The Origin of Species

Question 1

What is the source of biological diversity?

Answer 1

The origin of species

Question 2

Natural selection

Answer 2

The gradual adaptation of a population to its environment

Question 3

Mechanism

Answer 3

Microevolution - the change in the gene pool of a population from one generation to the next

Question 4

Speciation

Answer 4

the process by which one species splits into two or more species - explains both diversity and unity of life

Question 5

The biological species concept

Answer 5

Defines a species as a group of populations whose members have the potential to interbreed in nature and produce fertile offspring (offspring that themselves can reproduce). Thus, members of a biological species are united by being reproductively compatible, at least potentially

Question 6

What tends to keep members of different species from physically mating with one another?

Answer 6

Reproductive isolation - prevents genetic exchange (gene flow) and maintains a boundary between species

Question 7

Prezygotic barriers

Answer 7

Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic isolation

Question 8

Postzygotic barriers

Answer 8

Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown

Question 9

Habitat isolation

Answer 9

Lack of opportunities to encounter each other

Question 10

Temporal isolation

Answer 10

Breeding at different times or seasons

Question 11

Behavioral isolation

Answer 11

Different courtship rituals

Question 12

Mechanical isolation

Answer 12

Physical incompatibility of reproductive parts

Question 13

Gametic isolation

Answer 13

Molecular incompatibility of eggs and sperm or pollen and stigma

Question 14

Reduced hybrid viability

Answer 14

Hybrid development or survival impaired by interaction of parental genes

Question 15

Reduced hybrid fertility

Answer 15

Vigorous hybrids that cannot produce viable offspring

Question 16

Hybrid breakdown

Answer 16

Viable and fertile hybrids with feeble or sterile offspring

Question 17

What are some problems with the biological species concept?

Answer 17

• There is no way to determine whether organisms that are now known only through fossils were once able to interbreed
• Reproductive isolation does not apply to prokaryotes or other organisms that reproduce only asexually

Question 18

The morphological species concept

Answer 18

classifies organisms based on observable physical traits and can be applied to asexual organisms and fossils. However, there is some subjectivity in deciding which traits to use. Molecular data sometimes conflicts with morphological data

Question 19

The ecological species concept

Answer 19

Defined a species by its ecological niche and focuses on unique adaptations to particular roles in a biological community. Hinges on ‘ecological niche’ concept - no two species can occupy the same niche

Question 20

In allopatric speciation, what leads to speciation ?

Answer 20

Geographic isolation - a key event in the origin of a new species is the separation of a population from other populations of the same species

Question 21

Allopatric speciation

Answer 21

The initial block to gene flow may come from a geographic barrier that isolates a population. Emergence of mountains or land masses, tectonic plate movements, changes in water level. Individuals colonize a remote area and become geographically isolated from the parent population

Question 22

Can reproductive barriers evolve as populations diverge?

Answer 22

Yes - geographic isolation is just a first step in speciation

Question 23

When does allopatric speciation become even more likely?

Answer 23

If the population sizes are small

Question 24

Peripatric speciation

Answer 24

When both genetic drift and natural selection increase likelihood of divergence

Question 25

Can sympatric speciation take place without geographic isolation?

Answer 25

Yes it can

Question 26

Sympatric speciation

Answer 26

Occurs when a new species arises within the same geographic area as its parent species

Question 27

What three things may reduce gene flow between populations?

Answer 27

Polyploidy, habitat differentiation, or sexual selection

Question 28

Polyploidy

Answer 28

An organisms cells have more than two complete sets of chromosomes
- Auto-polyploidy: within a species (by self-fertilization)
- Allopolyploidy: between two species (by hybridization)

Question 29

Can the origin of most plant species be traced to polyploid speciation?

Answer 29

Yes, 80% of all living plant species are descendants of ancestors that formed by polyploid speciation

Question 30

Sexual selection

Answer 30

A form of natural selection in which individuals with certain traits are more likely to obtain mates - results from differences in how males attract females or how females choose mates

Question 31

Hybrid zones

Answer 31

Regions in which members of different species meet and mate to produce at least some hybrid offspring

Question 32

Reinforcement

Answer 32

When hybrid offspring are less fit than part species, we might expect natural selection to strengthen, or reinforce, reproductive barriers, because members of one species that don’t mate with the other have greater reproductive success
- Increasing reproductive barriers between species when they overlap (that is, where the species are sympatric)

Question 33

Fusion

Answer 33

So much gene flow may occur that the speciation process reverses, causing the two hybridizing species to fuse into one

Question 34

Stability

Answer 34

Many hybrid zones are fairly stable and production of hybrids does allow for some gene flow but the species remain isolated

Question 35

Ring species

Answer 35

Species with a geographic distribution that forms a ring and overlaps at the ends

Question 36

Does speciation occur rapidly or slowly?

Answer 36

It can occur both, rapidly or slowly

Question 37

Punctuated change

Answer 37

Model draws on the fossil record, where species change most as they arise from an ancestral species and then change relatively little for the rest of their existence

Question 38

Gradual change

Answer 38

Species appear to evolve gradually over time