Beaks of Darwin’s Finches Darwin collected 31 specimens from 3 islands in the Galápagos Islands – Darwin not an expert on birds – Took them back to England for identification – Told his collection was a closely related group of distinct species – All were similar except for beak characteristics – In all, 14 species now recognized 1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Woodpecker finch (Cactospiza pallida) Large ground finch (Geospiza magnirostris) Cactus finch (Geospiza scandens) Warbler finch (Certhidea olivacea)Vegetarian tree finch (Platyspiza crassirostris) 2

Finches eat a diversity of foods Darwin hypothesized that different beak shapes were related to food gathering – Darwin wrote “… one might really fancy that … one species has been taken and modified for different ends.” 3

Modern research has verified Darwin’s selection hypothesis 3 conditions of natural selection – Phenotypic variation must exist in the population – This variation must lead to differences among individuals in lifetime reproductive success – Phenotypic variation among individuals must be genetically transmissible to the next generation. 4

Industrial melanism Phenomenon in which darker individuals come to predominate over lighter ones – Other moths in other industrialized areas showed same trend to darken Pollution control resulted in bark color being lighter again Light-colored peppered moths now are dominant in the population 5

Artificial Selection Change initiated by humans Operates by favoring individuals with certain phenotypic traits, allowing them to reproduce and pass their genes on to the next generation This directional selection should result in evolutionary change 6

Can selection produce major evolutionary changes? 7 Most scientists think that natural selection is the process responsible for the evolutionary changes documented in the fossil record Some critics of evolution accept that selection can lead to changes within a species, but not the substantial changes documented in the fossil record This argument does not fully appreciate the extent of change produced by artificial selection – Dog breeds would be species if found as fossils

Domestication – Human-imposed selection has produced a variety of cats, dogs, pigeons, and others – Breeds may have been developed for specific purposes Dachshunds for badger pursuit 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Greyhound Dachshund Chihuahua Wolf Mastiff

Evolutionary transitions Given the low likelihood of fossil preservation and recovery, it is not surprising that there are gaps in the fossil record Intermediate forms have been found Oldest known bird fossil is the Archaeopteryx – Clearly intermediate between bird and dinosaur – Possesses some ancestral traits and some traits of present day birds 9

Archaeopteryx 10

Anatomical Evidence for Evolution Homologous structures – Structures with different appearances and functions that all derived from the same body part in a common ancestor – The bones in the forelimb of mammals are homologous structures – Different functions, same ancestor structure 11

12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PorpoiseHorse BatCatHuman Humerus Radius Ulna Carpals Metacarpals Phalanges

Early embryonic development – Strongest anatomical evidence supporting evolution comes from comparisons of how organisms develop – Embryos of different types of vertebrates, for example, often are similar early on, but become more different as they develop – Early vertebrate embryos possess pharyngeal pouches that develop into In humans: glands and ducts In fish: gill slits 13

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Imperfections – some organisms do not appear perfectly adapted Workable but imperfect solutions Most animals with long necks have many vertebrae for flexibility – Geese: 25 – Plesiosaurs: 76 – Mammals: 7 The giraffe has 7 vertebrae, very large in size, to make up for the length of the neck 15

Convergent evolution Similar forms having evolved in different, isolated areas because of similar selective pressures in similar environments Marsupial and placental mammals – Only marsupials found in Australia – Australian marsupials resemble placental mammals on other continents 16

17 NicheBurrowerAnteater Nocturnal Insectivore ClimberGlider Stalking Predator Chasing Predator Australian Marsupials Placental Mammals Mole Marsupial mole Numbat Marsupial mouse Spotted cuscus Grasshopper mouse Ring-tailed lemur Flying squirrel Flying phalangerTasmanian quoll Thylacine Wolf Ocelot Lesser anteater Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Convergence among fast-moving marine predators Hydrodynamics of moving through water require a streamlined body shape to minimize friction Sharks, tuna, icthyosaurs, and dolphins 18

The Biological Species Concept Ernst Mayr defined species as … “… groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups” Species composed of populations whose members mate with each other and produce fertile offspring Reproductive isolation – do not mate with each other or do not produce fertile offspring 19

Gene exhange The biological species concept focuses on the ability to exchange genes – Prezygotic isolating mechanisms Mechanisms that prevent formation of a zygote – Postzygotic isolating mechanisms Mechanisms that prevent development into an adult 20

Reproductive isolating mechanisms – Prezygotic isolating mechanisms Ecological isolation Behavioral isolation Temporal isolation Mechanical isolation Prevention of gamete fusion – Postzygotic isolating mechanisms Hybrid inviability or infertility 21

Postzygotic isolating mechanisms – Leopard frogs form a group of related species Many hybrids cannot be produced even in the laboratory – Hybrids that do survive may be weaker – Hybrids may be sterile – mules Abnormal sex organs Failure to form gametes 22

Ecological species concept – Distinctions among species are maintained by natural selection – Stabilizing selection maintains the species’ adaptations – Hybrids are quickly eliminated from gene pool 23

Adaptive radiations Closely related species that have recently evolved from a common ancestor by adapting to different parts of the environment Occurs – In an environment with few other species and many resources Hawaiian and Galápagos Islands – Catastrophic event leading to extinction of other species 24

Key innovation – New trait evolves within a species allowing it to use resources that were previously inaccessible Lungs in fish Wings in birds – Requires both speciation and adaptation to different habitats Island archipelago example An ancestral species flies from main land to colonize one island. 2. The ancestral species spreads to different islands. 3. Populations on different islands evolve to become different species. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

26 4. Species evolve different adaptations in allopatry. 4. Colonization of islands. 5. Colonization of islands.5. Species evolve different adap- tations to minimize competition with other species (character displacement). a.b. or Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Genetic Drift Changes in gene pool of populations due to random chance

Genetic Drift

Genetic Drift Image Credit: UC Museum of Paleontology's Understanding Evolution

Genetic Drift Genetic drift has a bigger effect on small populations.

Bottleneck Effect Changes in gene pool of populations due to some event  drastically reduces population

Bottleneck Effect Survival is random Whether an organism survives does not depend on any characteristic (allele)

Example of Bottleneck Effect Population of plants on a mountain side An avalanche wipes out all but a patch of plants behind the shelter of a large outcrop.

Example of Bottleneck Effect Plants behind the outcrop survived only because they were out of the path of the avalanche. There was nothing about the plants’ genes that influenced survival.

Example of Bottleneck Effect Surviving population has an allele frequency different from the original population.

Bottleneck Effect

Bottleneck Effect: Cheetahs 10,000 years ago, cheetah populations worldwide crashed Due to climate change Photo Credit: Courtesy of Smithsonian National nationalzoo.si.edu

Cheetahs Only cheetahs in Africa & Eurasia survived Location, not genes  Survival Photo Credit: Kevin Walsh, 2006, Wikimedia Commons

Cheetahs Cheetahs today: Genetically identical Photo Credit: Lukas Kaffer, 2007, courtesy of Wikimedia Commons

Bottleneck Effect: Northern Elephant Seals Once numerous in the northern Pacific. 1800s: Hunted extensively for blubber Photo Credit: Michael Baird of bairdphotos.com, courtesy of Wikimedia Commons

Northern Elephant Seals Only animals in a Mexican colony survived Photo Credit: Michael Baird of bairdphotos.com, courtesy of Wikimedia Commons

Northern Elephant Seals Today: >100,000 individuals Very little genetic diversity Photo Credit: Mila Zinkova, 2008, courtesy of Wikimedia Commons

Founder Effect New population established by very small number of individuals (“founders”) By chance, founder group has a different allele mix than original population

Example of Founder Effect 200 German immigrants founded the Old Order Amish of Pennsylvania Photo credit: : Matthew Trump, 2004, Wikimedia Commons

Old Order Amish One couple brought allele polydactyly  Six fingers and toes Photo credit: G. Baujat and M LeMerrer, 2007, Wikimedia Commons

Old Order Amish Inbreeding has  frequency of polydactyly Click on this link: 06/3/l_063_03.html 06/3/l_063_03.html Photo credit: gadjoboy, 2006, Wikimedia Commons