Unit 10: Speciation 10.1 Speciation

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

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

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.

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

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

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

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.

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. https://www.youtube.com/watch?v=udZUaNKXbJA

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!                                                                                                        

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!

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

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.