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Summary Organisme Dier Campbell
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- Organisme Dier
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Campbell BO DIER22.3
Homology: similarity resulting from common ancestry -> fore-arms same bone
arrangements
mammals = homologous structures
Vestigial structures remnants of features that served a function in organism’s
ancestors.
Homologies from common can be shown by ancestors with evolutionary tree,
relative timing.
Convergent evolution: distantly organisms can resemble one another for a
different reason -> independent evolution of similar features in different lineages.
Analogy: similar function, but not common ancestry.
26.2
Morphological divergence between related species can be great and their genetic
divergence small (or vice versa). Convergent evolution occurs when similar
environmental pressures and natural selection produce similar (analogous)
adaptations in organisms from different evolutionary lineages.
Analogous structures that arose independently = homoplasies.
Distantly related species have different bases at many sites and may have
different lengths, because of insertions and deletions that accumulate over long
periods of time.
Molecular homoplasies: organisms that don’t appear to be closely related, the
bases that their otherwise very different sequences happen to share may simply
be coincidental matches.
Phylogeny now is molecular genetics.
34.1
Chordates (vertebrates + cephalochordates + urochordates + hagfishes
(Myxini)). Characteristics:
1. Notochord: skeletal structure, between digestive tube and nerve chord, large
fluid-filled cells
encased in fairly stiff, fibrous tissue -> skeletal support. Most vertebrates a
more complex, jointed
skeleton develops around ancestral notochord -> retains only remnants of
embryonic notochord.
2. Dorsal, hollow nerve chord: nerve chord develops from a plate of ectoderm
that rolls into a tube
located dorsal to the notochord, develops into central nervous system.
3. Pharyngeal slits of clefts: digestive tube from mouth to anus, just posterior to
mouth is pharynx.
The clefts develop into slits that open to the outside of the body -> water
entering the body to exit
without passing entire digestive tract -> suspension-feeding devices in in-
vertebrates.
In vertebrates modified for gas exchange = gill slits. In tetrapods pharyngeal
clefts do not develop
into slits (development parts ear + head & neck).
4. Muscular post-anal tail: posterior to anus -> but many species reduces during
embryonic
development.
,Cephalochordata (lancetvisjes): as larvae notochord + dorsal, hollow nerve
chord + numerous pharyngeal slits + post-anal tail. Filter feeder, seawater to
pharyngeal slits, not so much to do with gas exchange because across external
body surface. Coordinated contraction of muscles arranged like rows of <<<<
along sides of the notochord -> serial arrangement of muscles is evidence of the
lancelets segmentation -> develop from blocks op mesoderm = somites.
Urochordata (tunicates): larval stage has chordate characters. Uses tail
muscles and notochord to swim through water (light- and gravity-sensitive cells).
Metamorphosis on substrate -> many chordate characters disappear. Water
passes through pharyngeal slits.
Vertebrate brain is elaboration of an ancestor structure similar to the lancelets
simple nerve cord tip.
34.2
Craniates: possess two or more sets of Hox genes, other important genes
duplicated -> genetic complexity. Neural crest (unique): a collection of cells near
the dorsal margins of the closing neural tube in an embryo -> disperse
throughout the body -> variety of structures: teeth + inner layer of skin + facial
region + several types of neurons.
Aquatic craniates pharyngeal clefts evolved into gill slits (sucking food +
facilitates gas exchange). Craniates are more active, higher metabolic rate +
extensive muscular system, heart with at least two chambers + red blood cells
with hemoglobin + kidneys.
- Myxini (slijmprikken): swim with segmental muscles to exert force against
notochord, live marine,
covered with slime glands.
34.3
Vertebrates: branch of craniates, gene duplication Dlx transcription factors ->
nervous system + skeleton. Most species the vertebra enclose the spinal cord ->
taken over mechanical roles of notochord.
- Petromyzontida (prikken): aquatic environments, parasites, jawless, skeleton
made of cartilage, no
collagen, main axial skeleton.
What initiated mineralization of the skeleton? Hypothesis: transition feeding
mechanisms, first filter feeders, after that conodont dental elements -> became
predators -> mineralization begun in the mouth, later incorporated into
protective armor.
34.4
Gnathostomata: jawed vertebrates: everything from sharks/ray-finned fishes.
Jaws evolved by modification of skeletal rods that previously reported pharyngeal
slits -> no longer needed for suspension feeding + additional duplication Hox
genes (4 pair) + whole genome duplicated + bigger forebrain + lateral line
system (aquatic gnathostomes).
- Chondrichthyans (sharks, rays): skeleton predominantly of cartilage, oil in
liver to prevent sinking,
often suspension feeders, shark intestine = spiral valve, acute senses, eggs
, fertilized internally.
Oviparous (lay eggs) + ovoviviparous (fertilized eggs in oviduct) + viviparous
(young develop in
uterus -> yolk sac placenta).
- Osteichthyans (Actinopterygii, Actinistia & Dipnoi) (ray-finned fishes and
lobe-fins):
ossified endoskeleton, breath by drawing water over four/five pairs of gills
covered by operculum,
control sinking with swimbladder, most are oviparous
34.5
Tetrapods: limbs instead of pectoral and pelvic fins + head separated with neck
+ bones pelvic girdle (hind legs attached) fused to backbone, no gills, pharyngeal
clefts rise to parts of ears, certain glands.
Origin tetrapods: lobe-fins in shallow, oxygen poor water used lungs to breathe
air -> used fins to move across muddy bottom-> modification of pre-existing
body plan.
- Amphibia: salamanders, frogs and urodeles (secondary legless), can life on
land and in water, but
not dual (larve-adult), in damp habitats -> skin for gas exchange, fertilization
external, lay eggs in
moist environments on land, eggs lack shell (dehydrate quickly), also some
ovoviviparous and
viviparous species.
34.6
Amniotes: tetrapods who lays amniotic eggs: 4 specialized membranes: amnion
+ chorion + yolk sac + allantois = extraembryonic membranes. Amnion is
hydraulic shock absorber, other membranes for gas exchange, transfer stored
nutrients and waste storage -> key evolutionary innovation for terrestrial life ->
reducing dependence of tetrapods on aquareous environments for reproduction,
shells eggs are calcareous/leathery and can be both flexible or inflexible -> slows
dehydration
Other adaptations for living on the land: rib cage to ventilate their lungs
- Reptile: scales contain keratin, lay shelled eggs on land, fertilization internally,
viviparous, regulate
body temperature by behavioural adaptations -> ectothermic (absorb external
heat as main source
of body heat) (birds are endothermic).
- Birds: weight saving modifications: lack urinary bladder, gonads small (only
increase in size during
breeding season), teethless, feathers made of beta-keratin, beneficial for
hunting and scavenging,
great migrate distance, ready escape ground predators, complex behaviours.
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