Unit 9: Evolution 9.4 How Evolution Happens

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

How Evolution Happens Mutation Isolation Sexual Selection

Mutations Changes in the DNA that may change a trait in an organism. Some mutations go unnoticed…not all changes in DNA impact survival. Some mutations are negative…and can be fatal. Some mutations are beneficial…and may lead to changes in a population over time through natural selection. https://www.youtube.com/watch?v=1fN7rOwDyMQ

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

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.

Isolation Behavioral Isolation Special signals attract mates, elaborate behaviors attract mates

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

Isolation Mechanical Isolation They can try, but are anatomically incompatible.

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.

3 Types of Natural Selection Natural selection can affect the relative fitness of phenotypes producing 3 different types: Directional Selection Stabilizing Selection Disruptive Selection

Directional Selection Directional Selection: When individuals at one end of the curve have higher fitness. Usually happens when the environment changes or a species moves to a new location. Example: Size and shape of finch beaks based on the availability of certain seeds.

Stabilizing Selection Stabilizing Selection: When individuals near the center of the curve have higher fitness than individuals at either end Example: Birth weight in human babies

Disruptive Selection Disruptive Selection: When individuals at the outer ends of the curve have higher fitness than individuals near the middle of the curve Example: Birds with small and large beak sizes with nothing in the middle

Patterns of Evolution Convergent Evolution: the process whereby organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches Example: similar nature of flight/wings of insects, birds, pterosaurs, and bats Results in analogous structures

Patterns of Evolution Divergent Evolution: the process whereby organisms that are closely related species split into two or more different species. Example: Darwin’s finches- 15 species diverged from a single species of finch that arrived on the Galapagos islands Results in homologous structures