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(2) Scala Naturae and Classification of Species • The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae • The Old Testament holds that species were individually designed by God and therefore perfect. • Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose • Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Ideas About Change over Time. Fig. 22-3. • The study of fossils helped to lay the groundwork for Darwin’s ideas • Fossils are remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers or strata. Layers of deposited sediment. Younger stratum with more recent fossils. Video: Grand Canyon. Older stratum with older fossils. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. • Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier • Cuvier advocated catastrophism, speculating that each boundary between strata represents a catastrophe. • Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today • Lyell’s principle of uniformitarianism states that the mechanisms of change are constant over time • This view strongly influenced Darwin’s thinking. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
(3) Lamarck s Hypothesis of Evolution • Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics • The mechanisms he proposed are unsupported by evidence. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. •. modification by natural selection explains the adaptations of organisms and the unity and As the 19th century dawned, it was diversity of life. generally believed that species had remained unchanged since their creation • However, a few doubts about the permanence of species were beginning to arise. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Darwin’s Research. The Voyage of the Beagle. • As a boy and into adulthood, Charles Darwin had a consuming interest in nature • Darwin first studied medicine (unsuccessfully), and then theology at Cambridge University • After graduating, he took an unpaid position as naturalist and companion to Captain Robert FitzRoy for a 5-year around the world voyage on the Beagle. • During his travels on the Beagle, Darwin collected specimens of South American plants and animals • He observed adaptations of plants and animals that inhabited many diverse environments • Darwin was influenced by Lyell’s Principles of Geology and thought that the earth was more than 6000 years old. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Fig. 22-5. GREAT BRITAIN. ATLANTIC OCEAN The Galápagos Islands. AFRICA Pinta Genovesa Marchena Santiago. Fernandina Isabela. Santa Santa Cruz Fe. AUSTRALIA PACIFIC OCEAN. San Cristobal. Equator. SOUTH AMERICA. Daphne Islands. Pinzón. Florenza. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. EUROPE. NORTH AMERICA. Andes. • His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America. Cape of Good Hope Tasmania. Española. Cape Horn Tierra del Fuego. New Zealand.
(4) Darwin’s Focus on Adaptation Video: Galá Galápagos Islands Overview Video: BlueBlue-footed Boobies Courtship Ritual Video: Albatross Courtship Ritual Video: Galá Galápagos Sea Lion Video: Soaring Hawk Video: Galá Galápagos Tortoises Video: Galá Galápagos Marine Iguana. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. • In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes • From studies made years after Darwin’s voyage, biologists have concluded that this is indeed what happened to the Galápagos finches. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Fig. 22-6. (a) Cactus-eater. (c) Seed-eater. (b) Insect-eater. • In 1844, Darwin wrote an essay on the origin of species and natural selection but did not introduce his theory publicly, anticipating an uproar • In June 1858, Darwin received a manuscript from Alfred Russell Wallace, who had developed a theory of natural selection similar to Darwin’s • Darwin quickly finished The Origin of Species and published it the next year Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. The Origin of Species • Darwin developed two main ideas: – Descent with modification explains life’s unity and diversity – Natural selection is a cause of adaptive evolution. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Descent with Modification • Darwin never used the word evolution in the first edition of The Origin of Species • The phrase descent with modification summarized Darwin’s perception of the unity of life • The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
(5) Fig. 22-7. • In the Darwinian view, the history of life is like a tree with branches representing life’s diversity • Darwin’s theory meshed well with the hierarchy of Linnaeus. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Fig. 22-8. Fig. 22-8a Hyracoidea (Hyraxes). Platybelodon. Sirenia (Manatees and relatives) Moeritherium. Stegodon Barytherium. Deinotherium. Mammuthus. Mammut. Elephas maximus (Asia). Platybelodon. Stegodon. Loxodonta africana (Africa). Mammuthus. Elephas maximus (Asia). Loxodonta cyclotis (Africa). Loxodonta africana (Africa). 24. Millions of years ago. 5.5. 24. 34. Loxodonta cyclotis (Africa) 34. 5.5. 2 104 0 Years ago. Millions of years ago. 2 104 0. Years ago. Artificial Selection, Natural Selection, and Adaptation • Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection • Darwin then described four observations of nature and from these drew two inferences. Fig. 22-9. Terminal bud. Lateral buds. Cabbage. Brussels sprouts Flower clusters. Leaves Kale. Cauliflower Stem Wild mustard Flowers and stems Broccoli. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Kohlrabi.
(6) Fig. 22-10. • Observation #1: Members of a population often vary greatly in their traits. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Fig. 22-11. • Observation #2: Traits are inherited from parents to offspring • Observation #3: All species are capable of producing more offspring than the environment can support. Spore cloud. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. • Observation #4: Owing to lack of food or other resources, many of these offspring do not survive. • Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
(7) • Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations. • Darwin was influenced by Thomas Malthus who noted the potential for human population to increase faster than food supplies and other resources • If some heritable traits are advantageous, these will accumulate in the population, and this will increase the frequency of individuals with adaptations • This process explains the match between organisms and their environment. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Fig. 22-12. Natural Selection: A Summary. (a) A flower mantid in Malaysia. • Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals • Natural selection increases the adaptation of organisms to their environment over time • If an environment changes over time, natural selection may result in adaptation to these new conditions and may give Video: Seahorse Camouflage rise to new species. (b) A stick mantid in Africa. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Concept 22.3: Evolution is supported by an overwhelming amount of scientific evidence New discoveries continue to fill the gaps. • Note that individuals do not evolve; populations evolve over time • Natural selection can only increase or decrease heritable traits in a population • Adaptations vary with different environments. •. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. identified by Darwin in The Origin of Species.
(8) Direct Observations of Evolutionary Change. Predation and Coloration in Guppies : Scientific Inquiry. • Two examples provide evidence for natural selection: the effect of differential predation on guppy populations and the evolution of drug-resistant HIV. • John Endler has studied the effects of predators on wild guppy populations • Brightly colored males are more attractive to females • However, brightly colored males are more vulnerable to predation • Guppy populations in pools with fewer predators had more brightly colored males. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Fig. 22-13. Fig. 22-13a. EXPERIMENT Predator: Killifish; preys mainly on juvenile guppies (which do not express the color genes). Experimental transplant of guppies. Pools with killifish, but no guppies prior to transplant. Guppies: Adult males have brighter colors than those in “pike-cichlid pools”. EXPERIMENT Predator: Killifish; preys mainly on juvenile guppies (which do not express the color genes). Predator: Pike-cichlid; preys mainly on adult guppies Guppies: Adult males are more drab in color than those in “killifish pools”. Experimental transplant of guppies. Guppies: Adult males have brighter colors than those in “pike-cichlid pools”. Pools with killifish, but no guppies prior to transplant. RESULTS 12 Number of colored spots. Area of colored spots (mm2). 12 10 8 6 4 2 0. Source population. 10. Transplanted population. 8. Predator: Pike-cichlid; preys mainly on adult guppies. 6. Guppies: Adult males are more drab in color than those in “killifish pools”. 4 2 0. Source Transplanted population population. Fig. 22-13b. RESULTS 12 Number of colored spots. Area of colored spots (mm2). 12 10 8 6 4 2 0. Source Transplanted population population. 10 8 6 4 2 0. Source Transplanted population population. • Endler transferred brightly colored guppies (with few predators) to a pool with many predators • As predicted, over time the population became less brightly colored • Endler also transferred drab colored guppies (with many predators) to a pool with few predators • As predicted, over time the population became more brightly colored Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
(9) The Evolution of Drug-Resistant HIV • The use of drugs to combat HIV selects for viruses resistant to these drugs • HIV uses the enzyme reverse transcriptase to make a DNA version of its own RNA genome • The drug 3TC is designed to interfere and cause errors in the manufacture of DNA from the virus. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. • Some individual HIV viruses have a variation that allows them to produce DNA without errors • These viruses have a greater reproductive success and increase in number relative to the susceptible viruses • The population of HIV viruses has therefore developed resistance to 3TC • The ability of bacteria and viruses to evolve rapidly poses a challenge to our i t Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Percent of HIV resistant to 3TC. Fig. 22-14. 100. Patient No. 1. • Natural selection does not create new traits, but edits or selects for traits already present in the population • The local environment determines which traits will be selected for or selected against in any specific population. Patient No. 2. 75. 50 Patient No. 3. 25. 0 0. 2. 4. 6. 8. 10. 12. Weeks Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. The Fossil Record. Fig. 22-15. 0 2 4 4. Depth (meters). • The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time. 3. 6. 4 Bristolia insolens. 8. 3 Bristolia bristolensis. 10 12 14. 2 Bristolia harringtoni. 16 18 1 Bristolia mohavensis. 3 2. 1 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Latham Shale dig site, San Bernardino County, California.
(10) Fig. 22-16. • The Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record • Paleontologists have discovered fossils of many such transitional forms. (a) Pakicetus (terrestrial). (b) Rhodocetus (predominantly aquatic). Pelvis and hind limb (c) Dorudon (fully aquatic). Pelvis and hind limb (d) Balaena (recent whale ancestor) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Anatomical and Molecular Homologies. Homology • Homology is similarity resulting from common ancestry. • Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Fig. 22-17. • Comparative embryology reveals anatomical homologies not visible in adult organisms. Humerus Radius Ulna Carpals Metacarpals Phalanges Human. Cat. Whale. Bat. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
(11) Fig. 22-18. • Vestigial structures are remnants of features that served important functions in the organism’s ancestors • Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor. Pharyngeal pouches. Post-anal tail. Chick embryo (LM). Human embryo. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Homologies and “Tree Thinking”. Fig. 22-19. Branch point (common ancestor) Lungfishes. Mammals. 2 Tetrapod limbs Amnion. Lizards and snakes. 3 4. Homologous characteristic. Crocodiles. Ostriches. 6 Feathers. Birds. 5. Hawks and other birds. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Convergent Evolution • Convergent evolution is the evolution of similar, or analogous, features in distantly related groups • Analogous traits arise when groups independently adapt to similar environments in similar ways • Convergent evolution does not provide information about ancestry. Fig. 22-20. Sugar glider. NORTH AMERICA. AUSTRALIA. Flying squirrel Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Tetrapods. Amphibians. 1. Amniotes. • The Darwinian concept of an evolutionary tree of life can explain homologies • Evolutionary trees are hypotheses about the relationships among different groups • Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data.
(12) Biogeography • Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution • Islands have many endemic species that are often closely related to species on the nearest mainland or island. • Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift • An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. What Is Theoretical About Darwin’s View of Life? • In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena • Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions • Ongoing research adds to our understanding of evolution. Fig. 22-UN1. Observations Individuals in a population vary in their heritable characteristics.. Inferences Individuals that are well suited to their environment tend to leave more offspring than other individuals and Over time, favorable traits accumulate in the population.. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Fig. 22-UN2. Organisms produce more offspring than the environment can support.. Fig. 22-UN3.
(13) Overview: The Smallest Unit of Evolution. Fig. 23-1. • One misconception is that organisms evolve, in the Darwinian sense, during their lifetimes • Natural selection acts on individuals, but only populations evolve • Genetic variations in populations contribute to evolution • Microevolution is a change in allele frequencies in a population over generations. p reproduction produce the genetic variation that makes evolution • Two processes,possible mutation and sexual reproduction, produce the variation in gene pools that contributes to differences among individuals. Fig. 23-2. (a). Genetic Variation • Variation in individual genotype leads to variation in individual phenotype • Not all phenotypic variation is heritable • Natural selection can only act on variation with a genetic component. Variation Within a Population (b). • Both discrete and quantitative characters contribute to variation within a population • Discrete characters can be classified on an either-or basis • Quantitative characters vary along a continuum within a population.
(14) Variation Between Populations • Population geneticists measure polymorphisms in a population by determining the amount of heterozygosity at the gene and molecular levels • Average heterozygosity measures the average percent of loci that are heterozygous in a population • Nucleotide variability is measured by comparing the DNA sequences of pairs of individuals. • Most species exhibit geographic variation, differences between gene pools of separate populations or population subgroups. Fig. 23-3. 1. 2.4. 8.11. 9.12. 3.14. 5.18. 10.16 13.17. 6. 7.15. 19. XX. • Some examples of geographic variation occur as a cline, which is a graded change in a trait along a geographic axis. 1. 2.19. 3.8. 4.16 5.14. 9.10 11.12 13.17 15.18. 6.7 XX. Fig. 23-4. Mutation. Ldh-B b allele frequency. 1.0 0.8. • Mutations are changes in the nucleotide sequence of DNA • Mutations cause new genes and alleles to arise • Only mutations in cells that produce gametes can be passed to offspring. 0.6 0.4 0.2 0 46. 44. Maine Cold (6°C). 42. 40. 38 36 Latitude (°N). 34. 32. 30. Georgia Warm (21°C). Animation: Genetic Variation from Sexual Recombination.
(15) Point Mutations • A point mutation is a change in one base in a gene. • The effects of point mutations can vary: – Mutations in noncoding regions of DNA are often harmless – Mutations in a gene might not affect protein production because of redundancy in the genetic code. Mutations That Alter Gene Number or Sequence • The effects of point mutations can vary: – Mutations that result in a change in protein production are often harmful – Mutations that result in a change in protein production can sometimes increase the fit between organism and environment. Mutation Rates • Mutation rates are low in animals and plants • The average is about one mutation in every 100,000 genes per generation • Mutations rates are often lower in prokaryotes and higher in viruses. • Chromosomal mutations that delete, disrupt, or rearrange many loci are typically harmful • Duplication of large chromosome segments is usually harmful • Duplication of small pieces of DNA is sometimes less harmful and increases the genome size • Duplicated genes can take on new functions by further mutation. Sexual Reproduction • Sexual reproduction can shuffle existing alleles into new combinations • In organisms that reproduce sexually, recombination of alleles is more important than mutation in producing the genetic differences that make adaptation possible.
(16) Weinberg equation can be used to test whether a population is • The first step inevolving testing whether evolution is occurring in a population is to clarify what we mean by a population. • A population is a localized group of individuals capable of interbreeding and producing fertile offspring • A gene pool consists of all the alleles for all loci in a population • A locus is fixed if all individuals in a population are homozygous for the same allele. ALASKA. CANADA. Beaufort Sea. Porcupine herd range. MAP AREA. T ES S HW RIE RT ITO NO RR TE. Porcupine herd range. T ES ES HW RI RT ITO NO RR TE. Beaufort Sea. MAP AREA. CANADA. Fig. 23-5a. Porcupine herd ALASKA. Fig. 23-5. Gene Pools and Allele Frequencies. Fortymile herd. • The frequency of an allele in a population can be calculated – For diploid organisms, the total number of alleles at a locus is the total number of individuals x 2 – The total number of dominant alleles at a locus is 2 alleles for each homozygous dominant individual plus 1 allele for each heterozygous individual; the same logic applies for recessive alleles. Fortymile herd range ALASKA YUKON. ALASKA YUKON. Fortymile herd range. • By convention, if there are 2 alleles at a locus, p and q are used to represent their frequencies • The frequency of all alleles in a population will add up to 1 – For example, p + q = 1.
(17) The Hardy-Weinberg Principle. Hardy-Weinberg Equilibrium. • The Hardy-Weinberg principle describes a population that is not evolving • If a population does not meet the criteria of the Hardy-Weinberg principle, it can be concluded that the population is evolving. • The Hardy-Weinberg principle states that frequencies of alleles and genotypes in a population remain constant from generation to generation • In a given population where gametes contribute to the next generation randomly, allele frequencies will not change • Mendelian inheritance preserves genetic variation in a population. Fig. 23-6. Alleles in the population Frequencies of alleles Gametes produced. p = frequency of = 0.8 CR allele q = frequency of CW allele = 0.2. Each egg:. Each sperm:. 80% 20% chance chance. 80% 20% chance chance. • Hardy-Weinberg equilibrium describes the constant frequency of alleles in such a gene pool • If p and q represent the relative frequencies of the only two possible alleles in a population at a particular locus, then – p2 + 2pq + q2 = 1 – where p2 and q2 represent the frequencies of the homozygous genotypes and 2pq represents the frequency of the heterozygous genotype. 80% CR (p = 0.8). 20% CW (q = 0.2). Sperm CR (80%). Fig. 23-7-2. 64% CRCR, 32% CRCW, and 4% CWCW. CW (20%). CR (80%). Eggs. Gametes of this generation: 64%. 64% (p2) CRCR. CW (20%). Fig. 23-7-1. 16% (qp) CRCW. CR. 4% CW q. 16% (pq) CRCW 4% (q2) CW CW. +. 16% CR. +. 16% CW. = 80% CR = 0.8 = p = 20% CW. = 0.2 =.
(18) Fig. 23-7-3. Fig. 23-7-4. 64% CRCR, 32% CRCW, and 4% CWCW. Sperm CR (80%). 4% CW q. +. 16% CR. +. 16% CW. = 80% CR = 0.8 = p = 20% CW. = 0.2 =. CR (80%). CW (20%). 16% ( pq) CR CW. 64% ( p2) CR CR CW (20%). 64%. Eggs. Gametes of this generation: CR. 20% CW (q = 0.2). 80% CR ( p = 0.8). 16% (qp) CR CW. 4% (q2) CW CW. 64% CR CR, 32% CR CW, and 4% CW CW. Genotypes in the next generation:. Gametes of this generation: 64% CR 4% CW. 64% CRCR, 32% CRCW, and 4% CWCW plants. + +. 16% CR 16% CW. = 80% CR = 0.8 = p = 20% CW = 0.2 = q. Genotypes in the next generation:. 64% CR CR, 32% CR CW, and 4% CW CW plants. Conditions for Hardy-Weinberg Equilibrium • The Hardy-Weinberg theorem describes a hypothetical population • In real populations, allele and genotype frequencies do change over time. • The five conditions for nonevolving populations are rarely met in nature: – No mutations – Random mating – No natural selection – Extremely large population size – No gene flow. Applying the Hardy-Weinberg Principle • Natural populations can evolve at some loci, while being in Hardy-Weinberg equilibrium at other loci. • We can assume the locus that causes phenylketonuria (PKU) is in HardyWeinberg equilibrium given that: – The PKU gene mutation rate is low – Mate selection is random with respect to whether or not an individual is a carrier for the PKU allele.
(19) – Natural selection can only act on rare homozygous individuals who do not follow dietary restrictions – The population is large – Migration has no effect as many other populations have similar allele frequencies. • The occurrence of PKU is 1 per 10,000 births – q2 = 0.0001 – q = 0.01. • The frequency of normal alleles is – p = 1 – q = 1 – 0.01 = 0.99. • The frequency of carriers is – 2pq = 2 x 0.99 x 0.01 = 0.0198 – or approximately 2% of the U.S. population. p , genetic drift, and gene flow can alter allele frequencies in a population • Three major factors alter allele frequencies and bring about most evolutionary change:. Natural Selection • Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions. – Natural selection – Genetic drift – Gene flow. Genetic Drift • The smaller a sample, the greater the chance of deviation from a predicted result • Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next • Genetic drift tends to reduce genetic variation through losses of alleles Animation: Causes of Evolutionary Change. Fig. 23-8-1. CR CR. CR CR CR CW. CR CR. CW CW. CR CW. CR CR CR CR. CR CW CR CW. Generation 1 p (frequency of CR) = 0.7 q (frequency of CW ) = 0.3.
(20) Fig. 23-8-2. Fig. 23-8-3. CR CR. CR CR. CW CW. CR CW. CR CR. CW CW. CR CW CR CW. Generation 1 p (frequency of CR) = 0.7 q (frequency of CW ) = 0.3. CW CW. CR CW. CW CW. CR CW. CR CW. CR CR. CR CW. CR CR. CR CW CR CW. Generation 1 p (frequency of CR) = 0.7 q (frequency of CW ) = 0.3. Generation 2 p = 0.5 q = 0.5. CW CW. CR CW. CR CR CR CR. CW CW. CR CR. CR CW. CR CR. CR CR CR CW. CR CR. CW CW. CR CW. CR CR. CR CR. CR CR. CW CW. CR CR. CR CW. CR CR. CR CR CR CW. CR CR. CR CR. CR CR. CR CR. CR CR CR CR. CR CR CR CW. Generation 2 p = 0.5 q = 0.5. CR CR. CR CR. Generation 3 p = 1.0 q = 0.0. The Founder Effect. The Bottleneck Effect. • The founder effect occurs when a few individuals become isolated from a larger population • Allele frequencies in the small founder population can be different from those in the larger parent population. • The bottleneck effect is a sudden reduction in population size due to a change in the environment • The resulting gene pool may no longer be reflective of the original population’s gene pool • If the population remains small, it may be further affected by genetic drift. Fig. 23-9. • Understanding the bottleneck effect can increase understanding of how human activity affects other species. Original population. Bottlenecking event. Surviving population.
(21) •. Case Study: Impact of Genetic Drift on the Greater Prairie Chicken Loss of prairie habitat caused a severe. Fig. 23-10 Pre-bottleneck Post-bottleneck (Illinois, 1820) (Illinois, 1993). Range of greater prairie chicken. reduction in the population of greater prairie chickens in Illinois • The surviving birds had low levels of genetic variation, and only 50% of their eggs hatched. (a). Population size. Location. Percentage Number of alleles of eggs per locus hatched. Illinois 1930–1960s. 1,000–25,000. 5.2. 93. <50. 3.7. <50. Kansas, 1998 (no bottleneck). 750,000. 5.8. 99. Nebraska, 1998 (no bottleneck). 75,000– 200,000. 5.8. 96. Minnesota, 1998 (no bottleneck). 4,000. 5.3. 85. 1993. (b). Fig. 23-10a. Fig. 23-10b. Population size. Number of alleles per locus. 1,000–25,000. 5.2. 93. <50. 3.7. <50. Kansas, 1998 (no bottleneck). 750,000. 5.8. 99. Nebraska, 1998 (no bottleneck). 75,000– 200,000. 5.8. 96. Minnesota, 1998 (no bottleneck). 4,000. 5.3. 85. Location. Pre-bottleneck (Illinois, 1820). Post-bottleneck (Illinois, 1993). Illinois 1930–1960s 1993. (a). Range of greater prairie chicken. Percentage of eggs hatched. (b). Effects of Genetic Drift: A Summary • Researchers used DNA from museum specimens to compare genetic variation in the population before and after the bottleneck • The results showed a loss of alleles at several loci • Researchers introduced greater prairie chickens from population in other states and were successful in introducing new alleles and increasing the egg hatch rate to 90%. 1. Genetic drift is significant in small populations 2. Genetic drift causes allele frequencies to change at random 3. Genetic drift can lead to a loss of genetic variation within populations 4. Genetic drift can cause harmful alleles to become fixed.
(22) Fig. 23-11. Gene Flow • Gene flow consists of the movement of alleles among populations • Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen) • Gene flow tends to reduce differences between populations over time • Gene flow is more likely than mutation to alter allele frequencies directly. Fig. 23-12. Fig. 23-12a. Index of copper tolerance. 60. MINE SOIL. NONMINE SOIL. 50. NONMINE SOIL Prevailing wind direction. 40 30 20 10 0 20. 0. 20. 0 100 20 40 60 80 Distance from mine edge (meters). 120. 140. 160. MINE SOIL. NONMINE SOIL. NONMINE SOIL. 50. Prevailing wind direction. 40 30 20 10 0 20. 0. 20. 0. 20. 40. 60. 80. Distance from mine edge (meters). Fig. 23-12b. 70 60. 70 Index of copper tolerance. • Gene flow can decrease the fitness of a population • In bent grass, alleles for copper tolerance are beneficial in populations near copper mines, but harmful to populations in other soils • Windblown pollen moves these alleles between populations • The movement of unfavorable alleles into a population results in a decrease in fit between organism and environment. 100. 120. 140. 160.
(23) • Gene flow can increase the fitness of a population • Insecticides have been used to target mosquitoes that carry West Nile virus and malaria • Alleles have evolved in some populations that confer insecticide resistance to these mosquitoes • The flow of insecticide resistance alleles into a population can cause an increase in fitness. A Closer Look at Natural Selection • Natural selection brings about adaptive evolution by acting on an organism’s phenotype. •. p the only mechanism that consistently causes adaptive evolution Only natural selection consistently results in adaptive evolution. Relative Fitness • The phrases “struggle for existence” and “survival of the fittest” are misleading as they imply direct competition among individuals • Reproductive success is generally more subtle and depends on many factors. Directional, Disruptive, and Stabilizing Selection • Relative fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals • Selection favors certain genotypes by acting on the phenotypes of certain organisms. • Three modes of selection: – Directional selection favors individuals at one end of the phenotypic range – Disruptive selection favors individuals at both extremes of the phenotypic range – Stabilizing selection favors intermediate variants and acts against extreme phenotypes.
(24) Original Evolved population population. Frequency of individuals. Fig. 23-13a. Frequency of individuals. Fig. 23-13. Original population. Original population. Phenotypes (fur color). Phenotypes (fur color). Original population Evolved population. (a) Directional selection. (b) Disruptive selection. (c) Stabilizing selection. (a) Directional selection. Frequency of individuals. Fig. 23-13c. Frequency of individuals. Fig. 23-13b. Original population. Original population. Phenotypes (fur color). Phenotypes (fur color). Evolved population Evolved population. (c) Stabilizing selection. (b) Disruptive selection. The Key Role of Natural Selection in Adaptive Evolution • Natural selection increases the frequencies of alleles that enhance survival and reproduction • Adaptive evolution occurs as the match between an organism and its environment increases. Fig. 23-14. (a) Color-changing ability in cuttlefish. Movable bones. (b) Movable jaw bones in snakes.
(25) Fig. 23-14a. Fig. 23-14b. Movable bones. (a) Color-changing ability in cuttlefish (b) Movable jaw bones in snakes. Sexual Selection • Because the environment can change, adaptive evolution is a continuous process • Genetic drift and gene flow do not consistently lead to adaptive evolution as they can increase or decrease the match between an organism and its environment. • Sexual selection is natural selection for mating success • It can result in sexual dimorphism, marked differences between the sexes in secondary sexual characteristics. Fig. 23-15. • Intrasexual selection is competition among individuals of one sex (often males) for mates of the opposite sex • Intersexual selection, often called mate choice, occurs when individuals of one sex (usually females) are choosy in selecting their mates • Male showiness due to mate choice can increase a male’s chances of attracting a female, while decreasing his chances of survival.
(26) Fig. 23-16 EXPERIMENT. • How do female preferences evolve? • The good genes hypothesis suggests that if a trait is related to male health, both the male trait and female preference for that trait should be selected for. Female gray tree frog SC male gray tree frog. LC male gray tree frog. SC sperm × Eggs ×. LC sperm. Offspring of Offspring of SC father LC father. Fitness of these half-sibling offspring compared. RESULTS. Fitness Measure. 1995. 1996. Larval growth. NSD. Larval survival. LC better. NSD. Time to metamorphosis. LC better (shorter). LC better (shorter). LC better. NSD = no significant difference; LC better = offspring of LC males superior to offspring of SC males.. Fig. 23-16a. Fig. 23-16b. EXPERIMENT. RESULTS. Fitness Measure Female gray tree frog LC male gray tree frog. SC male gray tree frog SC sperm × Eggs × LC sperm. Offspring of Offspring of LC father SC father. 1995 NSD. Larval growth. 1996. LC better. Larval survival. LC better. NSD. Time to metamorphosis. LC better (shorter). LC better (shorter). NSD = no significant difference; LC better = offspring of LC males superior to offspring of SC males.. Fitness of these half-sibling offspring compared. The Preservation of Genetic Variation • Various mechanisms help to preserve genetic variation in a population. Diploidy • Diploidy maintains genetic variation in the form of hidden recessive alleles.
(27) Balancing Selection • Balancing selection occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population. Heterozygote Advantage. • Heterozygote advantage occurs when heterozygotes have a higher fitness than do both homozygotes • Natural selection will tend to maintain two or more alleles at that locus • The sickle-cell allele causes mutations in hemoglobin but also confers malaria resistance. Fig. 23-17. Frequency-Dependent Selection. Frequencies of the sickle-cell allele 0–2.5%. Distribution of malaria caused by Plasmodium falciparum (a parasitic unicellular eukaryote). 2.5–5.0% 5.0–7.5% 7.5–10.0% 10.0–12.5%. • In frequency-dependent selection, the fitness of a phenotype declines if it becomes too common in the population • Selection can favor whichever phenotype is less common in a population. >12.5%. Fig. 23-18. Fig. 23-18a. “Right-mouthed”. Frequency of “left-mouthed” individuals. 1.0. “Left-mouthed”. “Right-mouthed”. 0.5. “Left-mouthed” 0. 1981 ’82 ’83 ’84 ’85 ’86 ’87 ’88 ’89 ’90 Sample year.
(28) Fig. 23-18b. Neutral Variation. Frequency of “left-mouthed” individuals. 1.0. • Neutral variation is genetic variation that appears to confer no selective advantage or disadvantage • For example,. 0.5. – Variation in noncoding regions of DNA – Variation in proteins that have little effect on protein function or reproductive fitness 0. 1981 ’82 ’83 ’84 ’85 ’86 ’87 ’88 ’89 ’90 Sample year. Why Natural Selection Cannot Fashion Perfect Organisms. Fig. 23-19. 1. Selection can act only on existing variations 2. Evolution is limited by historical constraints 3. Adaptations are often compromises 4. Chance, natural selection, and the environment interact. Fig. 23-UN1. Fig. 23-UN2. Sampling sites (1–8 represent pairs of sites). Original population. Evolved population. 2. 1. 3. 4. 5. 6. 7. 8. 9. 10. 11. Allele frequencies lap94 alleles. Other lap alleles. Data from R.K. Koehn and T.J. Hilbish, The adaptive importance of genetic variation, American Scientist 75:134–141 (1987).. Salinity increases toward the open ocean. 3 Long Island 2. Directional selection. Disruptive selection. 1. Stabilizing selection. Sound 9. N W. 10. E S. 8 6 7 4 5. 11. Atlantic Ocean.
(29) Fig. 23-UN3. •. Overview: That “Mystery of Mysteries” In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth. Video: Galá Galápagos Tortoise. Fig. 24-1. • Speciation, the origin of new species, is at the focal point of evolutionary theory • Evolutionary theory must explain how new species originate and how populations evolve • Microevolution consists of adaptations that evolve within a population, confined to one gene pool • Macroevolution refers to evolutionary change above the species level Animation: Macroevolution. Concept 24.1: The biological species concept emphasizes reproductive isolation • Species is a Latin word meaning “kind” or “appearance” • Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms. The Biological Species Concept • The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations • Gene flow between populations holds the phenotype of a population together.
(30) Fig. 24-2. Fig. 24-3. EXPERIMENT Example of a gene tree for population pair A-B Allele Gene flow event. (a) Similarity between different species. Population. 1. B. 2. A. 3. A. 4. A. 5. B. 6. B. 7. B. Allele 1 is more closely related to alleles 2, 3, and 4 than to alleles 5, 6, and 7. Inference: Gene flow occurred.. Alleles 5, 6, and 7 are more closely related to one another than to alleles in population A. Inference: No gene flow occurred.. RESULTS Pair of populations with detected gene flow. (b) Diversity within a species. Fig. 24-3a. Estimated minimum number of gene flow events to account for genetic patterns. Distance between populations (km). A-B. 5. 340. K-L. 3. 720. A-C. 2–3. 1,390. B-C. 2. 1,190. F-G. 2. 760. G-I. 2. 1,110. C-E. 1–2. 1,310. Fig. 24-3b. RESULTS. EXPERIMENT Example of a gene tree for population pair A-B Allele Population Gene flow event. 1. B. 2. A. 3. A. 4. A B. 5 6. B. 7. B. Fig. 24-3c. Allele 1 is more closely related to alleles 2, 3, and 4 than to alleles 5, 6, and 7. Inference: Gene flow occurred.. Alleles 5, 6, and 7 are more closely related to one another than to alleles in population A. Inference: No gene flow occurred.. Pair of populations with detected gene flow. Estimated minimum number of gene flow events to account for genetic patterns. Distance between populations (km). A-B. 5. K-L. 3. A-C. 2–3. 1,390. B-C. 2. 1,190. F-G. 2. 760. G-I. 2. 1,110. C-E. 1–2. 1,310. 340 720. Reproductive Isolation • Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring • Hybrids are the offspring of crosses between different species • Reproductive isolation can be classified by whether factors act before or after fertilization. Grey-crowned babblers.
(31) • Prezygotic barriers block fertilization from occurring by: – Impeding different species from attempting to mate – Preventing the successful completion of mating – Hindering fertilization if mating is successful. Fig. 24-4. • Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers. Fig. 24-4a Prezygotic barriers Habitat Isolation. Prezygotic barriers Habitat Isolation. Temporal Isolation. Individuals of different species. Mechanical Isolation. Gametic Isolation. Mating attempt. (c). (a). (e). (f). Reduced Hybrid Viability. Reduced Hybrid Fertility. (h). Viable, fertile offspring. (d). (i). Mating attempt. Hybrid Breakdown. Fertilization. (g). Mechanical Isolation. Behavioral Isolation. Individuals of different species. Postzygotic barriers. Behavioral Isolation. Temporal Isolation. (a). (e). (c). (f). (l). (j). (b). (d) (k). (b). Fig. 24-4i. Fig. 24-4b. Prezygotic barriers. Gametic Isolation. Postzygotic barriers. Reduced Hybrid Viability Reduced Hybrid Fertility. Hybrid Breakdown. Viable, fertile offspring. Fertilization. (g). (h). (i). (l). Prezygotic barriers. Habitat Isolation. (j). (k). Individuals of different species. Temporal Isolation. Behavioral Isolation. Mechanical Isolation. Mating attempt.
(32) Fig. 24-4j. Fig. 24-4c. (a). Postzygotic barriers. Prezygotic barriers Gametic Isolation. Reduced Hybrid Viability. Reduced Hybrid Fertility. Hybrid Breakdown. Viable, fertile offspring. Fertilization. Water-dwelling Thamnophis. Fig. 24-4d. (b). • Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes. Terrestrial Thamnophis. Fig. 24-4e. Fig. 24-4f. (c) (d). Eastern spotted skunk (Spilogale putorius). Western spotted skunk (Spilogale gracilis).
(33) Fig. 24-4g. (e). • Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers. Video: Albatross Courtship Ritual. Courtship ritual of bluefooted boobies. Video: Giraffe Courtship Ritual Video: BlueBlue-footed Boobies Courtship Ritual. Fig. 24-4h. (f). • Mechanical isolation: Morphological differences can prevent successful mating. Bradybaena with shells spiraling in opposite directions. Fig. 24-4k. (g). • Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species. Sea urchins.
(34) • Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult:. • Reduced hybrid viability: Genes of the different parent species may interact and impair the hybrid’s development. – Reduced hybrid viability – Reduced hybrid fertility – Hybrid breakdown. Fig. 24-4l. (h). • Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile. Ensatina hybrid. Fig. 24-4m. Fig. 24-4n. (i). Donkey. (j). Horse.
(35) Fig. 24-4o. (k). • Hybrid breakdown: Some firstgeneration hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile. Mule (sterile hybrid). Fig. 24-4p. (l). Limitations of the Biological Species Concept • The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes). Hybrid cultivated rice plants with stunted offspring (center). Other Definitions of Species • Other species concepts emphasize the unity within a species rather than the separateness of different species • The morphological species concept defines a species by structural features – It applies to sexual and asexual species but relies on subjective criteria. • The ecological species concept views a species in terms of its ecological niche – It applies to sexual and asexual species and emphasizes the role of disruptive selection. • The phylogenetic species concept: defines a species as the smallest group of individuals on a phylogenetic tree – It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species.
(36) •. Concept 24.2: Speciation can take place with or without geographic separation Speciation can occur in two ways:. Fig. 24-5. – Allopatric speciation – Sympatric speciation. (a) Allopatric speciation. Allopatric (“Other Country”) Speciation • In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations. •. (b) Sympatric speciation. The Process of Allopatric Speciation The definition of barrier depends on the. ability of a population to disperse • Separate populations may evolve independently through mutation, natural selection, and genetic drift. Fig. 24-6. •. Evidence of Allopatric Speciation Regions with many geographic barriers typically have more species than do regions with fewer barriers. A. harrisi. A. leucurus.
(37) Fig. 24-7. Fig. 24-7a. Mantellinae (Madagascar only): 100 species Mantellinae (Madagascar only): 100 species. Rhacophorinae (India/Southeast Asia): 310 species. Rhacophorinae (India/Southeast Asia): 310 species. Other Indian/ Southeast Asian frogs. 100. 60. 80 1. 2. 40. 20. Other Indian/ Southeast Asian frogs. 0. 3. Millions of years ago (mya) 1. 3. 2. India. 100. 60 40 2 3 Millions of years ago (mya). 80 1. 20. 0. Madagascar 88 mya. 56 mya. 65 mya. Fig. 24-7b. 1. 2. 3. India. • Reproductive isolation between populations generally increases as the distance between them increases. Madagascar 88 mya. 65 mya. 56 mya. Degree of reproductive isolation. Fig. 24-8. 2.0. • Barriers to reproduction are intrinsic; separation itself is not a biological barrier. 1.5 1.0 0.5 0 0. 50. 200 250 100 150 Geographic distance (km). 300.
(38) Fig. 24-9. Fig. 24-9a. EXPERIMENT. Initial population. Some flies raised on starch medium. EXPERIMENT Some flies raised on maltose medium. Mating experiments after 40 generations. Initial population. RESULTS Female. 9. 8. 20. Male. 22. Starch Starch population 1 population 2 Starch Starch population 2 population 1. Male Maltose Starch. Female Starch Maltose. Mating frequencies in experimental group. 18. 15. 12. 15. Some flies raised on starch medium. Mating experiments after 40 generations. Some flies raised on maltose medium. Mating frequencies in control group. Fig. 24-9b. RESULTS Female. 9. 8. 20. Starch Starch population 2 population 1. 22. Starch Starch population 1 population 2. Male. Male Maltose Starch. Female Starch Maltose. Mating frequencies in experimental group. 18. 15. 12. 15. Sympatric (“Same Country”) Speciation • In sympatric speciation, speciation takes place in geographically overlapping populations. Mating frequencies in control group. Fig. 24-10-1. Polyploidy • Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division • An autopolyploid is an individual with more than two chromosome sets, derived from one species. 2n = 6. 4n = 12 Failure of cell division after chromosome duplication gives rise to tetraploid tissue..
(39) Fig. 24-10-2. Fig. 24-10-3. 2n = 6. 2n. 4n = 12 Failure of cell division after chromosome duplication gives rise to tetraploid tissue.. 2n = 6. Gametes produced are diploid... 2n. 4n = 12 Failure of cell division after chromosome duplication gives rise to tetraploid tissue.. 4n. Gametes produced are diploid... Offspring with tetraploid karyotypes may be viable and fertile.. Fig. 24-11-1. • An allopolyploid is a species with multiple sets of chromosomes derived from different species. Species B 2n = 4. Unreduced gamete with 4 chromosomes Meiotic error. Normal gamete n=3. Species A 2n = 6. Fig. 24-11-2. Fig. 24-11-3. Species B 2n = 4. Unreduced gamete with 4 chromosomes Meiotic error. Species A 2n = 6. Normal gamete n=3. Species B 2n = 4 Hybrid with 7 chromosomes. Unreduced gamete with 4 chromosomes Meiotic error. Species A 2n = 6. Normal gamete n=3. Hybrid with 7 chromosomes. Unreduced gamete with 7 chromosomes. Normal gamete n=3.
(40) Fig. 24-11-4. Species B 2n = 4. Unreduced gamete with 4 chromosomes Meiotic error. Hybrid with 7 chromosomes. Normal gamete n=3. Species A 2n = 6. • Polyploidy is much more common in plants than in animals • Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids. Unreduced gamete with 7 chromosomes. Normal gamete n=3. Viable fertile hybrid (allopolyploid) 2n = 10. Habitat Differentiation • Sympatric speciation can also result from the appearance of new ecological niches • For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees. Sexual Selection • Sexual selection can drive sympatric speciation • Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria. Fig. 24-12. EXPERIMENT Normal light. P. pundamilia. P. nyererei. Monochromatic orange light. •. Allopatric and Sympatric Speciation: A Review In allopatric speciation, geographic. isolation restricts gene flow between populations • Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations • Even if contact is restored between populations, interbreeding is prevented.
(41) • In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species • Sympatric speciation can result from polyploidy, natural selection, or sexual selection. Patterns Within Hybrid Zones. •. provide opportunities to study factors that cause reproductive A hybrid zoneisolation is a region in which members of different species mate and produce hybrids. Fig. 24-13. EUROPE. Fire-bellied toad range Hybrid zone. Yellow-bellied toad, Bombina variegata. Yellow-bellied toad range. Fire-bellied toad, Bombina bombina. 0.99 Allele frequency (log scale). • A hybrid zone can occur in a single band where adjacent species meet • Hybrids often have reduced fitness compared with parent species • The distribution of hybrid zones can be more complex if parent species are found in multiple habitats within the same region. 0.9. 0.5. 0.1. 0.01 40. Fig. 24-13a. Yellow-bellied toad, Bombina variegata. Fig. 24-13b. Fire-bellied toad, Bombina bombina. 20 30 10 0 10 20 Distance from hybrid zone center (km).
(42) Fig. 24-13c. Hybrid Zones over Time Fire-bellied toad range Hybrid zone. • When closely related species meet in a hybrid zone, there are three possible outcomes:. Allele frequency (log scale). Yellow-bellied toad range 0.99. – Strengthening of reproductive barriers – Weakening of reproductive barriers – Continued formation of hybrid individuals. 0.9 0.5 0.1 0.01 40. 20 10 0 30 20 10 Distance from hybrid zone center (km). Fig. 24-14-1. Fig. 24-14-2. Isolated population diverges. Gene flow Population (five individuals are shown). Gene flow Barrier to gene flow. Population (five individuals are shown). Fig. 24-14-3. Barrier to gene flow. Fig. 24-14-4. Isolated population diverges. Isolated population diverges Hybrid zone. Possible outcomes: Hybrid zone Reinforcement OR Fusion. Gene flow. Gene flow Hybrid. Population (five individuals are shown). Barrier to gene flow. Hybrid Population (five individuals are shown). OR. Barrier to gene flow Stability.
(43) Reinforcement: Strengthening Reproductive Barriers. Fig. 24-15. • The reinforcement of barriers occurs when hybrids are less fit than the parent species • Over time, the rate of hybridization decreases • Where reinforcement occurs, reproductive barriers should be stronger for sympatric than allopatric species. Allopatric male pied flycatcher. Sympatric male pied flycatcher. 28. Pied flycatchers. 24 Number of females. Collared flycatchers 20 16 12 8 4. (none). 0 Females mating Own Other with males from: species species. Own Other species species. Sympatric males. Fig. 24-15a. Allopatric males. Fig. 24-15b. 28. Pied flycatchers. 24 Number of females. Collared flycatchers 20 16 12 8 4 (none). Sympatric male pied flycatcher. 0 Other Females mating Own with males from: species species. Allopatric male pied flycatcher. Sympatric males. Own Other species species Allopatric males. Fig. 24-16. Fusion: Weakening Reproductive Barriers • If hybrids are as fit as parents, there can be substantial gene flow between species • If gene flow is great enough, the parent species can fuse into a single species. Pundamilia nyererei. Pundamilia pundamilia. Pundamilia “turbid water,” hybrid offspring from a location with turbid water.
(44) Stability: Continued Formation of Hybrid Individuals • Extensive gene flow from outside the hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone • In cases where hybrids have increased fitness, local extinctions of parent species within the hybrid zone can prevent the breakdown of reproductive barriers. The Time Course of Speciation • Broad patterns in speciation can be studied using the fossil record, morphological data, or molecular data. Fig. 24-17. long it takes for new species to form, or how many genes need to differ between species. Patterns in the Fossil Record • The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear • Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change • The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence. Speciation Rates. (a) Punctuated pattern. Time. (b) Gradual pattern. •. occur rapidly or slowly and can result from changes in few or Many questions remain concerning how many genes. • The punctuated pattern in the fossil record and evidence from lab studies suggests that speciation can be rapid • The interval between speciation events can range from 4,000 years (some cichlids) to 40,000,000 years (some beetles), with an average of 6,500,000 years.
(45) Fig. 24-18. Fig. 24-18a. (a) The wild sunflower Helianthus anomalus. H. anomalus Chromosome 1 Experimental hybrid H. anomalus Chromosome 2 Experimental hybrid H. anomalus Chromosome 3 Experimental hybrid Key Region diagnostic for parent species H. petiolaris. Region diagnostic for parent species H. annuus. Region lacking information on parental origin. (a) The wild sunflower Helianthus anomalus. (b) The genetic composition of three chromosomes in H. anomalus and in experimental hybrids. Studying the Genetics of Speciation. Fig. 24-18b. H. anomalus Chromosome 1 Experimental hybrid H. anomalus Chromosome 2 Experimental hybrid H. anomalus Chromosome 3 Experimental hybrid. • The explosion of genomics is enabling researchers to identify specific genes involved in some cases of speciation • Depending on the species in question, speciation might require the change of only a single allele or many alleles. Key Region diagnostic for parent species H. petiolaris. Region diagnostic for parent species H. annuus. Region lacking information on parental origin (b) The genetic composition of three chromosomes in H. anomalus and in experimental hybrids. Fig. 24-19. Fig. 24-20. (a) Typical Mimulus lewisii. (b) M. lewisii with an M. cardinalis flower-color allele. (c) Typical Mimulus cardinalis. (d) M. cardinalis with an M. lewisii flower-color allele.
(46) From Speciation to Macroevolution. Fig. 24-UN1. Original population. • Macroevolution is the cumulative effect of many speciation and extinction events. Allopatric speciation. Fig. 24-UN2. Fig. 24-UN3. Ancestral species:. AA Triticum monococcum (2n = 14). Sympatric speciation. BB Wild Triticum (2n = 14). DD Wild T. tauschii (2n = 14). Product:. AA BB DD. T. aestivum (bread wheat) (2n = 42). You should now be able to:. Overview: Lost Worlds. 1. Define and discuss the limitations of the four species concepts 2. Describe and provide examples of prezygotic and postzygotic reproductive barriers 3. Distinguish between and provide examples of allopatric and sympatric speciation 4. Explain how polyploidy can cause reproductive isolation 5. Define the term hybrid zone and d ib th t f h b id. • Past organisms were very different from those now alive • The fossil record shows macroevolutionary changes over large time scales including – The emergence of terrestrial vertebrates – The origin of photosynthesis – Long-term impacts of mass extinctions.
(47) Fig. 25-1. Fig 25-UN1. Cryolophosaurus. Concept 25.1: Conditions on early Earth made the origin of life possible • Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: 1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into macromolecules 3. Packaging of molecules into “protobionts” 4. Origin of self-replicating molecules. • A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a reducing environment • Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible. Synthesis of Organic Compounds on Early Earth • Earth formed about 4.6 billion years ago, along with the rest of the solar system • Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide). • However, the evidence is not yet convincing that the early atmosphere was in fact reducing • Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents Video: Tubeworms Video: Hydrothermal Vent.
(48) Fig. 25-2. • Amino acids have also been found in meteorites. Abiotic Synthesis of Macromolecules • Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock. Protobionts • Replication and metabolism are key properties of life • Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure • Protobionts exhibit simple reproduction and metabolism and maintain an internal chemical environment. Fig. 25-3. • Experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds • For example, small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water. 20 µm. Glucose-phosphate. Glucose-phosphate Phosphatase. Starch Phosphate. (a) Simple reproduction by liposomes. Amylase Maltose. Maltose (b) Simple metabolism.
(49) Fig. 25-3a. Fig. 25-3b. 20 µm. Glucose-phosphate. Glucose-phosphate Phosphatase. Starch Amylase. Phosphate. Maltose. (a) Simple reproduction by liposomes. Maltose (b) Simple metabolism. Self-Replicating RNA and the Dawn of Natural Selection • The first genetic material was probably RNA, not DNA • RNA molecules called ribozymes have been found to catalyze many different reactions – For example, ribozymes can make complementary copies of short stretches of their own sequence or other short pieces of RNA. Concept 25.2: The fossil record documents the history of life • The fossil record reveals changes in the history of life on earth. • Early protobionts with self-replicating, catalytic RNA would have been more effective at using resources and would have increased in number through natural selection • The early genetic material might have formed an “RNA world”. The Fossil Record • Sedimentary rocks are deposited into layers called strata and are the richest source of fossils. Video: Grand Canyon.
(50) Fig. 25-4. Fig. 25-4-1. Rhomaleosaurus victor, a plesiosaur. 100 million years ago. Present. Hallucigenia Casts of ammonites. 200 175. Dimetrodon. 1 cm. 525 500. Hallucigenia. 2.5 cm. 4.5 cm. 565. 4.5 cm. Coccosteus cuspidatus. 400 375. 300 270. Dickinsonia costata. 1 cm. Fossilized stromatolite. 565. Fossilized stromatolite. 3,500 1,500. 600. Stromatolites. 3,500 1,500. 2.5 cm. 525 500. 600. Stromatolites. Dickinsonia costata. Tappania, a unicellular eukaryote. Tappania, a unicellular eukaryote. Fig. 25-4a-2. Rhomaleosaurus victor, a plesiosaur. 100 million years ago. Present. Casts of ammonites. – Existed for a long time – Were abundant and widespread – Had hard parts. How Rocks and Fossils Are Dated • Sedimentary strata reveal the relative ages of fossils • The absolute ages of fossils can be determined by radiometric dating • A “parent” isotope decays to a “daughter” isotope at a constant rate • Each isotope has a known half-life, the time required for half the parent isotope to decay. Animation: The Geologic Record. Fig. 25-5. Fraction of parent isotope remaining. 4.5 cm. Coccosteus cuspidatus. • Few individuals have fossilized, and even fewer have been discovered • The fossil record is biased in favor of species that. 400 375. 300 270. 200 175. Dimetrodon. 1/. 2. Remaining “parent” isotope 1. Accumulating “daughter” isotope 1/. 4 1/. 3 2 Time (half-lives). 8. 1/. 4. 16.
(51) • Radiocarbon dating can be used to date fossils up to 75,000 years old • For older fossils, some isotopes can be used to date sedimentary rock layers above and below the fossil. The Origin of New Groups of Organisms. Fig. 25-6 Synapsid (300 mya). Temporal fenestra. Articular Quadrate. Reptiles (including dinosaurs and birds). Temporal fenestra. Table 25-1. Dimetrodon. Therapsids. Temporal fenestra. EARLY TETRAPODS. Earlier cynodonts. Early cynodont (260 mya). Very late cynodont (195 mya). Archaean, the Proterozoic, and the Phanerozoic eons. Dentary Squamosal. Therapsid (280 mya). Later cynodont (220 mya). p y history include the origins of singlecelled and multicelled organisms the colonization ofinto land • Theand geologic record is divided the. Key. Synapsids. • Mammals belong to the group of animals called tetrapods • The evolution of unique mammalian features through gradual modifications can be traced from ancestral synapsids through the present. • The magnetism of rocks can provide dating information • Reversals of the magnetic poles leave their record on rocks throughout the world. Very late cynodonts. Mammals.
(52) Table 25-1a. Table 25-1b. Fig. 25-7. ic zo leo Pa. • The Phanerozoic encompasses multicellular eukaryotic life • The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic • Major boundaries between geological divisions correspond to extinction events in the fossil record. oM es zoic. Humans. Colonization of land Animals. Origin of solar system and Earth. 4. 1 Proterozoic on so f 2. a ye. Prokaryotes. o ag rs 3. Multicellular eukaryotes. Atmospheric oxygen. Fig 25-UN2. 1. 4. s on lli Bi. 2. of. • The oldest known fossils are stromatolites, rock-like structures composed of many layers of bacteria and sediment • Stromatolites date back 3.5 billion years ago • Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2.1 billion years ago. Archaean. Bil li. Single-celled eukaryotes. The First Single-Celled Organisms. Cenozoic. a s ar ye 3. go. Prokaryotes.
(53) Photosynthesis and the Oxygen Revolution • Most atmospheric oxygen (O2) is of biological origin • O2 produced by oxygenic photosynthesis reacted with dissolved iron and precipitated out to form banded iron formations • The source of O2 was likely bacteria similar to modern cyanobacteria. Fig 25-UN3. • By about 2.7 billion years ago, O2 began accumulating in the atmosphere and rusting iron-rich terrestrial rocks • This “oxygen revolution” from 2.7 to 2.2 billion years ago – Posed a challenge for life – Provided opportunity to gain energy from light – Allowed organisms to exploit new ecosystems. Fig. 25-8. 1. 4. s on lli Bi of. 2. s ar ye 3. o ag. Atmospheric oxygen. The First Eukaryotes. 1. 4. s on lli Bi. 2 Singlecelled eukaryotes. of. • The oldest fossils of eukaryotic cells date back 2.1 billion years • The hypothesis of endosymbiosis proposes that mitochondria and plastids (chloroplasts and related organelles) were formerly small prokaryotes living within larger host cells • An endosymbiont is a cell that lives within a host cell. Fig 25-UN4. ag rs a ye 3. o.
(54) Fig. 25-9-1. • The prokaryotic ancestors of mitochondria and plastids probably gained entry to the host cell as undigested prey or internal parasites • In the process of becoming more interdependent, the host and endosymbionts would have become a single organism • Serial endosymbiosis supposes that mitochondria evolved before plastids through a sequence of endosymbiotic. Fig. 25-9-2. Cytoplasm. Plasma membrane Ancestral prokaryote. DNA. Endoplasmic reticulum. Nucleus. Nuclear envelope. Fig. 25-9-3. Photosynthetic prokaryote Aerobic heterotrophic prokaryote Mitochondrion Mitochondrion Plastid. Ancestral heterotrophic eukaryote. Ancestral photosynthetic eukaryote. Fig. 25-9-4. Plasma membrane. Cytoplasm. Ancestral prokaryote. DNA. Endoplasmic reticulum. Nucleus. Nuclear envelope Aerobic heterotrophic prokaryote. Photosynthetic prokaryote. Mitochondrion Ancestral heterotrophic eukaryote. Mitochondrion Plastid Ancestral photosynthetic eukaryote. • Key evidence supporting an endosymbiotic origin of mitochondria and plastids: – Similarities in inner membrane structures and functions – Division is similar in these organelles and some prokaryotes – These organelles transcribe and translate their own DNA – Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes.
(55) The Earliest Multicellular Eukaryotes. The Origin of Multicellularity • The evolution of eukaryotic cells allowed for a greater range of unicellular forms • A second wave of diversification occurred when multicellularity evolved and gave rise to algae, plants, fungi, and animals. • Comparisons of DNA sequences date the common ancestor of multicellular eukaryotes to 1.5 billion years ago • The oldest known fossils of multicellular eukaryotes are of small algae that lived about 1.2 billion years ago. Fig 25-UN5. • The “snowball Earth” hypothesis suggests that periods of extreme glaciation confined life to the equatorial region or deep-sea vents from 750 to 580 million years ago • The Ediacaran biota were an assemblage of larger and more diverse soft-bodied organisms that lived from 565 to 535 million years ago. of. 2. o ag. s ar ye 3. Multicellular eukaryotes. Fig 25-UN6. Animals. 1. 4. s on lli Bi. • The Cambrian explosion refers to the sudden appearance of fossils resembling modern phyla in the Cambrian period (535 to 525 million years ago) • The Cambrian explosion provides the first evidence of predator-prey interactions. 4. s on lli Bi. The Cambrian Explosion. 1. of. 2. a s ar e y 3. go.
(56) Early Paleozoic era (Cambrian period). Molluscs. Arthropods. Annelids. Chordates. Brachiopods. Sponges. Echinoderms. Millions of years ago. 500. Cnidarians. Fig. 25-10. • DNA analyses suggest that many animal phyla diverged before the Cambrian explosion, perhaps as early as 700 million to 1 billion years ago • Fossils in China provide evidence of modern animal phyla tens of millions of years before the Cambrian explosion • The Chinese fossils suggest that “the Cambrian explosion had a long fuse”. 542. Late Proterozoic eon. Fig. 25-11. The Colonization of Land. (a) Two-cell stage. (b) Later stage. 150 µm. 200 µm. • Fungi, plants, and animals began to colonize land about 500 million years ago • Plants and fungi likely colonized land together by 420 million years ago • Arthropods and tetrapods are the most widespread and diverse land animals • Tetrapods evolved from lobe-finned fishes around 365 million years ago. p dominant groups reflect continental drift, mass extinctions, and adaptive • The history of life onradiations Earth has seen the. Fig 25-UN7. Colonization of land. rise and fall of many groups of organisms. 1. 4. s on lli Bi of. 2. s ar ye 3. o ag Video: Volcanic Eruption Video: Lava Flow.
(57) Continental Drift. Fig. 25-12. • At three points in time, the land masses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago. North American Plate. Crust. Eurasian Plate. Caribbean Plate. Juan de Fuca Plate. Philippine Plate Arabian Plate. Mantle. South American Plate. Pacific Plate. • Earth’s continents move slowly over the underlying hot mantle through the process of continental drift. Indian Plate. Cocos Plate. Nazca Plate. Outer core. African Plate. Inner core. Antarctic Plate. Scotia Plate. (a) Cutaway view of Earth. Australian Plate. (b) Major continental plates. • Oceanic and continental plates can collide, separate, or slide past each other • Interactions between plates cause the formation of mountains and islands and. Fig. 25-12a. Fig. 25-12b. Crust North American Plate Juan de Fuca Plate. Mantle. Eurasian Plate. Caribbean Plate. Philippine Plate Arabian Plate. Indian Plate. Cocos Plate South American Plate. Pacific Plate. Outer core. Nazca Plate. Inner core. (b) Major continental plates. Fig. 25-13. Cenozoic. Present. • Formation of the supercontinent Pangaea about 250 million years ago had many effects. h. Am. ica er. Eurasia Africa India. South America. alia str Au. Madagascar. Antarctica. Millions of years ago. – A reduction in shallow water habitat – A colder and drier climate inland – Changes in climate as continents moved toward and away from the poles – Changes in ocean circulation patterns leading to global cooling. rt No. 65.5. Laurasia. 135. 251. Mesozoic. Consequences of Continental Drift. Antarctic Plate. Scotia Plate. Paleozoic. (a) Cutaway view of Earth. African Plate. Gon dwan. ng Pa. ae. a. a. Australian Plate.
(58) Fig. 25-13a. Fig. 25-13b. Millions of years ago. 65.5. rth No. e Am. a ric. Eurasia Africa. South America. India alia str Au. Gon dwa na. Madagascar. Antarctica. 251. a ae ng Pa. Paleozoic. Cenozoic. Millions of years ago. Present. Mesozoic. Laurasia. 135. Mass Extinctions. • In each of the five mass extinction events, more than 50% of Earth’s species became extinct. Fig. 25-14. 20. 800. 15. 600. 700. 500 10. 400. 5. 200. 300. 100 0. Era Period. E 542. O. Paleozoic S D. 488 444 416. 359. C. Tr. P 299. 251. Mesozoic C J 200. 145. Time (millions of years ago). Cenozoic. P 65.5. N 0. 0. Number of families:. The Big Five Mass Extinction Events. • The fossil record shows that most species that have ever lived are now extinct • At times, the rate of extinction has increased dramatically and caused a mass extinction. Total extinction rate (families per million years):. • The break-up of Pangaea lead to allopatric speciation • The current distribution of fossils reflects the movement of continental drift • For example, the similarity of fossils in parts of South America and Africa is consistent with the idea that these continents were formerly attached.
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