speciation

Question 1

what is a species?

Answer 1

a population of reproducing organisms that is isolated from other populations

Question 2

what are some exceptions to the species definition?

Answer 2

• cannot apply it to prokaryotes and eukaryotes that are not strictly sexual
• it is impossible to use with extinct organisms
• difficult with bacteria and archaea that have horizontal gene transfer

Question 2

what is speciation

Answer 2

the way in which spsecies can appear

Question 2

how can species appear in time?

Answer 2

along a lineage, for example humans/chimps and our common ancestor

Question 2

allopatric speciation

Answer 2

where populations of a species become geographically isolated by a barrier, such as a mountain range or a body of water, leading to reproductive isolation and the formation of new, distinct species.

Question 2

Who defined the Biological Species Concept (BSC)?

Answer 2

The concept was defined by Mayr and Dobzhansky.

Question 2

What is the definition of a species?

Answer 2

A species is a population of reproducing organisms that is isolated from other populations.

Question 2

What is the essential factor for defining a species?

Answer 2

The lack of interbreeding, or reproductive isolation, is the essential factor.

Question 2

Why is the Biological Species Concept (BSC) impossible to apply to extinct organisms?

Answer 2

It is impossible to test the reproductive behaviour and interbreeding capabilities of fossilised organisms.

Question 3

What issue makes the Biological Species Concept difficult to apply to bacteria and archaea?

Answer 3

The process of horizontal gene transfer complicates the concept of reproductive isolation.

Question 4

The Biological Species Concept has problems when applied to prokaryotes and eukaryotes that are not strictly _____, such as most plants.

Answer 4

sexual

Question 5

How is speciation generally defined in an evolutionary context?

Answer 5

It is the evolution of strong, genetically based isolating barriers that prevent gene exchange between populations.

Question 6

What does the term ‘allopatric’ mean in the context of speciation?

Answer 6

It means ‘other homeland’ (from ‘allos’ = other, ‘patra’ = homeland).

Question 7

What is the primary requirement for allopatric speciation to occur?

Answer 7

It requires the physical isolation of populations by a geographic barrier.

Question 8

What is the effect of the geographic barrier on gene flow in allopatric speciation?

Answer 8

Physical isolation completely prevents gene flow between the populations.

Question 9

In allopatric speciation, reproductive isolation evolves as a _____ of the populations’ divergent evolution.

Answer 9

byproduct

Question 10

Does allopatric speciation require different selection pressures in the isolated zones?

Answer 10

No, it does not necessarily require different selection pressures to lead to speciation.

Question 11

What species on either side of the Grand Canyon exemplifies allopatric speciation?

Answer 11

Two different species of antelope squirrels are found on either side.

Question 12

What does the term ‘sympatric’ mean in the context of speciation?

Answer 12

It means ‘same homeland’ (from ‘sym’ = same, ‘patra’ = homeland).

Question 13

How does sympatric speciation differ from allopatric speciation regarding geography?

Answer 13

Sympatric speciation occurs without any geographical isolation between the diverging groups.

Question 14

What is the state of the diverging groups at the beginning of sympatric speciation?

Answer 14

The process begins with complete genetic mixing, as the incipient species are in physical contact.

Question 15

What is the most common mechanism driving sympatric speciation?

Answer 15

The most common scenarios involve disruptive selection, driving a population in two different directions.

Question 16

In sympatric speciation driven by disruptive selection, what is the fitness of hybrids between the two subpopulations?

Answer 16

Hybrids between the subpopulations suffer from reduced fitness.

Question 17

Why is sympatric speciation considered highly debated and difficult in animals?

Answer 17

Genetic recombination breaks up co-adapted gene groups when incipient species interbreed, slowing or preventing speciation.

Question 18

Under what conditions do theoretical models show sympatric speciation can occur?

Answer 18

It occurs only under restrictive and biologically unrealistic conditions.

Question 19

In which group of organisms can the effects of sympatric speciation be easily shown?

Answer 19

Plants can easily show the effects of sympatric speciation.

Question 20

What is allopolyploid speciation?

Answer 20

It is when two sympatric species form a hybrid, which then doubles its chromosome number to create a new, reproductively isolated species.

Question 21

Polyploidy in plants, a process involving the doubling of chromosome numbers, is considered a type of _____ speciation.

Answer 21

sympatric

Question 22

What is the immediate consequence of an organism doubling its chromosome number through polyploidy?

Answer 22

The resulting organism cannot sexually reproduce with others of its original species.

Question 23

What ability allows a new plant formed by polyploidy to establish a new lineage?

Answer 23

The ability of plants to reproduce by selfing allows it to reproduce with itself.

Question 24

What characteristic of plants allows polyploid speciation to take place more readily?

Answer 24

Plants exhibit greater genetic, physiological, and developmental flexibility.

Question 25

What change in behaviour has been observed in the Blackcap (Sylvia atricapilla) population over the last 30 years?

Answer 25

Some individuals have begun over-wintering in the UK instead of the traditional location of Spain.

Question 26

What differences have emerged between the UK-wintering and Spain-wintering Blackcap populations?

Answer 26

There are strong signs of genetic and morphological differences between them.

Question 27

What term describes the mating behaviour of Blackcaps, where UK birds mate with UK birds and Spanish with Spanish?

Answer 27

This is called 'assortative mating'.

Question 29

What is the likely isolating mechanism driving the divergence of Blackcap populations?

Answer 29

The isolation is likely due to temporal isolation, specifically the arrival time on the breeding grounds.

Question 30

What is the relationship between the Hooded Crow and the Carrion Crow in terms of reproduction?

Answer 30

Although they have different distributions, they can hybridise where their ranges meet.

Question 31

What is notable about the 83 base differences found between Hooded and Carrion Crows?

Answer 31

81 of those differences are located within the same genetic region.

Question 32

What physical trait is thought to be an important factor in the divergence of Hooded and Carrion Crows?

Answer 32

The difference in their colour is considered a potentially important factor.

Question 33

Besides selection, what random statistical effects can lead to speciation when combined with long isolation?

Answer 33

Genetic drift and population bottlenecks can lead to speciation.

Question 34

Speciation is not an adaptation but merely an?

Answer 34

event or a consequence of particular conditions

Question 35

While random effects can cause speciation, what is the only evolutionary process that consistently creates adaptation?

Answer 35

Natural selection is the only way of consistently creating adaptation.

Question 36

Why is speciation often described as an 'accident' that takes a long time?

Answer 36

Partly because natural selection is often not directly involved in the creation of reproductive isolation.

Question 37

What is 'reinforcement' in the context of speciation?

Answer 37

It is the process where natural selection strengthens reproductive isolation to prevent the production of unfit hybrid offspring.

Question 38

Under what specific circumstances does reinforcement occur?

Answer 38

It occurs when previously geographically separated populations meet again in secondary contact and hybridise.

Question 39

Why does natural selection favour the reinforcement of species differences?

Answer 39

Natural selection never favours the production of unfit offspring, so it acts to prevent wasteful matings.

Question 40

Individuals who avoid mating with a divergent population have higher fitness because they do not waste gametes producing sterile or _____ hybrid offspring.

Answer 40

inviable

Question 41

What is the ideal setting to test for the occurrence of reinforcement?

Answer 41

Hybrid zones, where the two diverging populations meet and interbreed, provide an ideal setting.

Question 42

How can scientists test if reinforcement is occurring in a hybrid zone?

Answer 42

They compare individuals within the hybrid zone (sympatric) to those outside it (allopatric).

Question 43

If reinforcement is taking place, how should reproductive isolation differ between sympatric and allopatric individuals?

Answer 43

Individuals in the hybrid zone (sympatric) should exhibit stronger reproductive isolation.

Question 44

When two hybridising groups meet, what is the likely outcome if there is lots of gene flow between them?

Answer 44

The likely outcome is the fusion of the two groups into one.

Question 45

When two hybridising groups meet, what is the likely outcome if there is some gene flow leading to a significant loss of fitness?

Answer 45

This situation will likely lead to the reinforcement of isolation.