Lecture 10 - Allopatric Speciation Flashcards
Name the three concepts that define species.
- The Biological Species Concept
- The phylogenetic Species Concept
- The Morphospecies Concept
Who proposed the Biological Species Concept?
Ernst Mayr (1942)
Describe the Biological Species Concept.
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.
Describe some shortcomings of the Biological Species Concept.
- 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.
Describe the Phylogenetic Species Concept.
Monophyletic groups contain individuals that are all descendants of a single ancestor, and species are defined as the smallest diagnosable monophyletic group.
What are some shortcomings of the Phylogenetic Species Concept?
- 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.
Describe the Morphospecies Concept.
Species are defined on the basis of consistent morphological differences.
What is a benefit of the Morphospecies Concept?
It is universal - people can measure and compare morphology.
What are some shortcomings of the Morphospecies Concept?
- Some species show polymorphic morphology
- Could be subjective and difficult to apply consistently
- Difficult to apply to cryptic species.
What method is powerful at identification of cryptic species?
DNA barcoding.
Describe the species identification of the Red Wolf.
- 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?
What is allopatric speciation?
Where populations are prevented from exchanging genes by a geographic isolation.
Give the two forms of allopatric speciation.
- Vicariant speciation
- Peripatric speciation
Describe vicariant speciation.
Populations are divided by the emergence of an extrinsic barrier.
What kind of populations are normally affected by vicariant speciation?
Large, widespread populations.
Give an example of vicariant speciation.
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.
Describe peripatric speciation.
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.
Give an example of peripatric speciation.
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.
What is some good evidence for parallel speciation?
Three-Spined sticklebacks; different forms evolved in several lakes via ‘double invasion’.
What is assortative mating?
Individuals with similar genotypes and/or phenotypes mate with one another more frequently.
What is sexual selection?
Members of one biological sex choose mates of the other sex with whom to mate.
What is some evidence for sexual selection and assertive mating promoting speciation?
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.
What happens in allopatric speciation if geographic isolation breaks down?
Populations come back into Secondary Contact, and hybridisation may be possible.
What are some pre zygotic barriers to gene flow?
- Behavioural barriers
- Mechanical barriers
- Gametic incompatibility
What are some post zygotic barriers to gene flow?
- Zygotic mortality
- Hybrid inviability
- Hybrid sterility
What is reproductive character displacement?
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.
Give an example of reproductive character placement.
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.
