Evolutionary novelty and notothenoid antifreeze glycoproteins

Question 1

What can an evolutionary novelty allow for?

Answer 1

The exploitation of new resources or habitats, therefore leading to adaptive evolution

‘A qualitatively new trait that triggers evolution’

Question 2

A novelty is defined as…

Answer 2

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)

Question 3

Why are novelties important?

Answer 3

They allow for adaptive radiation, causing some organisms to become better-suited to their environment and diverge, leading to speciation

Question 4

Who used the existence of evolutionary novelty to contradict Darwin’s theory of evolution? What is a famous example they gave?

Answer 4

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?

Question 5

How many types of novelty are there? What are they?

Answer 5

1. Implementing novelties

2. Potentiating novelties

Question 6

What is an implementing novelty?

Answer 6

Characters that evolved in response to new ecological opportunities and are now responsible for the distinctiveness of a clade

Question 7

Give examples of when implementing novelties might occur?

Answer 7

During island colonisation of glacial retreat

Question 8

How do implementing novelties occur?

Answer 8

In a series of incremental changes that can be tracked over time in the ancestors of a species

Question 9

Give an example of an implementing novelty.

Answer 9

The shell of turtles; changes were required that eventually formed the plastron, carapace, fused the vertebrae and allowed the pectoral girdle to move

Question 10

Which trait in turtles can be tracked through their ancestors?

Answer 10

Carapace evolution

Question 11

What did basal diapsids have?

Answer 11

Moveable ribs

Question 12

The moveable ribs of basal diapsids became WHAT in Sinosaurosphargis from the Middle Triassic?

Answer 12

Expanded, flattened and straightened

Question 13

The expanded and flattened ribs of Sinosaurosphargis became what in Odontochelys from the Late Triassic?

Answer 13

Even more flattened with reduced intercostal msucles

Question 14

Do modern turtles have intercostal muscles?

Answer 14

No they degenerate in embryonic development

Question 15

What changes in turtle morphology cannot be explained as implementing novelties?

Answer 15

Changes in scapula position, many argue this is instead potentiating

Question 16

What is a potentiating novelty?

Answer 16

Genomic changes that occur in the early developmental programme of an organism, allowing it to better exploit an existing environment

Question 17

Potentiating novelties generate the necessary genetic background that makes a trait accessible to evolution. How?

Answer 17

Mutations accumulate with no effect, state of non-adaptive drift in phenotype, followed by actualisation

Question 18

In potentiating traits, what is actualisation?

Answer 18

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

Question 19

Are there any intermediary stages of potentiating novelties present in a species’ ancestors?

Answer 19

No; potentiating novelties appear ‘out of nowhere’, trait appear spontaneously generated, when actually it has been silently building in the genome for a while

Question 20

What is an example of a potentiating novelty?

Answer 20

Antarctic notothenoid fish

Question 21

At the poles what temperature does water freeze at and why?

Answer 21

At -2 degrees, as salinity changes the freezing point

Question 22

If water freezes at -2, what does this mean for cells?

Answer 22

Water inside them will freeze, forming ice crystals that will rip them apart

Question 23

How does synthetic antifreeze work? What is the disadvantage?

Answer 23

It lowers the freezing point but only works in high concentrations

Question 24

Notothenoid fish have developed antifreeze glycoproteins instead. How do these work?

What are the advantages of AFGPs?

Answer 24

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

Question 25

What is osmotic pressure?

Answer 25

Minimum tension across the cell that prevents the inflow of water

Basically osmotic pressure stops cells swelling and lysing

Question 26

What is the structure of AGFPs in Antarctic notothenoids?

Answer 26

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

Question 27

What are AGFPs derived from?

How do we know this?

Answer 27

Trypsinogen molecules

Trypsinogens and AGFPs share the same first exon and downstream sequence

Question 28

What are trypsinogens?

Answer 28

Pancreatic digestive enzymes that cleave proteins

Question 29

How do trypsinogens and AGFPs differ? Why?

Who studied this?

What does this imply?

Answer 29

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.

Question 30

How can the evolution of AGFPs be seen as a potentiating novelty? Give 2 reasons.

Answer 30

1. 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.
2. 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.

Question 31

Potentiating novelties can build on existing traits and co-opt existing structures. True or false?

Answer 31

True

Question 32

Implementing novelties can be seen as a more ‘Darwinian’ view of adaptation. Why?

Answer 32

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.

Question 33

Potentiating novelties are more cryptic. How?

Answer 33

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’

Question 34

Where do they think AFGPs first evolved in notothenoid fish? Why?

Answer 34

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.