1. Unit 10: Speciation
10.1 Speciation

2. Species
A species is a populations whose members can interbreed and produce fertile offspring
Speciation: The formation of new species through evolution
Example Darwin’s Finches

4. Mechanisms of Speciation: Isolation
Geographic/ habitat isolation
Live in different habitats, rarely see each other
Figure 24.6
A. harrisi
A. leucurus

5. Mechanisms of Speciation: Isolation
Temporal Isolation
Two species breed during different times of the day, different seasons or different years.
These two related frog species exhibit temporal reproductive isolation. (a) Rana aurora breeds earlier in the year than (b) Rana boylii.

6. Mechanisms of Speciation: Isolation
Behavioral Isolation
Special signals attract mates, elaborate behaviors attract mates

7. Mechanisms of Speciation: Isolation
Reproductive Isolation
Is the existence of biological factors that impede members of two species from producing viable, fertile hybrids
Sperm of one species, not able to survive in female of other species

8. Mechanisms of Speciation: Isolation
Mechanical Isolation
They can try, but are anatomically incompatible.

9. Example: Darwin’s Finches
Founders Arrive: finches from South America settle on one of the Galapagos Islands and reproduce.
Geographic Isolation: the new environment was different so natural selection enabled a new species to form. A small sample of this new species moved to inhabit other islands. Because flying over the open water is rare, the finches no longer shared a common gene pool.
Changes in Gene Pools: the differing environment on each island caused natural selection to occur- changing a heritable trait and creating a distinct population characterized by the new phenotype.

10. Example: Darwin’s Finches
Behavioral Isolation: if the birds returned to the original island, they would most likely not interbred. Finches choose mates based on beak size. If one population evolved to have a larger beak, they would not mate with birds with smaller beaks. Therefore, they would not mate with each other, leading to reproductive isolation.
Competition and Continued Evolution: Since the two birds now have specialized food sources, there will be less competition and therefore, reinforce natural selection for certain traits-causing continued evolution of the species.

11. Sexual Selection
Mating choices can change the composition of a population over time. “Survival of the sexiest”
In this case traits DO NOT help an organism survive in a particular environment, but rather help an organism find a mate!
                                                   
                                                   

12. Sexual Selection – 2 methods
Female Choice—females selecting males for their “attractiveness”
Male-Male Competition—males competing with males for females
Note: there are exceptions to this based on species
Who to choose?
She’s mine!

13. Costs of Sexual Selection
Many organisms expend a lot of energy to get mates:
Large showy tails in peacocks
Seals fight for territories
Males build large, showy nests
Some organisms have features to attract mates but are harmful to their survival: (i.e., also attract predators)
Large antlers of moose
Bright coloration in cardinals
Long tail feathers in pheasants

14. Benefits of Sexual Selection
For Males:
Get to pass along their genes!
For Females:
The chance of bearing offspring that will survive and also reproduce.
Parental help
Good territory
**All Benefits Ensure Greater
Survival of the Offspring!!**
A brightly colored male, might, for example, be better and providing food or be less likely to have a disease that would be transmitted to the female or the offspring.
It may be that the female receives no direct benefits from mating with a high quality male, but the male may have high genetic quality so that if a female mates with a high quality male her offspring will inherit the alleles for high quality. A female who mates with a male with high genetic quality should therefore have more surviving offspring.