Ch 23 Mechanisms of Evolution - Which one would not promote change over time?

Natural Selection a major mechanism for evolution Which organisms will be selected, depends on their direct ability to survive & reproduce

What’s the premise of Natural Selection - coined by Charles Darwin… There is a struggle for existence 1. There is a struggle for existence Organisms must compete for limited resources - food, space, a mate. Many more offspring are born each season than can possibly survive 2. Many more offspring are born each season than can possibly survive to maturity (overpopulation) to maturity (overpopulation) 3. Their survival is based on beneficial phenotypes (inherited adaptations) that give them an advantage, increasing their likelihood of survival and production of more viable offspring. 4. Alleles (variations of a trait) tend to increase over time when “selective pressure” favors that phenotype. Over long periods of time, and given a steady input of new variation into 5. Over long periods of time, and given a steady input of new variation into a population, these processes lead to the emergence of new species a population, these processes lead to the emergence of new species

Which premise do these photos demonstrate? What is the selective pressure ? – and what allele or phenotype is favored in each photo?

Survival of The Fittest Rank these apes by fitness level (#1 being the best) Justify your rationale. What is the selective pressure? NameBorisRexHankAbe Age at Death13 years12 years16 years10 years # offspring fathered # offspring surviving into adulthood Size6’2”6’2”5’8”5’8”5’10”5’8”5’8”

Which premise do these photos demonstrate? Advantages/Disadvantages of each and compare. Thornbug Treehopper Emperor Scorpion r/K Selection - Quality vs Quantity - at parental expense

Variation (key to evolution) - comes about in two ways Some fish adapt by evolving antifreeze proteins. 1. Sexual reproduction creates variation causes recombination of alleles into new arrangements in every offspring 2. Mutation creates variation new mutations are constantly appearing (…and it’s not all bad) causes changes DNA sequence (change amino acid sequence? -- protein? -- phenotype? -- fitness??) Genetic shuffling is a source of variation

Reproduction recombines alleles into new arrangements in every offspring Princess Diana, Prince William & Harry Baldwin Brothers Martin Sheen and sons Luke & Owen John Lennon’s sons Cameron & Chimene Diaz Kennedy’s Jonas Brothers Mariska Hargitay & mom Venus & Serena Madonna & daughter Penelope Cruz

What are the beneficial phenotypes? What is the selective pressure that ensures these alleles are kept in the population? Magnificent Frigatebird Predatory Selection - Defensive adaptation Sexual Selection - desire to mate Physiological Selection - desire to survive in their environment Predatory Selection - Cryptic Coloration (camouflage) What “drives” the phenotype?

Natural selection can act in a number of directions In a Directional Selection, the shift in the population is against one extreme variant toward a preferred extreme - the longer neck giraffes are more physically fit and have a better chance of survival and reproduction rate than do the medium or smaller giraffes. What is being selected against? What is being selected for? What’s the selective pressure?

In a Directional Selection, the shift in the population is against one extreme variant toward a preferred phenotype Use one animal from your illustrative examples to create a Title and identify the Independent & Dependent variables on the x & y axes What is being selected against? What is being selected for? What’s the selective pressure?

Natural selection can act in a number of directions In a Stabilizing Selection, the shift in the population is toward the moderate variant - this graphs shows that the two extremes have been reduced in the population, and the medium sized lizards have the best chance at survival & reproduction. What is being selected against? What is being selected for? What’s the selective pressure?

In a Stabilizing Selection, the shift in the population is toward the moderate variant - against/eliminating both extremes Use one animal from your illustrative examples to create a Title and identify the Independent & Dependent variables on the x & y axes What is being selected against? What is being selected for? What’s the selective pressure?

Natural selection can act in a number of directions In a Disruptive Selection, the shift in the population is against the mean/middle selecting for toward both extremes - this graphs shows that the two extremes have been extenuated in the population, those birds with either long beaks or really short beaks have the best chance at survival & reproduction. What is being selected against? What is being selected for? What’s the selective pressure?

In a Disruptive Selection, the shift in the population is selection against the mean, toward both extremes Use one animal from your illustrative examples to create a Title and identify the Independent & Dependent variables on the x & y axes What is being selected against? What is being selected for? What’s the selective pressure?

Changes in populations  Evolution of populations is measuring changes in allele frequency  all the genes & alleles in a population = gene pool  Factors that alter allele frequencies in a population are: 1. natural selection - survival of the fittest 2. genetic drift - evolution is also driven by random, chance events a. founder effect - small group splinters off to start a new colony b. bottleneck effect - some factor (usually a disaster) reduces a population to a small number, then it recovers and expands again. 3. gene flow - immigration and emigration allow for the movement of genes, creating a more diverse gene pool Looking at the following pictures, which factor has created a change in the allele frequencies

b. Gene flow  Population spread over large area  migrations = individuals move from one area to another  sub-populations may have different allele frequencies  Migrations cause genetic mixing across regions = gene flow  new alleles are moving into gene pool  reduce differences between populations

Genetic Drift - as per Founder Effect Founder A Founder B Descendants A Descendants B Some individuals from an original population break away, find a new place and start their own colony - they survive and reproduce Record the allele frequencies for each population. What is this allele frequency?

Genetic Drift - as per Bottleneck Effect When large population is drastically reduced by a disaster  famine, natural disaster, loss of habitat…  loss of variation by chance  alleles lost from gene pool  reduces variation  reduces ability to adapt  puts populations at risk

Any Questions??