Speciation Models

Question 1

What is speciation?

Answer 1

Speciation is the process by which new species are formed, often described as the origin and spread of reproductive isolating barriers.

Question 2

What are the two geographic models of speciation?

Answer 2

Allopatric speciation involves a geographic barrier, while sympatric speciation occurs without geographic separation.

Question 3

Why is speciation considered a continuous process?

Answer 3

Because any population has the potential to diverge into separate species, but it does not necessarily mean divergence will occur.

Question 4

What is allopatric speciation?

Answer 4

Speciation that occurs due to the presence of geographic barriers that prevent gene flow.

Question 5

What are the two main modes of geographic isolation in allopatric speciation?

Answer 5

Dispersal, where a portion of a population colonizes a new area, and vicariance, where a geographic barrier splits a population.

Question 6

What happens as divergence proceeds in allopatry?

Answer 6

Mutation, drift, selection, and gene flow occur independently in the isolated populations, leading to differentiation over time.

Question 7

What is secondary contact?

Answer 7

When previously separated populations come back into contact, potentially testing their reproductive isolation.

Question 8

What is an example of vicariance leading to speciation?

Answer 8

The formation of the Isthmus of Panama, which separated marine populations on the Atlantic and Pacific sides, leading to sister species pairs.

Question 9

How does dispersal lead to speciation in the Hawaiian Islands?

Answer 9

Isolated islands facilitated the dispersal of species, leading to divergence through drift and selection, with many species becoming endemic.

Question 10

How does reproductive isolation accumulate in allopatry?

Answer 10

Studies, such as those on Drosophila, show that pre-zygotic isolation becomes stronger with increased genetic distance and time since divergence

Question 11

What are the three outcomes of secondary contact?

Answer 11

Species merge, form a hybrid zone, or undergo reinforcement to strengthen reproductive isolation.

Question 12

What is an example of species merger?

Answer 12

Freshwater sticklebacks in British Columbia, where habitat changes led to the collapse of the limnetic form, merging populations.

Question 13

What is a hybrid zone?

Answer 13

A region where gene flow occurs between previously isolated populations, resulting in hybrids.

Question 14

What is reinforcement in speciation?

Answer 14

he strengthening of pre-zygotic barriers to prevent the production of less fit hybrids, such as in Drosophila where females in sympatric regions show stronger mate discrimination.

Question 15

What is sympatric speciation?

Answer 15

The formation of new species within the same geographic area without physical barriers.

Question 16

What conditions favor sympatric speciation?

Answer 16

Strong selection, ecological divergence, and pre-zygotic isolation, such as shifts in flowering times in Howea palms.

Question 17

What are magic traits?

Answer 17

Traits subject to divergent selection that also influence non-random mating, facilitating sympatric speciation.

Question 18

What is hybrid speciation?

Answer 18

The formation of a stable and reproductively isolated hybrid species, which can occur via homoploid or polyploid speciation.

Question 19

What helps hybrid species establish?

Answer 19

Ecological separation from parent species and rapid, strong genetic isolation, such as sex-linked incompatibilities in Italian sparrows.

Question 20

How does hybrid speciation differ from hybrid zones?

Answer 20

Hybrid species are genetically stable and isolated from parents, while hybrids in zones often result from ongoing gene flow and are less fit.

Question 21

How does selection drive speciation?

Answer 21

Adaptation and selection play key roles in forming reproductive barriers, especially when gene flow occurs during divergence or after secondary contact.

Question 22

Why is gene flow considered an obstacle to speciation?

Answer 22

Gene flow and recombination homogenize genetic differences, making divergence harder to sustain.

Question 23

What is an example of ecological selection driving speciation?

Answer 23

Timema walking sticks, which are adapted to different host plants, experience ecological isolation that prevents gene flow.

Question 24

What is a supergene, and how does it relate to speciation?

Answer 24

A supergene is a cluster of linked genes that influence traits critical for reproductive isolation, as seen in Howea palms.