Chapters 15-17 Evolution

Science Definitions

Theory A well-substantiated explanation of some aspect of the natural world that typically incorporates many confirmed observations, laws and successfully verified hypotheses. Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html

Evolution Book definition = Gradual accumulation of adaptations over time. In genetic terms, the change in the frequency of alleles in populations from generation to generation. (change over time) Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html

Adaptation Any heritable characteristic (determined from alleles) of an organism that improves its ability to survive and reproduce in its environment. Note: not all characteristics are adaptive Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html

Adaptations http://animals.nationalgeographic.com/

Fitness The success of an individual in surviving and reproducing, measured by that individual’s genetic contribution to subsequent generations. Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html

Natural Selection Charles Darwin’s Theory Mechanism for change in populations. Occurs when organisms with certain traits survive, reproduce and pass their variations to the next generation. “Survival of the Fittest”

Natural Selection 1. Variations exist in a population

Sweet! I’m better at surviving because I blend into my surroundings! Natural Selection 2. Some variations improve the ability to survive and reproduce in the particular environment Sweet! I’m better at surviving because I blend into my surroundings! Dang!

I have more fitness than you! Natural Selection 3. The individuals with the adaptive traits are more likely to pass on their genes to future generations Dang! I have more fitness than you!

Natural Selection 4. Over time, the frequency of adaptive alleles increases = evolution.

The Four Tenants of Natural Selection… OVERPRODUCTION: Organisms produce more offspring than their environment can support. HERITABLE VARIATION: Offspring vary in their appearance and function; some of these variations are heritable. COMPETITION: Offspring must compete for survival, food and reproduction. SURVIVAL OF THE FITTEST: Offspring who have the highest fitness for their environment will live longer and/or leave more offspring than those less suited for the environment.

Can we see natural selection in one generation? This process occurs very slowly, over many generations Natural selection can only be observed as changes in the characteristics or behaviors in populations over time.

Natural Selection… Caterpillars… what is the benefit of looking like bird poop?

Overproduction & Heritable Variation in butterflies… How many offspring do butterflies produce? 1000+ offspring … not that many survive What kind of variation could we see in larva (caterpillars)? Different color patterns Different sizes Diet Is this variation in color patterns heritable? Genes control color patterns in all organisms… Offspring from a butterfly (caterpillar) that was green as a larva? Offspring from a butterfly (caterpillar) that was brown and white as a larva?

Competition & Survival of the Fittest… Caterpillars have competition for food, survival & reproduction. Who will survive the longest? Best camouflage = less likely to be seen by predators = longer survival = more reproduction If those that look like bird poop survive longer, what will the population start to look like over many generations? Like bird poop! NATURAL SELECTION – the natural selection of characteristics that allow an animal to survive and reproduce (sometimes because of their ability to blend in with their environment)– makes them more fit.

Other examples of selection for survival…

Natural Selection… Cheetahs… why can they run so fast?

Overproduction & Heritable Variation in cheetahs… How many offspring do cheetahs produce? 5-6 offspring per year … not that many survive What kind of variation could we see in cheetahs? Size of the heart Length of the legs Color patterns + many others Is this variation in length of legs heritable? Genes control color length of limbs in all organisms… Offspring from a cheetah with long legs? Offspring from a cheetah with short legs?

Competition & Survival of the Fittest… Cheetahs have competition for food, survival & reproduction. Who will survive the longest? Those that can run fast enough to catch prey to survive = longer survival = more reproduction. If those that look run faster eat more, what will the population start to look like over many generations? Fast runners! NATURAL SELECTION – the natural selection of characteristics that allow an animal to get more food within their environment – makes them more fit.

Sexual Selection… The male peacock… why waste so much energy producing feathers?

Overproduction & Heritable Variation in peacocks How many offspring do they produce? 6-8 per year are hatched… not that many survive What kind of variation could we see in male peacocks? Different color patterns Different feather sizes Size of bird Is this variation in feather size heritable? Genes control how large feathers will get… Offspring from a peacock with large feathers? Offspring from a peacock with short feathers?

Competition & Survival of the Fittest… Peacocks have competition for food, survival & reproduction. Who will reproduce the most? Largest feathers = more reproduction If those with large feathers reproduce more, what will the population start to look like over many generations? Larger feathers, on average. SEXUAL SELECTION – the natural selection of secondary sex characterizes in males is WORTH the energy they spend because it increases levels of reproduction – makes them more fit.

Other interesting secondary sex characteristics….

Natural Selection in the last few years…

Antibiotic Resistance

AZT-Resistant HIV (AIDS virus)

AZT-Resistant HIV (AIDS virus) Resistance to AZT has evolved in all patients taking the drug (usually in ~6 months)! How does HIV evolve so rapidly? 1. High mutation rate • HIV’s mutation rate is 106 higher than ours! 2. Short generation time • 1 year ≅ 300 viral generations. 10 years of viral ≅ 2-3 x 106 years of human evolution!

Bt-resistant Cotton Bollworm

Natural Selection Last week we did a lab demonstrating natural selection… you just didn’t know about it. ?

Directional Selection Stabilizing Selection Assignment #1 Complete the following chart using pages 398 & 399 Definition Example Picture Directional Selection Stabilizing Selection Disruptive Selection

Assignment #2 Complete the following chart using pages 404 & 405 Definition Example Picture Behavioral Isolation Geographic Isolation Temporal Isolation

Speciation The first steps of speciation have been produced in several laboratory experiments involving “geographic” isolation. For example, Diane Dodd took fruit flies from a single population and divided them into separate populations living in different cages to simulate geographic isolation. Half of the populations lived on maltose-based food, and the other populations lived on starch-based foods. After many generations, the flies were tested to see which flies they preferred to mate with. Dodd found that some reproductive isolation had occurred as a result of the geographic isolation and selection in the different environments: “maltose flies” preferred other “maltose flies,” and “starch flies” preferred other “starch flies.”

Speciation One species splits into two due to isolation (geographic, reproductive, etc…) Also known as Divergent Evolution… results in homologous structures between groups

Speciation Hurricane http://evolution.berkeley.edu

Speciation 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. http://evolution.berkeley.edu

Speciation 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. http://evolution.berkeley.edu

Speciation http://evolution.berkeley.edu

Some Evidence of Evolution Geographic Locations Anatomical Similarities Developmental Similarities Molecular (biochemical) Similarities

Some Evidence of Evolution Geographic Locations

Some Evidence of Evolution Anatomical Similarities Homologous Structures = structural features with a common evolutionary origin. Similar in arrangement, function or both.

Some Evidence of Evolution Anatomical Similarities Homologous Structures

Some Evidence of Evolution Anatomical Similarities Homologous Structures http://www.ucmp.berkeley.edu/

Analogous Structure = A structural or functional similarity of a body feature, but not related. Example: Insect & bird wings are similar in function, but not structure

Some Evidence of Evolution Anatomical Similarities Vestigial Structures = a body structure that has no function in a present-day organism but was probably useful to an ancestor.

Some Evidence of Evolution Anatomical Similarities Vestigial Structures

Some Evidence of Evolution Developmental Similarities Comparative embryology Early developmental stages are compared. Related embryos look similar. Page 410 (bird, deer, human) Look for tails and gill slits.

Some Evidence of Evolution Developmental Similarities Comparative embryology

Some Evidence of Evolution Molecular (biochemical) Similarities

Some Evidence of Evolution Molecular (biochemical) Similarities

Some Evidence of Evolution Anatomical Similarities Fossils Evidence of an organism that lived long ago. Most fossils are found in Sedimentary rock. 6 types (page 378) http://www.earthhistory.org.uk/wp-content/crayfish.jpg

1. Trace Fossils https://courseware.e-education.psu.edu/courses/earth105new/graphics/L02_fossil_hpl922.jpg

2. Casts http://www.activityvillage.co.uk/cast-fossils.jpg

3. Imprints http://www.hopefossils.co.uk/Fossil%20photos/Trilobite%20under%20x10%20magnification%20-%20Placoparia%20cambriensis.JPG

4.Amber-Preserved & Frozen http://dsc.discovery.com/news/2007/10/08/gallery/amber_zoom.jpg

5. Petrified http://www.legendsofamerica.com/photos-arizona/PetrifiedWood.jpg

6. Molds http://www.ammonoid.com/mcE-m.jpg

Geologic Time Scale – Page 421 Notice the short amount of time that humans have been a part of Earth’s history. http://www.life.illinois.edu/mcb/419/images/GeoTimeSpiral.jpg

Phylogeny Figure 1: A diagram of Mimi's immediate family. The passage of genes from parents to offspring is indicated by the green lines.

Figure 2: The genetic relationships for the last three generations of beetles under Mimi's log.

Figure 3: Genetic relationships for a segment of Mimi's beetle population over a number of generations. The last three generations of beetles under Mimi's log are shown in the blue frame.

Figure 4: Genetic relationships between two closely related species, Bembidion levettei and Bembidion zephyrum. Recent generations of beetles in Mimi's species are indicated with the blue frame. The arrow points to the common ancestor of the two beetle species.

Figure 5: A phylogenetic tree of beach beetles Figure 5: A phylogenetic tree of beach beetles. Some branches have gone extinct in the past, while others represent species living today.

Figure 6: Genetic connections flowing along the branches of the Tree of Life.

??? Figure 7: The Tree of Life that we’ll be using for the rest of the semester.