Intro and origins of verts Flashcards
What percentage of all species are vertebrates?
4%
Two main groups of vertebrates
- Non-amniotes
- Amniotes
Both share some traits that have evolved individually (e.g. birds and mammals both evolved endothermy)
What groups of animals are non-amniotes and what are their similar features?
- Bony fish, Lampreys & amphibians
- Membranes come from the digestive tracts of the female
- Tend to be aquatic
What groups of animals are amniotes and what features do they share?
- Sauropsids and synapsids
- Membranes come from the embryo: Extraembryonic
- Tend to be terrestrial
What group are Vertebrates under? and what is their sister group?
- Vertebrates are Chordates
- Urochordates (sea squirts) are the sister group withing chordates.
- Both are Deuterostomes
What is unusual about reptile phylogeny?
Not monophyletic
Examples of Convergent evolution
- Pentadactyl limbs (5 digits)
- Some have lost digits over time - horse
- Loss usually due to evolution of fast running etc
- Fusiform: Shape of porpoise, shark and ichthyosaur all simialr but evolved seperately.
Differences in amount of orders within the amniotes
- Mammals 27
- Birds 41
- Reptiles 4
- Amphibians 3
Earth’s period of fragmentation
- During this fragmentation was when birds and mammals were diversifying
- Fragmentation caused formation of many orders
- Relationship between highly diverse habitat and diversity of tetrapods
What is a possible cause for the diversification of birds and mammals?
1. Extiction of dinosaurs
- loss of main predators allowed them to move into new niches and diversify
2. Endothermy
- Able to exploit cold environments
Size variation in vertebrates
- Paedocypris (small fish) 7.9mm
- Paedophryne amauensis (frog) 7mm
- Male angler fish - sexual parasitism - 6mm (can’t live independently)
- Blue whale = largest vert
How is the female angler fish is adapted to the sexual parasitism of the male?
- Does not elicit an immune repsonse to male lacthing on
- Change in gene allows with adaptation
Why is the killifish is specialised?
- Fasted growth rate (reproduce at 17 days old)
- Live in pools that can dry up
- Eggs live in resting stage
- As soon as there’s water they rapidly grow
Mimic octopus jaw fish adaptation
mimics the octopus (lives with the octopus)
Most vertebrates are large
High energetic existence
Most verts have jaws
Gulper eel - massive modified jaw
Many vertebrates are extinct
- Tasmanian wolf (thylacine) - driven to extinction
- Chytrid fungus - causing extinctions of frogs & toads
- Possibly transmitted by humans - molecular makeup is the same across the world.
- Cave catfish - very endangered. Only found in one cave in Namibia
Verbrate phylogeny
- Deuterostomes
- Within the chordate group
- Urochordates (sea squirts) and cephalochordates also in this group
- More closely related to the urochordates than the cephalochordates
Chordate features
- Notochord
- Dorsal hollow nerve cord
- Pharyngeal gill slits - used for respiration (if retained)
- Post-anal tail
- Endostyle - structure found in pharynx. Believed to be homologous to the thyroid gland (concentrate iodine)
Have these at some point in their lifecycle
Lamprey endostyle
In larval stage is used for feeding (produces mucus), in adult form it metamorphoses into thyroid gland
What makes the vertebrates different from the inverts that have similar structures?
- Vertebrae
- Cranium
- Embryological features: Duplication of hox genes
- Development of the neural crest
Vertebrae
vertebrates are different from the inverts that have similar structures
- Usually replaces notochord (has centrum and neural canal)
- Notochord can still remain as intervertebral discs found between vertebrae
Acceptions of fully formed vertebrae
- Hagfish and lampreys: don’t have fully formed vertebrae.
- Instead have rudimentary vertebral precursors (arcualia)
- Lampreys – along body & dorsal
- Hagfishes – tail region & ventral
- Ancestor – dorsal & ventral
Cranium
vertebrates are different from the inverts that have similar structures
- Can be bony, cartilaginous or fibrous
- Vertebrae and cranium make up the endoskeleton
- Cartilaginous in early verts
Embryological features
Duplication of hox genes
vertebrates are different from the inverts that have similar structures
- Duplication of hox gene complex (homeobox genes)
- Inverts chordates only have one hox gene cluster.
- Ancestral jawless verts have 2 hox gene clusters.
- Further duplication associated with the evolutions of other features e.g. jaw
- 4 clusters = evolution of the jaw
- Bony fish (teleost) - third duplication 7 clusters (one cluster lost)
- Salmonids fourth duplication - 13 clusters (another cluster lost)
- Duplication of hox genes may add to the complexity seen in verts
Main hox gene duplication events
- Origin of verts (2 clusters)
- Jaws (4 clusters)
- Teleosts (7 clusters)
- Salmonids (13 clusters)
Development of the neural crest
vertebrates are different from the inverts that have similar structures
- Cells are migratory and multipotent - can move around the body and form in to any cell
- Responsible for new structures (especially head)
- Another germ layer - quadroblastic (4 body layers)
Possible precursors of the neural crest in invertebrates chordates
- Similar genes expressed in the 2 invertebrate chrodates during neural plate formation
- Migratory cells in tunicates form pigment cells
Placodes
vertebrates are different from the inverts that have similar structures
Give rise to complex sense organs
Unique to vertebrates
Homologs (similar genes) in invertebrate chrodates
Brain
vertebrates are different from the inverts that have similar structures
- Brain of verts is larger and has 3 parts (forebrain, midbrain & hindbrain).
- Brain of amphioxus (invert chordate) is not divided but genes are similar except the front forebrain.
Vertebrates have increased in body size, how has this effected them ?
- Can’t rely on ciliary action or diffusion
- Need organs systems to respire and process food etc
- Higher metabolic rate than non-vert chordate
- Can sustain anaerobic respiration for short periods of time
- Allows rapid movement when needed (e.g. escaping predator)
- Transition from filter feeding to active predaceous mode of life
What do Mineralised tissues contain?
- Didn’t appear early within the vertebrates
- Contain hydroxyapatite (calcium and phosphorus) - more resistant to lactic acid after anaerobic respiration
- Mineralised tissues – collagen fibres, proteinaceous tissue matrix and hydroxyapatite
Types of mineralised tissue
- Mineralised Cartilage
- Bone
- Enamel, Enameloid and Dentine
- Cementum
Mineralised Cartilage
Types of mineralised tissues
- Cartilage that’s become mineralised
- Tougher than cartilage
- 70% mineralised
Bone
Types of mineralised tissue
- Highly vascularised (can be repaired)
- Dermal bone (grown in skin).e.g. skull
- Endochondral (forms within body)
- only found in tetrapods and bony fish
- Cartilage is replaced by bone.
- 70% mineralised
Enamel, Enameloid and Dentine
Types of mineralised tissues
- Teeth
- Exoskeleton
- Dermal scales of cartilaginous fishes
- 90-96% mineralised (tougher).
- Teeth are stronger than bones.
Cementum
Types of mineralised tissues
- fastens teeth in sockets
- 45% mineralised
Origin of bone and other mineralised tissues
No mineralised tissues at the start of vertebrate evolution
- There were basic units in early verts - Odontodes (dermal). found on skin of early verts
- SIMILAR to Denticles - found in skin of sharks
Why did mineralised tissues evolve?
- Defensive structure
- & Dermal armour - ostracoderms
- Protected electroreceptors - more efficient at detecting prey.
- Storage /regulation of phosphorus and calcium.
No one really knows - above are some theories.
Earliest vertebrates
- Conodonts - toothlike structures (look like mineralised tissues) - lots of debates regarding these (fossils of teeth like structures found within the throat). Current accepted theory is that it was more convergent evolution with verts
- Ostracoderms - jawless verts, thought to be the oldest group of verts until recently.
Environment of early vertebrate evolution: Originated in marine environment, how do we know this?
- Paleontological - earliest fossil found in marine sediments.
- Comparative physiology - invert chordates (and other deuterostomes).
- Closest relatives were marine - suggests they were also marine.
- Marine and body fluids isotonic to marine water.
- Primitive verts (hagfish) marine and isotonic to marine water.
Chordate features?
- Notochord
- Dorsal, hollow nerve cord
- Pharyngeal (gill) slits
- Post-anal tail
- Endostyle
What became modified to form the jaw?
The mandibular arch (enlarged)
How many hox gene clusters are seen in ancestral jawless fish?
Two clusters
First duplication event
What does 2 hox gene duplication events give rise to?
- Evolution of the jaw
- 4 hox gene clusters
What did the third hox gene duplication event give rise to?
- Teleost fish
- 7 Clusters
- One cluster lost
What did the fourth hox gene duplication event give rise to?
- Salmonids
- 13 clusters
- another cluster lost
why are vertebrates referred to as quadroblastic?
- 4 body layers
- endoderm, ectoderm, mesoderm and neural crest
Differences in body structure between a generalised non-vert chordate and a generalised vertebrate
Vertebrates have:
- More developed heart
- Muscularised gut
- Cranuim
- Sensory organs
- Endostyle into thyroid
- Well developed muscle blocks in tail region
- Muscularised pharynx
- More developed organs
- Gill slits supported by gill bars
Evolution of mineralised tissue
Mineralised tissue
- Lampreys - unmineralised endoskeleton
- Ostracoderms (armored fish) - Exoskeleton (origin of mineralised skeleton).
- Bony fish - Mineralised endoskeleton. Retain exoskeleton (scales, Ray fins etc).
- Tetrapods - Reduction of exoskeleton in the trunk. Retained in the head (skull). Contains mineralised endoskeleton.
Age of earliest vertebrate fossil?
530 mya
How do we know that the oldest vert fossil is a vertebrate?
- No mineralised tissue
- Skull and skeletal elements made of cartilage
- Dorsal fin
- Sensory structures
