Genetic variation and Evolution Chapter 20 Why are

Genetic variation and Evolution Chapter 20 Why are organisms well adapted to their habitats? Creationist explanation (see section 21. 7) 20. 2 -- should know H-W equation and why it’s important -- we may come back to this Is a religious view Divine role 20. 4 – understand the meaning of fitness, but we’ll not cover the mathematical aspects 20. 5 – skip “intelligent design” not scientifically testable Scientific explanation 20. 6 – read on your own 20. 8 – read on your own “evolution from common ancestor” ‘Natural Selection” -- is testable Genetic Variation & Evolution 1

Darwin was not first to describe evolution George Cuvier (1790) – Fossils & ‘Catastrophism’ Jean Lamarck (1809) -- Environmental influence Lamarck’s theory of “Inheritance of Acquired Traits” Genetic Variation & Evolution 2

Modern explanations of why traits change over time (20. 3) Why do the traits of a species change over time 5 Agents (mechanisms) of change: 1. Genetic Mutation – random changes to DNA code -- is the ultimate source of all new traits -- creates variation within a piopulation -- ‘raw material’ of all evolutionary mechanisms 2. Natural selection – mechanism proposed by Darwin -- environment selects certain traits Genetic Variation & Evolution 3

Agents of change, con’t Gene Flow Other agents of change 3. Gene flow -- movement of individuals between populations 4. Nonrandom mating -- organisms prefer to mate with certain individuals 5. Genetic drift Animation -- random variation in the distribution of traits from one generation to the next. Founder effect Bottleneck effect Extreme examples Founder effect – population isolation bottleneck effect – population catastrophe -- gene pool reduction Genetic Variation & Evolution 4

What are the fundamental premises of Darwin’s theory of “Natural Selection”? Read Section about Evolution in Chapter 1 “On the Origin of Species by Means of Natural Selection” “Evolution” (a process) does not equal “Natural Selection” (a process) Natural selection occurs when: 1) There exists genetically based variation (inheritable) in the traits of a species. 2) Organisms produce more offspring than can survive. 3) The environment selects for those organisms with the best adapted traits. -- i. e. , interactions with other organisms & habitat 4) Organisms best adapted to the environment will reproduce most successfully. Genetic Variation & Evolution 5

There is variation in all traits of all species What is nature of genetic variation? = a range of forms Genetic variation in Asiatic lady beetle Why? Genetic mutation DNA Polymorphisms -- SNPs Different ‘alleles’ The environment selects among but does not create variations! Genetic Variation & Evolution 6

Do organisms always produce more offspring than can survive? Cichlides: 250, 000 eggs Carmagnola Grey rabbit: 5 -8 litters x 7 offspring Genetic Variation & Evolution Humans: 2 - 7 children/family 7

How does Darwin’s ‘Natural Selection’ explain giraffe evolution? Unlike Lamarcke, traits must be genetically determined The environment creates “Selective Pressures” Which select for best adapted traits An “Adaptation” = a trait selected for by the environment Genetic Variation & Evolution 8

What are examples of environmental selective pressures? Predator-prey interactions Competition for resources Habitat changes!! (Natural or anthropgenic Natural selection acts upon existing genetic variation -- theory is not ‘teleological” -- no purpose, plan, or intent Wrong: “In order to hide from predators, the dead-leaf butterfly evolved a leaf-like appearance. ” “The dead-leaf butterfly wanted to be better camouflaged and evolved a leaf-like appearance. ” “Butterflies mutated because of predation and began To look more like a dead leaf. ” Correct: “Predation selected for butterflies that most resembled a dead leaf. ” Genetic Variation & Evolution l 9

What are the effects of Natural Selection on a population? (20. 7) “Microevolution” vs “Macorevolution” Genetic Variation & Evolution 10

What is the effect of Directional Selection on a population? Progressive change in a trait within a species Genetic Variation & Evolution 11

How does Disruptive Selection affect a population? Responsible for divergence of a single species into two different species Modern example of process: blackbellied seedcracker Genetic Variation & Evolution 12

How does Stabilizing Selection affect a population? Human birth weight & Eurosta gall size Stabilizing selection & ‘living fossils’ Genetic Variation & Evolution 13

What is ‘Artificial Selection’? All these crops are varieties of the species Brassica napa Colors represent different genetic types. Map shows genetic variation in Africa. Genetic Variation & Evolution 14

Why can artificial selection cause genetic problems? species -- in breeding -- founder effect -- harmful recessive traits non-inbred Zebra lived died 20 7 3 2 Eld’s deer lived died 13 4 0 7 Giraffe lived died 11 3 2 3 Oryx lived died 35 2 0 5 Dorcas gazelle lived died 36 14 17 25 From Klug & Cumminings Genetics 5 th ed Genetic Variation & Evolution 15

Why won’t humans evolve wings? Limits of Selection Existence of genetic variation Complex traits involve many genes Suitable selective pressures Genes have multiple effects -- developmental genes Are humans still evolving? Genetic Variation & Evolution 16

What is the evidence for evolution? (Chapter 21) • Observations of evolution • Paleontology & Fossil records • Anatomic evidence • Molecular evidence Evolution II 17

Observations of evolution Peppered moths -- Industrial melanism -- and its reversal Evolution II 18

Other Examples Wheat ( ~ 9 K yrs ) Banana moths in Hawaii (1000 yrs) Faroe Island house mouse (250 yrs) Copapod of the Salton Sea, CA (30 yrs) Drosophila paulistorum (a few yrs in a lab) Evolution II 19

Paleontology What does the fossil record show? Extinct life forms Sequential appearance of derived characteristics Transitional forms What are some limitations of the fossil record? Ambulocetus natans (c. 50 Ma) – which means "walking whale that swims Habitat Geologic disruption Soft-bodied organisms Evolution II 20

How are fossils dated? Principle of “superposition” -- relative dating Radioisotope dating (absolute dating) half-life 14 C 14 N -- 5, 730 years (useful to ~ 60 K yrs BP) 234 U 40 K 230 TH, ~ 80, 000 years 40 Ar ~ 1. 3 Billion yrs Evolution II 21

Anatomical evidence What type of evidence does anatomy reveal? Derived traits have similar anatomy “homologous structures” But “Convergent evolution’ occurs independent evolution “analogous structures” Why does this occur? Distinguishing homologous and analogous traits is not always easy A platypus has fur, a bill, webbed feet, and lays eggs Evolution II 22

Anatomical Evidence, con’t. What does this mean: “Ontogeny reciprocates Phylogeny”? Ernst Haekel’s original data is somewhat flawed What are vestigial structures? What are vestigial genes? -- gene for stripes in horses -- genes for teeth in birds See Wikipedia for other cool examples http: //en. wikipedia. org/wiki/Vestigial Evolution II Human coccyx 23

Anatomical Evidence, con’t. Intelligent design – not! Human pelvis External Testis Eye? Why? Evolution II Human coccyx 24

Molecular Evidence Comparison of DNA (base) and protein (amino acid) sequences DNA base sequence codes for protein amino acid sequence Changes in DNA sequences can be used as a Molecular Clock -- need to know rate of mutation -- can estimate when two species diverged From a common ancestor Evolution II Cytochrome-c base substitutions 25

Chapter 26 and 22: Biological Classification and the Nature of Species Biological classification system: Domain Kingdom Phylum Class Order Family Genus Species Carolus Linnaeus developed system for classifying life and giving each a unique name We know include “Domains” Evolution II 26

Scientific naming of species Scientific binomial – Carolus Linnaeus Genus + Species Homo sapiens vs “humans” Acer rubrum “red maple” vs Biological classification system: Domain Kingdom Phylum Class Order Family Genus Species Writing Conventions So, what is a species? ? Which of these is Acer rubrum? “A group of interbreeding organisms that are reproductively isolated” What is ‘reproductive isolation’? Evolution II 27

What are some mechanisms of reproductive isolation? Pre-zygotic Ecological (habitat) e. g. , mountain ranges Mechanical e. g. reproductive anatomy Temporal e. g. mating seasons Behavioral e. g. , mating rituals Gametic gametes incompatible (many plants) Bowerbirds e. g. , frogs of Sierra Nevada foothills e. g. , bowerbirds of Australia Evolution II 28

Mechanisms of reproductive isolation, con’t. Post-zygotic Hybrid inviability -- embryo / fetus does not develop e. g. , cattle and water buffalo Hybrid infertility -- offspring is infertile e. g. , colored and pied flycatchers Question Evolution II Meet and hybridize in central and northern Europe 29

The biological species concept has limitations If two species can hybridize, are they separate species? -- plants -- animals Native: California Tiger Salamander Invasive: Adult Barred Tiger Hybrid: Appears to be more fit then native Should all dogs be classified in the same species? http: //sciencemode. com/2007/09/20/calif ornia-barred-tigersalamandersinterbreed-producehybrids/ Evolution II 30

How does geographic distribution relate to speciation? Allopatric speciation: Original species is split by geographic isolation -- mountains, rivers, islands Different species remain after barrier is gone How does Sympatric speciation occur? e. g. , “blackbellied seedcracker” Environment selects for 2 different forms A less fit hybrid “reinforces” divergence Question Evolution II 31

Temporal isolation explains origin of the apple maggot Apple Maggot Hawthorn Apple Visit Martin G. Kelly’s site at http: //www. sciencecases. org/maggot_fly. asp Evolution II 32

Under what conditions does ‘Adaptive Radiation’ occur? -A special case of disruptive evolution Darwin’s Finches -- classic example Can occur regionally or globally -- rise of mammals Adaptations reinforced by “Character Displacement’ Question Evolution II 33

Plotting macroevolution What are some characteristics of evolution that can be diagrammed? Gradualism vs ‘punctuated equilibrium’ Stephen J Gould & Niles Eldredge What are possible mechanisms of rapid speciation? -- polyploidy -- mutations to developmental genes -- geologic time vs ‘human’ time Evolution II 34

Plotting evolutionary relationships (from Chapter 23) The traditional “evolutionary tree” vs Claudistics Clade= all organisms with “Shared derived characteristics” Evolution II 35

Highlights of the History of Life (from Chapter 26) Advanced life forms have appeared Late in earth’s geologic history Origin of life ~ 3. 8 bya Eukaryotic cells ~ 1. 7 bya Multicellular organisms ~ 1. 2 bya Origin of life Multicellular organisms Humans only ~ 1 mya Evolution II 36

The origin of major groups of animals The ‘eras’ The Cambrian explosion Vertebrates Invertebrates Age of reptiles Age of mammals Insects most successful of them all Evolution II 37

There have been many mass extinctions! Some small, Some BIG! Question Evolution II 38