Evolution: Lecture 5

Question 1

What is the origin of species?

Answer 1

The origin of species can be referred to as the hinge point between macro and micro evolution.

Question 2

What do we get from the origin of species?

Answer 2

The Origin of Species is a fundamental part of understanding the nature of life on earth.

Question 3

Questions posed in the Origin of Species?

Answer 3

Where the many species on earth come from and why there are so many different species.

Question 4

What is a species?

Answer 4

It is difficult to get an actual universal definitions.

Ideas include:

• Fundamentally different life on earth
• Building blocks of biodiversity

Question 5

Morphological species concept?

Answer 5

It is based on morphological similarity, and historically the most commonly used concept.

Begs the question of how much difference is enough?
- The answer is very subjective
- We can have different gene pools that have different fixed alleles in their populations, therefore populations within species can be genetically different.

Question 6

What else can be used?

Answer 6

Molecular sequence similarity no also used, which is the act of comparing DNA sequences.

• presents a similar problem with scientists’ judgements being subjective.

Question 7

Biological species concept?

Answer 7

Has two different components:

• Inter-fertility
• Reproductive isolation

Typically only works for sexual species, and not applicable to everything - usually the most useful concept. It is also very hard to apply to fossils.

Question 8

What is inter-fertility?

Answer 8

Populations that interbreed to
produce fertile offspring.

Main question: can a set of organs reproduce sexually to produce viable, fertile offspring.

Question 9

What does inter-fertility include?

Answer 9

Two populations within one species or two separate species. If they readily interbreed, they’re the same biological species.

Question 10

What is reproductive isolation?

Answer 10

Species that do not normally successfully interbreed in nature with other species, meaning no/few ‘Hybrids’.

They are not the same species if they are unable to produce viable offspring.

Question 11

What are hybrids?

Answer 11

One parent from each population or species.

Question 12

Summary of the biological species concept?

Answer 12

Inter-fertility: ability to interbreed, groups biological species

Reproductive isolation: A set of barriers that exist between different species that make them unable to breed and produce healthy offspring. Separates different biological species.

Question 13

What is speciation?

Answer 13

The making of new species.

Question 14

Clade agenesis?

Answer 14

When one species effectively becomes two.

Question 15

Reproductive barriers?

Answer 15

Intrinsic things about barriers involved that mean that the separate biological species cannot easily interbreed.

• They involve the biological features of the two biological species.

Question 16

What do reproductive barriers do?

Answer 16

inhibit gene flow between populations, allowing for
evolutionary divergence.

Question 17

What is a speciation event?

Answer 17

Two populations diverging means they are evolving/experiencing evolutionary change. They have to include the evolution of reproductive barriers. Speciation events occur when one species becomes two.

Question 18

What are pre-zygotic barriers?

Answer 18

Those that act before fertilization, preventing it

Question 19

What are post zygotic barriers?

Answer 19

Those that act after fertilization, preventing a zygote from having offspring.

Question 20

Examples of Pre-zygotic barriers?

Answer 20

1) Habitat Isolation
2) Temporal Isolation
3) Behavioural Isolation
4) Mechanical Isolation
5) Gametic isolation (gamete incompatibility)

Question 21

What is habitat isolation?

Answer 21

Two related species live in different habitats (water & land) and will not encounter one another. No fertilization

Question 22

What is temporal isolation?

Answer 22

Organisms breed at different times during the year. They won’t be able to have kids together. No fertilization.

Question 23

What is behavioural isolation?

Answer 23

Incompatible mating rituals or communication. Typically tied to sexual selection. No fertilization.

Question 24

What is mechanical isolation?

Answer 24

Mating is attempted, but not successful. They are incompatible and yield no fertilization.

Question 25

What is gametic isolation?

Answer 25

Gametes are incompatible with one another, not recognized by one another. No fertilization will occur.

Question 26

What are post-zygotic barriers?

Answer 26

Prevents a zygote from growing up to be a viable, healthy, fertile adult.

Question 27

Examples of Post-zygotic barriers?

Answer 27

Examples include:

• Hybrid inviability
• Hybrid infertility (sterility)
• Hybrid breakdown

Question 28

What is hybrid inviability?

Answer 28

When the organism has a low chance of surviving to adulthood. This could be a developmental problem or have low fitness. They are unlike to be healthy.

Question 29

What is hybrid infertility?

Answer 29

An organism that cannot mate or have children. Very low chance of having children.

Question 30

Example of hybrid infertility?

Answer 30

Mules are animals that have a horse mother and a donkey father. When they have a children it is called a mule and they are very efficient at carrying heavy things over large terrain. The only issue is that they are sterile and unable to reproduce with other mules, horses, and donkeys.

• We are then very comfortable saying that horses and donkeys are separate species.

Question 31

Why are mules infertile?

Answer 31

Horses and donkeys have incompatible chromosome organizations. They were once very closely related species but then both separated and there was evolutionary change on the arrangements of genes and chromosomes.

• This makes a really strange (but viable) hybrid where things do not pair well.
• It causes massive nondisjunction in the gametes of the mules.

Question 32

How do reproductive barriers arise?

Answer 32

Reproductive barriers are the results of evolutionary change in the histories of those species since they experienced speciation.

Question 33

How can reproductive barriers arise accidentally?

Answer 33

Reproductive barriers may rise accidentally as a result of evolution in isolation.

• In other words, a reproductive barrier evolved as a consequence of other evolutionary change.

Question 34

Reproductive barriers example?

Answer 34

Adaptive Evolution:

Changes that were adaptations of those different environments also just happened to be reproductive barriers.

Example: Ideal breeding time shifts for adaptive evolution and now there is a temporal isolation and they will become 2 new species.

Question 35

How can reproductive barriers arise through natural selection?

Answer 35

Reproductive barriers may evolve through natural selection to reduce inter-species mating that lowers reproductive success. “Reinforcement”

• Existing barriers to reproduction, particularly post-zygotic barriers, you may see the evolution of pre-zygotic barriers as well as through natural selection.

Question 36

Allopatric speciation?

Answer 36

Geographic barrier blocks gene flow between populations. It sets up conditions for those populations on either side to evolve in isolation, as there is now no gene flow between them.

Question 37

Sympatric speciation?

Answer 37

New species arise within range of parent population. This occurs without a geographic barrier separating them.

Question 38

Steps of allopatric speciation?

Answer 38

1) Geographic barrier separates populations. A barrier forms, or migrants cross existing barrier, founding new population.

2) Evolutionary change on one or both sides

• Generally thought of as more common
• Their job is to reduce gene flow between populations.

Question 39

Examples of geographic barriers?

Answer 39

• Rivers
• Seas between islands or continents
• Mountain ranges
• Landmasses (barriers for aquatic taxa)

Question 40

Reproductive barriers?

Answer 40

Features of the biology of organisms, things that make them different and move apart.

Question 41

Geographic barriers?

Answer 41

Physical features of the landscape that break up separate populations physically.

Question 42

Isthmus of Panama?

Answer 42

Formed 10-3 million years ago, isolating populations of many marine species.

• Used to be a full waterway. Now we see similarities between the populations of marine life on both sides, but they are different in many ways as well. They are allopatric species.

Question 43

What is evolution after separation?

Answer 43

Species populations become separated by geographic barriers, then evolve separately and tend to resemble one another.

Question 44

Natural selection in allopatric speciation?

Answer 44

Natural selection to different environments (adaptive evolution).

Example: The two sides of Panama might have different environments, meaning that they will adapt separately through natural selection.

Question 45

Genetic drift in allopatric species?

Answer 45

Genetic drift can cause allopatric speciation.

Example: A geological barrier forms and a small group of migrants found a small population in a different habitat. A new group is established and there is no gene flow between the populations.

Question 46

What is the genetic drift an example of coupled with adaptive evolution?

Answer 46

This is the Founder Effect!

• genetic drift and adaptive evolution by natural selection create a new species via the founder effect.

Question 47

What would occur if contact were reestablished between evolved allopatric populations?

Answer 47

1. Complete reproductive barriers evolved: Populations are now two different classic biological species. Depends on if hybrids can be made and their health.
2. Partial reproductive barriers evolved: Formation of hybrids where the species contact. They go to sympatry as there are opportunities to mate.

Question 48

What is fusion?

Answer 48

Hybrids form readily; have high fitness: the incipient species merge into one again.

• High chance of viability and survival
• Expressions of gene flow, they move back to a single species.

Question 49

What is Reinforcement?

Answer 49

Hybrids have low fitness: Natural
selection strengthens barriers -
Hybridization gradually ends and
two good Biological Species are formed.

• They have low fertility
• Natural selection favours strong reproductive barriers

Question 50

What is a Long-Lasting Hybrid Zone?

Answer 50

(e.g. hybrids have variable fitness;
or are uncommon)

• Fitness is variable and are not formed often.

Question 51

Introgression?

Answer 51

Hybrids that breed back with one of the new species can introduce alleles from the other species.

• Passing genetic material between closely related species.
• The incomplete separation of biological species in the real world.

Question 52

Sympatric speciation requires?

Answer 52

It requires a barrier to gene flow within a geographic region.

• Populations become biologically separate species without geographic barriers. Populations that stop experiencing gene flow even though they’re ion the same geographic area.

Question 53

Examples of Sympatric speciation?

Answer 53

• Host switching by specialist herbivores or parasites
• Disruptive selection: favouring evolution of reproductive barriers between individuals with different phenotypes?
• Polyploid speciation, especially in plants

Question 54

Polyploid speciation: allopolyploid example?

Answer 54

A and B can breed but have a different number of chromosomes. When they mate, a new fertile hybrid is formed. It is reproductively isolated from both species A and B.

Question 55

Allopolyploid speciation is?

Answer 55

An example of hybrid speciation.

• common in plants
• exception to a strict “TOL”

Question 56

Speciation and TOL?

Answer 56

Each branching on the tree of life began with a speciation event.

Question 57

What is the biological species concept?

Answer 57

A species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable fertile offspring with members of other such groups.