Evolutionary novelty and notothenoid antifreeze glycoproteins Flashcards
What can an evolutionary novelty allow for?
The exploitation of new resources or habitats, therefore leading to adaptive evolution
‘A qualitatively new trait that triggers evolution’
A novelty is defined as…
a structure or phenotype that is both non-homologous to the ancestral state and to any other structures displayed by the same species
It is a NOVELTY (funnily enough)
Why are novelties important?
They allow for adaptive radiation, causing some organisms to become better-suited to their environment and diverge, leading to speciation
Who used the existence of evolutionary novelty to contradict Darwin’s theory of evolution? What is a famous example they gave?
Thomas Mivart, FRS:
He argued that such specific structures that are fundamental to many species could not be accidental and are proof of intelligent design.
Mammary glands of mammals; without them infants would die, how did they evolve gradually?
How many types of novelty are there? What are they?
- Implementing novelties
2. Potentiating novelties
What is an implementing novelty?
Characters that evolved in response to new ecological opportunities and are now responsible for the distinctiveness of a clade
Give examples of when implementing novelties might occur?
During island colonisation of glacial retreat
How do implementing novelties occur?
In a series of incremental changes that can be tracked over time in the ancestors of a species
Give an example of an implementing novelty.
The shell of turtles; changes were required that eventually formed the plastron, carapace, fused the vertebrae and allowed the pectoral girdle to move
Which trait in turtles can be tracked through their ancestors?
Carapace evolution
What did basal diapsids have?
Moveable ribs
The moveable ribs of basal diapsids became WHAT in Sinosaurosphargis from the Middle Triassic?
Expanded, flattened and straightened
The expanded and flattened ribs of Sinosaurosphargis became what in Odontochelys from the Late Triassic?
Even more flattened with reduced intercostal msucles
Do modern turtles have intercostal muscles?
No they degenerate in embryonic development
What changes in turtle morphology cannot be explained as implementing novelties?
Changes in scapula position, many argue this is instead potentiating
What is a potentiating novelty?
Genomic changes that occur in the early developmental programme of an organism, allowing it to better exploit an existing environment
Potentiating novelties generate the necessary genetic background that makes a trait accessible to evolution. How?
Mutations accumulate with no effect, state of non-adaptive drift in phenotype, followed by actualisation
In potentiating traits, what is actualisation?
When a final mutation pushes the organism to evolve a new trait; all the background stuff is there in the non-adaptive mutations that have accumulated, and the final mutation brings them all together and allows the trait to evolve
Are there any intermediary stages of potentiating novelties present in a species’ ancestors?
No; potentiating novelties appear ‘out of nowhere’, trait appear spontaneously generated, when actually it has been silently building in the genome for a while
What is an example of a potentiating novelty?
Antarctic notothenoid fish
At the poles what temperature does water freeze at and why?
At -2 degrees, as salinity changes the freezing point
If water freezes at -2, what does this mean for cells?
Water inside them will freeze, forming ice crystals that will rip them apart
How does synthetic antifreeze work? What is the disadvantage?
It lowers the freezing point but only works in high concentrations
Notothenoid fish have developed antifreeze glycoproteins instead. How do these work?
What are the advantages of AFGPs?
They bind the surface of an ice crystal and prevent it from growing.
They are effective at low concentrations and do not affect osmotic pressure of a cell
What is osmotic pressure?
Minimum tension across the cell that prevents the inflow of water
Basically osmotic pressure stops cells swelling and lysing
What is the structure of AGFPs in Antarctic notothenoids?
Simple glycotripeptide repeats of threonine-alanine-alanine. These are encoded as distinct molecules conserved by three residue spacers.
There is a disaccharide attached to threonine.
Thr-Ala-Ala
What are AGFPs derived from?
How do we know this?
Trypsinogen molecules
Trypsinogens and AGFPs share the same first exon and downstream sequence
What are trypsinogens?
Pancreatic digestive enzymes that cleave proteins
How do trypsinogens and AGFPs differ? Why?
Who studied this?
What does this imply?
Chen et al., 1997:
In AGFPs, Thr-Ala-Ala repeats begin just before the second exon in trypsinogen.
There is also a deletion in the central sequence and a reduction in sequence after the tripeptide repeat.
Thought these mistakes due to frame shift and replication slippage.
AGFPs evolved from several modifications to the trypsinogen sequence.
How can the evolution of AGFPs be seen as a potentiating novelty? Give 2 reasons.
- Caused by a series of genomic modifications to an existing trait. These were non-adaptive and not removed by selection, with no phenotypic effects, setting up the genetic background for AGFP evolution. Eventually a mutation would have brought these altogether, causing AGFPs to appear out of nowhere.
- AGFPs have allowed notothenoids to better-adapt to existing conditions. Perhaps notothenoids were ancestrally migrational to the poles but are now able to stay year round.
Potentiating novelties can build on existing traits and co-opt existing structures. True or false?
True
Implementing novelties can be seen as a more ‘Darwinian’ view of adaptation. Why?
Because it requires the development of a new structure for a new environment, and incremental changes can be seen in the ancestors of a species.
Potentiating novelties are more cryptic. How?
They rely on genomic changes that allow organisms to become better-adapted to existing environments. These are not observable in the ancestral phenotypes, traits simply ‘appear’
Where do they think AFGPs first evolved in notothenoid fish? Why?
The AFGP concentration in the intestinal is fluid is particularly high. Thought they evolved from trypsinogen in the digestive tract as this is particularly susceptible to freezing, as incoming food is v. cold.
