1. Speciation

2. Microevolution
Small (hence “micro”) shifts in allele frequencies in populations and species
Causes changes in phenotypes in populations and species
Genetic drift, directional, disruptive, stabilizing, sexual selection
Evolution at the species level

3. Species
A group of organisms that can interbreed and produce fertile offspring
Some species can interbreed; e.g., bacteria, dogs, wolves, coyotes, plants (tangelo= tangerine+pomelo)
Sometimes it is necessary to rely on DNA evidence to distinguish between species, different ecological niches of the organism

4. Tangelo

5. Speciation
Formation of a new species

6. Reproductive Isolating Mechanisms
Any behavioural, structural, or biochemical traits that prevent individuals of different species from reproducing successfully

7. Prezygotic Mechanisms
Prevent mating, fertilization and zygote formation
Ecological isolation – occupy different habitats
Temporal isolation – breed at different times of year
Behavioural isolation – different mating rituals and signals
All methods that prevent mating
Behavioural: Male frogs of different species have unique calls that attract only females of their own species

8. Prezygotic Mechanisms
4. Mechanical Isolation: Difference in physical
features that make mating impossible.
Different/Incompatible genitalia
5. Gametic isolation – gametes not able to recognise each other
Methods that prevent fertilization
The genitalia of male and female Damselflies of different species differ

9. Postzygotic Mechanisms
Mechanisms that prevent fertilized egg from growing into a fertile adult

10. Postzygotic Mechanisms
Zygotic mortality – zygote dies
Hybrid inviability – the hybrid does not live long, either as an embryo or new born
Hybrid infertility – the hybrid is unable to produce offspring

11. Modes of Speciation
Isolated populations that undergo mutations, followed by selection, will eventually not be able to share their alleles with other populations that were once related
Results from geographical isolation, commonly

12. Allopatric Speciation
Evolution of populations into separate species because of geographical isolation; e.g., canyon, mountains

14. The scene: a population of wild fruit flies minding its own business on several bunches of rotting bananas, cheerfully laying their eggs in the mushy fruit...
Disaster strikes: A hurricane washes the bananas and the immature fruit flies they contain out to sea. The banana bunch eventually washes up on an island off the coast of the mainland. The fruit flies mature and emerge from their slimy nursery onto the lonely island. The two portions of the population, mainland and island, are now too far apart for gene flow to unite them. At this point, speciation has not occurred — any fruit flies that got back to the mainland could mate and produce healthy offspring with the mainland flies.
The populations diverge: Ecological conditions are slightly different on the island, and the island population evolves under different selective pressures and experiences different random events than the mainland population does. Morphology, food preferences, and courtship displays change over the course of many generations of natural selection.
So we meet again: When another storm reintroduces the island flies to the mainland, they will not readily mate with the mainland flies since they've evolved different courtship behaviors. The few that do mate with the mainland flies, produce inviable eggs because of other genetic differences between the two populations. The lineage has split now that genes cannot flow between the populations.

15. Sympatric Speciation
Evolution of populations within larger populations in the same geographical area
Occupy different niches and become quite distinct over time due to selection

17. Sympatric Speciation
Polyploidy – more than the regular 2 copies of each chromosome
Humans are diploid as are many other species
Polyploidy can result from a mutation.
Many plants (30% to 70%) and some frogs and fish are polyploid
Polyploid gametes are 2n  homologous pairs  diploid hybrid
Polyploids can produce fertile offspring when mated with other polyploids
Hybrid is new species that will not produce fertile offspring if crossed with the parent species.

19. Human Influence Destruction of habitat
Separation of habitats – dams, roads, etc.

20. Your Task
Read pp #1-5