Lecture 11 - Sympatric Speciation Flashcards
What is parapatric speciation?
- Individuals invade new habitat at range edge
- Geography does not limit contact between diverging populations, but they remain connected by gene flow, which is restricted.
Give an example of parapatric speciation.
Greenish warblers.
Five subspecies recognised. Across Europe, differ slightly in morphology and behaviour.
Connected by gene flow.
Species arose in Himalayas and migrated and colonised new habitats.
Two genetic extreme forms are reproductively isolated but are connected by gene flow through the ring.
Describe sympatric speciation.
Populations occupy the same geographic location, with no spatial segregation, and different ‘varieties’ within a species diverge.
Describe polyploid speciation.
Polyploid organisms have 2 sets of chromosomes, and so backcrosses with parental species are not viable due to dysfunctional chromosome complements.
If find another polyploid individual and reproduce, instant reproductive isolation from parental species.
What percentage of vascular plant species ancestry likely included polyploidy?
75%
How did most polyploid species of plants most likely arise?
Through autopolyploidy (multiple chromosome sets derived from a single species)
Why are grasses often polyploid in drier environments?
Hold a higher water content, so more resistant to desiccation.
Describe the work of John Maynard Smith.
Introduced idea of ‘divergence selection’ in 1960s.
Selection operates in different directions to occupy new niches.
Give an example of divergent selection.
In the Periwinkle (Littorina saxatilis):
- Involves ecologically divergent selection over short distances, relative to dispersal
- Two ecotypes in Britain, both found at different heights of the shore: high shore is small and thin shell, mid-shore is large and thick shell.
What is heteropatric speciation?
Micro-allopatric speciation.
Patchy habitats with different ecological conditions in different patches
What method of speciation is it thought that periwinkles evolved by?
Heteropatric speciation
Describe sympatric speciation at the Crater lake.
- Species flocks of cichlid fish in volcanic crater lakes
- 11 endemic cichlids in one, 9 in the other
- Contains unique species not found anywhere else in Africa.
- Each flock radiated from a common ancestor in each lake. Speciation occurred in each lake after single colonisation events.
Describe sympatric speciation on Lorde Howe Island.
- Two endemic palm sister species
- Diverged 2 million years ago
- Substrate living on differs; genetic polymorphism likely arose for a particular type of substrate.
- Lead to differences in timing of flowering, promoting reproductive isolation.
What are magic traits?
A trait, pleiotropic gene, subject to divergent selection and contributing to assortative mating.
What is ecological speciation?
A process by which ecologically-based divergent selection between different environments leads to the creation of reproductive barriers between populations.
