Lecture 10 - Allopatric Speciation

Question 1

Name the three concepts that define species.

Answer 1

• The Biological Species Concept
• The phylogenetic Species Concept
• The Morphospecies Concept

Question 2

Who proposed the Biological Species Concept?

Answer 2

Ernst Mayr (1942)

Question 3

Describe the Biological Species Concept.

Answer 3

If populations of organisms do not hybridise, or fail to produce fertile offspring when they do, they are reproductively isolated and are considered separate species.

Question 4

Describe some shortcomings of the Biological Species Concept.

Answer 4

• Many populations cannot be tested for reproductive isolation
• Irrelevant to asexual taxa
• Difficult to apply to many plants where populations are divergent, but hybridisation occurs routinely.

Question 5

Describe the Phylogenetic Species Concept.

Answer 5

Monophyletic groups contain individuals that are all descendants of a single ancestor, and species are defined as the smallest diagnosable monophyletic group.

Question 6

What are some shortcomings of the Phylogenetic Species Concept?

Answer 6

• Phylogenies available for a limited number of species
• Measures of different characters often produce different phylogenies for same set of taxa
• Different species may be diagnosed if they contain small genetic differences, yet these differences may be irrelevant in terms of whether the taxa interbreed
• May double the number of species if applied.

Question 7

Describe the Morphospecies Concept.

Answer 7

Species are defined on the basis of consistent morphological differences.

Question 8

What is a benefit of the Morphospecies Concept?

Answer 8

It is universal - people can measure and compare morphology.

Question 9

What are some shortcomings of the Morphospecies Concept?

Answer 9

• Some species show polymorphic morphology
• Could be subjective and difficult to apply consistently
• Difficult to apply to cryptic species.

Question 10

What method is powerful at identification of cryptic species?

Answer 10

DNA barcoding.

Question 11

Describe the species identification of the Red Wolf.

Answer 11

• Underwent large population decline by 1970s.
• 14 were captured for captive breeding and reintroduction.
• Skulls collected before 1930 had distinctive cranial characteristics, suggesting red wolves were a morphospecies.
• After 1930, resembled skulls of coyotes; hybridisation with red wolves unable to find suitable mates?

Question 12

What is allopatric speciation?

Answer 12

Where populations are prevented from exchanging genes by a geographic isolation.

Question 13

Give the two forms of allopatric speciation.

Answer 13

• Vicariant speciation

- Peripatric speciation

Question 14

Describe vicariant speciation.

Answer 14

Populations are divided by the emergence of an extrinsic barrier.

Question 15

What kind of populations are normally affected by vicariant speciation?

Answer 15

Large, widespread populations.

Question 16

Give an example of vicariant speciation.

Answer 16

In snapping shrimp.
Land bridge appeared in Isthmus of Panama, dividing the oceans.
Identification of seven ‘morphospecies’ with similar morphologies either side of Central America.

Question 17

Describe peripatric speciation.

Answer 17

A ‘colony’ diverges from a widespread ‘parent’ population, and acquires reproductive isolation.
Genetic drift may be important in the evolution of a new species on the smaller colony.

Question 18

Give an example of peripatric speciation.

Answer 18

In Marine lakes of Palau, lakes formed in chronological series as sea levels rose.
Ancestral jellyfish disperses to new lakes and populations become morphologically, behaviourally and genetically more divergent with lake age.

Question 19

What is some good evidence for parallel speciation?

Answer 19

Three-Spined sticklebacks; different forms evolved in several lakes via ‘double invasion’.

Question 20

What is assortative mating?

Answer 20

Individuals with similar genotypes and/or phenotypes mate with one another more frequently.

Question 21

What is sexual selection?

Answer 21

Members of one biological sex choose mates of the other sex with whom to mate.

Question 22

What is some evidence for sexual selection and assertive mating promoting speciation?

Answer 22

Species diversity is highest in clades of bird species where the sexes are dimorphic, rather than in related monomorphic clades.
Therefore, sexual selection increases speciation rate.

Question 23

What happens in allopatric speciation if geographic isolation breaks down?

Answer 23

Populations come back into Secondary Contact, and hybridisation may be possible.

Question 24

What are some pre zygotic barriers to gene flow?

Answer 24

• Behavioural barriers
• Mechanical barriers
• Gametic incompatibility

Question 25

What are some post zygotic barriers to gene flow?

Answer 25

• Zygotic mortality
• Hybrid inviability
• Hybrid sterility

Question 26

What is reproductive character displacement?

Answer 26

Differences in traits involved with mate choice/mating compatibility among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur, but are minimised or lost where the species’ distributions do not overlap.

Question 27

Give an example of reproductive character placement.

Answer 27

In stag beetles:

• in sympatry, they are strikingly different in colour patterning. Also vary in body and genital length.
• In allopatry, they are very similar in colour, and body and genital length do not vary.