Evolution Review

Evolution Review Chapters 21, 22, & 23

Ch. 21 Genes within Populations

#2 5 Mechanisms of evolutionary change • 1. Natural selection • traits that improve survival or reproduction will accumulate in the population • adaptive change • 2. Genetic drift • frequency of traits can change in a population due to random chance events • random change • More pronounced in small populations

#2 and #9:Genetic Drift • Chance events changing frequency of traits in a population • not adaptation to environmental conditions • not selection • founder effect • small group splinters off & starts a new colony • it’s random who joins the group • bottleneck • a disaster reduces population to small number & then population recovers & expands again but from a limited gene pool • who survives disaster may be random

albino deer Seneca Army Depot Founder effect • When a new population is started by only a small group of individuals • just by chance some rare alleles may be at high frequency; others may be missing • skew the gene pool of new population • human populations that started from small group of colonists • example:colonization of New World Don’t fenceme in!

Out of Africa Likely migration paths of humans out of Africa Many patterns of human traits reflect this migration

Bottleneck effect • When large population is drastically reduced by a disaster • famine, natural disaster, loss of habitat… • loss of variation by chance event • alleles lost from gene pool • not due to fitness • narrows the gene pool

Cheetahs • All cheetahs share a small number of alleles • less than 1% diversity • as if all cheetahs are identical twins • 2 bottlenecks • 10,000 years ago • Ice Age • last 100 years • poaching & loss of habitat

Conservation issues Peregrine Falcon • Bottlenecking is an important concept in conservation biology of endangered species • loss of alleles from gene pool • reduces variation • reduces adaptability Breeding programs must consciously outcross Golden Lion Tamarin

Mutation Gene Flow Non-random mating Genetic Drift Selection 5 Agents of evolutionary change

#3: Variation & natural selection • Variation is the raw material for natural selection • there have to be differences within population • some individuals must be more fit than others

Ch. 22 Evidence for Evolution

LaMarck (1744-1829) • Organisms adapted to their environments by acquiring traits • change in their life time • Disuseorganisms lost parts because they did not use them — like the missing eyes & digestive system of the tapeworm • Perfection with Use & Needthe constant use of an organ leads that organ to increase in size — like the muscles of a blacksmith or the large ears of a night-flying bat • transmit acquired characteristics to next generation

Then along comes Darwin… Charles Darwin • 1809-1882 • British naturalist • Proposed the idea of evolution by natural selection • Collected clear evidence to support his ideas Galapagos Islands 1831-1836 22 years old!

But Darwin found… a lot of finches Darwin was amazed to find out: All 14 species of birds were finches… But there is only one species of finch on the mainland! Large Ground Finch Small Ground Finch Finch? Sparrow? How didone species of finches becomeso many differentspecies now? Warbler Finch Veg. Tree Finch Warbler? Woodpecker?

Correlation of species to food source Seedeaters Flowereaters Insecteaters Rapid speciation:new species filling new niches,because they inheritedsuccessfuladaptations. Adaptive radiation

Darwin’s finches • Differences in beaks allowed some finches to… • successfully compete • successfully feed • successfully reproduce • pass successful traits onto their offspring

Correlation of species to food source More observations… Whoa,Turtles, too!

Many islands also show distinct local variations in tortoise morphology… …perhaps these are the first steps in the splitting of one speciesinto several?

Moreobservations… Sloth fossils Glyptodont fossils Modern sloth Modern armadillos Why should extinct species & living speciesbe found on thesame continent?

Essence of Darwin’s ideas • Evolution by Means of Natural Selection • variation exists in populations • over-production of offspring • more offspring than the environment can support • competition • for food, mates, nesting sites, escape predators • differential survival • successful traits = adaptations • differential reproduction • adaptations become more common in population

 LaMarckian vs. Darwinian view • LaMarck • in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring • Darwin • giraffes born with longer necks survive better & leave more offspring who inherit their long necks

What are the 4 lines of evidence that support Darwin’s ideas?… Dog Human Macaque Bird Frog Lamprey 8 32 45 125 67 0 10 20 30 40 50 60 70 80 90 100 110 120

1. What are the lines of evidence that support Darwin’s ideas? Fossil record 550 500 450 Equus 400 350 Body size (kg) 300 250 Merychippus 200 Mesohippus 150 Hyracotherium 100 50 Nannippus 60 55 50 45 40 35 30 25 20 15 10 5 0 Millions of years ago

2. What are the lines of evidence that support Darwin’s ideas? Artificial selection Terminal bud Cabbage Brussels sprouts Lateral buds Leaves Flower cluster Kale Cauliflower Stem Flower and stems Kohlrabi Wild mustard Broccoli

3. What are the lines of evidence that support Darwin’s ideas? Anatomical evidence

Homologous structures • Similar structure • Similar development • Different functions • Evidence of close evolutionary relationship • recent common ancestor

Analogous structures Don’t be fooledby their looks! Convergent evolution Those fins & tails & sleek bodies areanalogous structures! Does this mean they have a recent common ancestor? Solving a similar problem with a similar solution

Vestigial organs Why would whaleshave pelvis & leg bonesif they were alwayssea creatures? • These areremnants ofstructures that werefunctional inancestral species

Human/kangaroo 100 Human/ cow Dog/ cow 75 Rabbit/ rodent Human/rodent Llama/ cow Horse/ donkey 50 Nucleotide substitutions Horse/cow Sheep/ goat Pig/ cow 25 Goat/cow 0 0 25 50 75 100 125 Millions of years ago 4. What are the lines of evidence that support Darwin’s ideas? Molecular record • Comparing DNA & protein structure • universal genetic code! • DNA & RNA • compare common genes • cytochrome C (respiration) • hemoglobin (gas exchange) Closely related species have sequences that are more similar than distantly related species • DNA & proteins are a molecular record of evolutionary relationships

Dog Human Macaque Bird Frog Lamprey 8 32 45 125 67 0 10 20 30 40 50 60 70 80 90 100 110 120 The sequence in DNA & proteinsis a molecularrecord of evolutionaryrelationships. Why compare DNA & proteins across species? Comparative hemoglobin structure Why comparethese genes? • compare common genes • cytochrome C (respiration) • hemoglobin (gas exchange) Number of amino acid differences between hemoglobin (146 aa) of vertebrate species and that of humans

Convergent evolution What is thisevidence of? These animals look very similar but doesthat mean they have arecent common ancestor? marsupial mammals placental mammals

Niche Placental Mammals Australian Marsupials Burrower Marsupial mole Mole Anteater Numbat Anteater Nocturnal insectivore Marsupial mouse Mouse Climber Spotted cuscus Lemur Sugar glider Glider Flying squirrel Stalking predator Tasmanian cat Ocelot Chasing predator Wolf Tasmanian “wolf” Parallel/convergent evolution Convergent evolutionof analogous burrowing characteristics

Coevolution • Two or more species reciprocally affect each other’s evolution • predator-prey • disease & host • competitive species • mutualism • pollinators & flowers

#7. Types of Natural Selection • Selection acts on any trait that affects survival or reproduction • predation selection • physiological selection • sexual selection

#8. Effects of Selection • Changes in the average trait of a population DIRECTIONALSELECTION STABILIZINGSELECTION DISRUPTIVESELECTION speciation? giraffe neck horse size human birth weight rock pocket mice

Evolution Review