Ch24+Speciation+Video+Notes

Speciation Overview

Speciation is the creation of new species.
It can occur in two main ways:
- Allopatric speciation: Occurs when populations are geographically isolated.
- Sympatric speciation: Occurs in overlapping populations.

Gene Flow Interruption: Occurs when a population is geographically isolated.
Independent Evolution: Isolated populations evolve independently via mutation, natural selection, and genetic drift.
Reproductive Isolation: May arise leading to the formation of new species.
Example: Sister species of shrimp separated by the Isthmus of Panama illustrate this with reproductive isolation following the geographical split.
Key Note: Physical separation alone is not a biological barrier; reproductive barriers must be intrinsic to the organisms.

Occurs in geographically overlapping populations.
Can arise if gene flow is reduced by:
- Polyploidy: Presence of extra sets of chromosomes, more common in plants.
- Sexual Selection: Example, color selection in cichlid fish (e.g., P. pundamilia vs. P. nyererei).
- Habitat Differentiation: New ecological niches lead to speciation, as seen with maggot flies on hawthorns versus apples.

Allopatric Speciation:
1. Geographic isolation restricts gene flow.
2. Reproductive isolation may form.
3. New species emerges.
Sympatric Speciation:
1. Reproductive barrier isolates a subset within the same location, leading to new species.

Speciation patterns are observable in the fossil record, as well as morphological and molecular data.
Key questions in speciation studies:
- Duration of speciation events.
- Frequency of speciation events.
- Number of genes involved.
Speciation Rates: Speciation can occur rapidly or slowly; examples include:
- 4,000 years for some cichlids.
- 40 million years for certain beetles.

Investigates how many genes change during speciation:
- A single gene vs. multiple genes.

Macroevolution: Refers to the cumulative effects of many speciation and extinction events.