Theme A - Phylogeny

Question 1

What is phylogeny?

Answer 1

A visual representation of what is believed to be the evolutionary relationship between different organisms

Question 2

What is a dendrogram?

Answer 2

A phylogenic tree showing evolutionary descent

Question 3

What is a key aim of a dendrogram/phylogeny?

Answer 3

To show descent in the fewest number of changes/branching events

Question 4

What does the terminal point on a phylogenic tree represent?

Answer 4

A species - either living (extant) or extinct

Question 5

What does the branching point (node) on a phylogenic tree represent?

Answer 5

A speciation event, ie. when one species split into two. The node is the last common ancestor of the two following species.

Question 6

What is a clade?

Answer 6

All the descendants of a common ancestor

Question 7

What are sister clades?

Answer 7

Clades that come from the same branching point

Question 8

What is the difference between monophyletic and polyphyletic species?

Answer 8

Monophyletic species occur in the same clade whereas polyphyletic species occur in different clades

Question 9

What are the two main divisions of insects?

Answer 9

Winged (pterygota) and wingless (apterygota)

Question 10

How are winged insects divided in two groups?

Answer 10

Depending on where their wings develop:

• externally to body (exopterygota),or
• internally (endopterygota)

Question 11

What is a key reason for the diversification of insects?

Answer 11

Their different interactions with flowering plants

Question 12

What is a parasitoid? Give an example.

Answer 12

It behaves like a parasite but is not truly one.

Example: parasite wasp - lays egg on/in immature stage of another insect, which dies.

Question 13

Give an example of a visual signal used by frogs, and explain why it has evolved.

Answer 13

Foot flagging. Audio signals are ineffective due to the sound of water.

Question 14

What is speciation?

Answer 14

It occurs when a lineage splits to form two distinct species; and involves the evolution of reproductive barriers so the two no longer interbreed

Question 15

What does the biological species concept do?

Answer 15

It defines what a species is

Question 16

What is a species?

Answer 16

Organisms that interbreed (naturally) to produce viable fertile young, that are reproductively isolated from other species

Question 17

What two types of reproductive barriers can occur?

Answer 17

Pre-zygotic (before mating) and post-zygotic (after mating)

Question 18

Give three (out of five) examples of pre-zygotic reproductive barriers.

Answer 18

1. Ecological/habitat isolation - species occupy different areas geographically so are unlikely to meet
2. Seasonal/temporal isolation - mate at different times of year
3. Ethological/sexual isolation - not attracted sexually due to difference in behaviour, communication etc
4. Mechanical isolation - reproductive organs not compatible
5. Gametic isolation - fertilisation fails

Question 19

Explain the three post-zygotic reproductive barriers.

Answer 19

1. Hybrid inviable - egg fertilised but embryo dies
2. Hybrid sterile - offspring survives but is sterile
3. Hybrid breakdown - offspring survives but the fertility of their offspring is reduced

Question 20

What is allopatric speciation?

Answer 20

When two species are separated by geographic barriers, and evolve separately to such an extent that they could not longer inter-breed if they did come back together

Question 21

What is sympatric speciation?

Answer 21

Two species live in same area but do not come into contact, eg. feed on different plants or active at different times of day/night

Question 22

What is parapatric speciation?

Answer 22

There is a slight overlap in range where interbreeding occurs to form a hybrid, but most of population remains separate

Question 23

What is polyploidy?

Answer 23

A type of sympatric speciation in which there is double the number of chromosomes due to a failure during meiosis

Question 24

What is an osmoconformer? And how does this differ to an osmoregulator?

Answer 24

An osmoconformer is a marine creature that does not regulate salinity - it just lives in full strength sea water and internal fluids are in equilibrium with it.
In contrast, an osmoregulator does control the balance of salinity (osmotic pressure & ions in bodily fluids)

Question 25

How to crabs regulate osmotic pressure?

Answer 25

Water is taken in through the integument and gills, fluid is excreted as urine by the antennal gland

Question 26

What is the difference between hypo- and hyper-osmotic?

Answer 26

In hypo-osmotic, the internal osmotic pressure is less than the seawater outside;
In hype-osmotic, the internal osmotic pressure is greater (more saline) than the water outside.

Question 27

What sort of circulatory system do crabs (and other arthropods) have?

Answer 27

They do NOT have a closed circulatory system of blood. Instead there is a open system, with haemolymph fluid surrounding the internal organs.

Question 28

What is the isosmotic point (ISO)?

Answer 28

Its the point at which the internal and external osmotic pressures balance

Question 29

What is the term given for water more saline than seawater?

Answer 29

Hypersaline

Question 30

What can species that are euryhaline do?

Answer 30

Tolerate a wide range of salinity

Question 31

What is the principle of parsimony?

Answer 31

That species have evolved in the fewest steps, ie. by the simplest route

Question 32

How does competition oppose species recognition?

Answer 32

Individuals need to be different enough to stand out. If this goes too far, they may not be recognised as same species.