinoderms (yellow lines in
pictures): starfish, sea urchins, sea
cucumbers
2). Hemichordata (red lines): half
chordates with synapomorphic
characters: tripartite body:
proboscis, collar and a trunk.
- Pterobranchs (red lines in picture) (subgroup of hemichordata): synapomorphic characters:
collar transformed into feeding arms. A U-shaped trunk, anus near feeding arms, a collar
ganglion and a few pharyngeal slits.
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