Speciation

1. Speciation Speciation • The evolution of new species.

2. Terms • Population-A localized group of individuals belonging to the same species. • Species-A group of populations whose individuals have the potential to interbreed and produce viable offspring.

3. Speciation Physical Barriers limit gene flow Reduced gene flow No gene flow Reproductively Isolated

4. Speciation The population becomes divided by a physical barrier, or just a large distance. This can happen when a population migrates or is dispersed or when the geography changes catastrophically (earthquakes, volcanoes, changes in sea levels) or gradually (erosion, continental drift) Mutations Mutations Barrier prevents gene flow

5. Each fragmented population will be subject to selection pressures that may differ from those experienced by the original population. Different selection pressures will act on different phenotypes changing the frequencies of alleles. Mutations will continue to occur and may be selected for. Mutations Mutations

6. Prezygoticbarriers • Changes in courtship • Differences in breeding seasons • Biochemical changes in ova and sperm • Structural incompatibility • Post zygotic barriers • Sterile hybrids Over time populations accumulate enough change and are so different that they become reproductively isolated. They can no longer interbreed and have become two new distinct species. Species become extinct when they lack the genetic diversity to withstand environmental selection pressures – they fail to adapt

7. Parent population reproductive sub-population Sympatric Speciation • Result of a radical change in the genome that produces a reproductively isolated sub-population within the parent population (rare). • Example: Plant evolution - polyploid A species doubles it’s chromosome to become tetraploid.