Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 13 How Populations Evolve

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Clown, Fool, or Simply Well Adapted? The blue-footed booby has many specialized characteristics that are very functional in water but less useful on land Such evolutionary adaptations are inherited traits that enhance an organism's ability to survive and reproduce in its particular environment Evolution is the changes in organisms over time

First comes love Then comes baby!

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings DARWIN'S THEORY OF EVOLUTION 13.1 A sea voyage helped Darwin frame his theory of evolution Pre-Darwinian ideas about the origin of species – Early Greek philosophers: Simpler life forms preceded more complex ones – Aristotle: Species are fixed and do not evolve; had a great impact on Western thinking – Judeo-Christian biblical view: All species were individually designed by a divine creator

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In the century prior to Darwin, only a few scientists questioned the belief that species are fixed – Buffon: The study of fossils suggested that Earth is older than 6,000 years, and fossil forms might be early versions of modern forms – Lamarck: Fossils are related to modern forms because life evolves; acquired characteristics are inherited

North America Great Britain ATLANTIC OCEAN PACIFIC OCEAN South America Andes Cape of Good Hope Cape Horn Tierra del Fuego Africa Europe Asia Equator PACIFIC OCEAN Australia Tasmania New Zealand The Galápagos Islands Pinta Fernandina Isabela Santiago Marchena Genovesa Daphne Islands Pinzón Santa Cruz Santa Fe San Cristobal Florenza Española Equator miles 40 km PACIFIC OCEAN Charles Darwin made a round-the-world sea voyage as a naturalist on HMS Beagle in the 1830s

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Darwin observed similarities between living and fossil organisms and the diversity of life on the Galápagos Islands – Darwin's experiences during the voyage helped him frame his ideas about evolution

Frigate bird and giant tortoise

Marine iguana

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lyell's Principles of Geology led him to realize that still-operating natural forces gradually change Earth

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings After his return, Darwin began to document his observations and his new theory of evolution – Alfred Wallace conceived a theory almost identical to Darwin's; both works were presented to the scientific community – Darwin's On the Origin of Species by Means of Natural Selection was published in 1859

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings "Descent with modification" summarizes Darwin's view of life – All organisms are related through descent from a remote common ancestor – Descendants spread into diverse habitats over millions of years and acquired adaptations to their environments – The history of life resembles a tree with multiple branchings from a common trunk – Species that are closely related share characteristics

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 13.2 Darwin proposed natural selection as the mechanism of evolution The essence of Darwin's theory of natural selection is differential success in reproduction – Organisms produce more offspring than the environment can support – Organisms vary in many characteristics that can be inherited – Excessive numbers of organisms lead to a struggle for survival

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Individuals whose characteristics are best adapted to their environment are more likely to survive and reproduce – The unequal ability of individuals to survive and reproduce leads to a gradual change in the characteristics of a population over generations Natural selection is supported by evidence from artificial selection

Controlled Breeding Artificial selection is selective breeding to produce plants and animals that possess desirable traits Modern dogs descended from wolves In only a few thousand years, humans artificially selected for all breeds of modern dogs

LE 13-2c African wild dogCoyoteWolfFoxJackal Thousands to millions of years of natural selection Ancestral canine

Controlled Breeding Humans have created tremendous variation in several species over relatively short periods of time through artificial selection Isn’t it plausible that much larger changes could result from hundreds of millions of years of natural selection?

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 13.3 The study of fossils provides strong evidence for evolution Fossils are the hard parts of organisms that remain after organic materials decay – Rarely, an entire organism is fossilized The fossil record strongly supports the theory of evolution – Changes in sea level and drying and refilling of lakes over time result in rock strata that trap organisms

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Fossils appear in an ordered array within layers of sedimentary rocks – The fossil record reveals that organisms have evolved in a historical sequence Many fossils link early extinct species with species living today

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

13.4 A mass of other evidence reinforces the evolutionary view of life Biogeography – The geographic distribution of species suggested to Darwin that organisms evolve from common ancestors – Isolated organisms resemble each other more than organisms in similar but distant places

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Comparative anatomy – Homologous structures are features that often have different functions but are structurally similar because of common ancestry

LE 13-4a HumanCatWhaleBat

– Vestigial structures are remnants of structures that served important functions in an organism's ancestors

Analogous structures are structures that are outwardly similar in appearance, but differ in their evolutionary origin

Analogous structures result from convergent evolution rather than descent from a common ancestor Convergent evolution occurs when similar environmental pressures and natural selection give rise to similar (analogous) structures in distantly related organisms

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Comparative embryology – Common embryonic structures in all vertebrates are evidence for common descent

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lemur pig human

Embryology All vertebrate embryos possess genes that direct development of gill slits and a tail These genes were inherited from a common ancestor

Embryology Adult fish retain gills and tail because the genes are active throughout their embryonic development Humans are born without gills and a tail because the genes are active only during early embryonic development

LE 13-4b Chick embryo Pharyngeal pouches Post-anal tail Human embryo

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molecular biology – Comparisons of DNA and amino acid sequences between different organisms reveal evolutionary relationships – Molecular biology provides strong evidence that all life forms are related

Molecular biology All organisms share related biochemical processes: –All cells use DNA as genetic blueprint –All use RNA, ribosomes, and approximately the same genetic code for translation –All use roughly the same set of 20 amino acids to build proteins –All use ATP to transfer energy

Molecular biology Striking genetic similarities between organisms imply evolutionary relatedness e.g. the DNA nucleotide sequence of the human and mouse cytochrome c gene is very similar, suggesting shared ancestry

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cytochrome C gene-function in ETC

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 13.5 Scientists can observe natural selection in action Examples of evolutionary adaptation observed over a short time Camouflage Coloration in Trinidadian guppies Pesticide resistance Experimental introductions of Anolis sagrei lizards

Camouflage

Coloration Female guppies prefer to mate with brightly colored males; however, brightly colored males are more likely to be eaten by predators –Males found in areas lacking predators were brightly colored –Males found in areas with predators were duller by comparison (predators eliminated brightly colored males before they could reproduce)

Coloration Conclusion: When fewer predators are present, brighter coloration can evolve Conclusion was confirmed –Predators were introduced to previously predator-free areas (males were brightly colored) –Within a few generations male guppies in those areas evolved to become less colorful

Pesticide Resistance Numerous insect pests have evolved resistance to pesticides –Roaches developed resistance to Combat ®, an insecticide bait that acted as an agent of natural selection –Resistant roaches possessed a rare mutation that caused them to dislike glucose, the main attractant in Combat ®

LE 13-5b Chromosome with gene conferring resistance to pesticide Pesticide application Survivor Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow

Pesticide Resistance At least one insect species is resistant to every pesticide in existence

Experiments Small groups of Anolis sagrei lizards were introduced onto 14 small Bahamian islands with thinly-branched bushes and no trees –Lizards were originally from Staniel Cay, an island with thickly-branched trees –Their long legs were adaptive for maneuvering in these trees The introduced lizards thrived and reproduced

Experiments After 14 years, comparisons were made between lizards on the Bahamian islands and those of Staniel Cay Lizards on all 14 Bahamian islands had shorter, thinner legs

Experiments Conclusion: Individuals with shorter, thinner legs evolved because they were able to escape predators better than their longer-legged ancestors in the new environment

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Examples of evolutionary adaptation reveal three key points about natural selection – Natural selection is more of an editing process than a creative mechanism – Natural selection is contingent on time and place – Significant evolutionary change can occur in a short time

POPULATION GENETICS AND THE MODERN SYNTHESIS 13.6 Populations are the units of evolution – Population A group of individuals of the same species living in the same place at the same time May be isolated from other groups or concentrated The smallest unit that can evolve Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Population genetics – Combines Darwin's and Mendel's ideas in studying how populations change genetically over time – The modern synthesis Connects population genetics with other sciences Focuses on population as the unit of evolution and central role of natural selection

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Studying evolution at the population level – Evolution: change in the prevalence of certain heritable characteristics in a population over a span of generations – Gene pool: the total collection of genes in a population at any one time – Microevolution: a change in the relative frequencies of alleles in a gene pool – Species: a group of populations capable of interbreeding and producing fertile offspring

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 13.7 The gene pool of a nonevolving population remains constant over the generations In a nonevolving population, the shuffling of alleles that accompanies sexual reproduction does not alter the genetic makeup of the population In Hardy-Weinberg equilibrium, the frequency of each allele in the gene pool will remain constant unless acted upon by other agents

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings For a population to be in Hardy-Weinberg equilibrium, it must satisfy five main conditions – The population is very large – The population is isolated – Mutations do not alter the gene pool – Mating is random – All individuals are equal in reproductive success

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Hardy-Weinberg conditions are rarely met in nature – We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists – Hardy-Weinberg equilibrium provides a basis for understanding how populations evolve

LE 13-7a WebbingNo webbing

LE 13-7b Phenotypes Genotypes Number of animals (total = 500) Genotype frequencies Number of alleles in gene pool (total = 1,000) Allele frequencies WW Ww ww W 160 W  160 w 40 w = = = = 0.8 W 800 1,000 = 0.2 w 200 1,000

LE 13-7c Recombination of alleles from parent generation Eggs W egg p = 0.8 w egg q = 0.2 W sperm p = 0.8 w sperm q = 0.2 WW p 2 = 0.64 Ww pq = 0.16 ww q 2 = 0.04 wW qp = 0.16 Next generation: Allele frequencies Genotype frequencies 0.64 WW0.32 Ww0.04 ww 0.8 W0.2 w Sperm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 13.8 The Hardy-Weinberg equation is useful in public health science Public health scientists use the Hardy- Weinberg equation to estimate frequencies of disease-causing alleles in the human population – Example: phenylketonuria (PKU)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 13.9 In addition to natural selection, genetic drift and gene flow can contribute to evolution Genetic drift: change in the gene pool of a population due to chance – Can alter allele frequencies in a population – The smaller the population, the greater the impact Bottleneck effect: an event that drastically reduces population size Founder effect: colonization of a new location by a small number of individuals

LE 13-9a Original population Bottlenecking event Surviving population

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gene flow: the movement of individuals or gametes between populations – Can alter allele frequencies in a population – Tends to reduce differences between populations Natural selection – Best-adapted individuals have the most reproductive success – Results in accumulation of traits that adapt a population to its environment

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION Endangered species often have reduced variation Loss of genetic variability due to bottlenecking may reduce a population's ability to adapt to environmental change – Particularly threatening to endangered species such as the cheetah

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings VARIATION AND NATURAL SELECTION Variation is extensive in most populations Individual variation exists in all sexually reproducing populations Heritable variation results from a combination of genotype and environmental influences – Polymorphism: two or more forms of phenotypic characteristics – Geographic variation: variation of an inherited characteristic from place to place May occur along a geographic continuum (a cline)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mutation and sexual recombination generate variation Mutations-changes in the nucleotide sequence of DNA-can create new alleles – Only mutations in cells that produce gametes can affect a population's gene pool – A mutation may rarely improve adaptation to the environment and thus contribute to evolution Sexual recombination generates variation by shuffling alleles during meiosis

LE 13-12a Parents Meiosis Gametes A1A1 A1A1 A2A2 A3A3  A3A3 A2A2 A1A1

LE 13-12b Fertilization Offspring, with new combinations of alleles and A1A1 A2A2 A1A1 A3A3 A3A3 A2A2 A1A1 Gametes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION The evolution of antibiotic resistance in bacteria is a serious public health concern Natural selection has led to the evolution of antibiotic-resistant bacteria Overuse and misuse of antibiotics has contributed to the proliferation of antibiotic- resistant strains – Example: tuberculosis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diploidy and balancing selection preserve variation Diploidy (two sets of chromosomes) helps to prevent populations from becoming genetically uniform – Recessive alleles are "hidden" from natural selection and remain in the population

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Balancing selection allows two or more phenotypic forms in a population – Balanced polymorphism may result from Heterozygote advantage; example: sickle- cell disease Frequency-dependent selection Neutral variation provides no apparent advantage or disadvantage – Example: fingerprints

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The perpetuation of genes defines evolutionary fitness Evolutionary fitness is the relative contribution an individual makes to the gene pool of the next generation Survival of genes depends on production of fertile offspring Selection indirectly adapts a population to its environment by acting on phenotype

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Natural selection can alter variation in a population in three ways Stabilizing selection: favors intermediate phenotypes Directional selection: acts against individuals at one of the phenotypic extremes Disruptive selection: favors individuals at both extremes of the phenotypic range

LE Original population Evolved population Stabilizing selection Phenotypes (fur color) Original population Frequency of individuals Directional selection Disruptive selection

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sexual selection may produce sexual dimorphism Sexual dimorphism – The distinction in appearance between males and females of a species Sexual selection – The determining of "who mates with whom" – Leads to the evolution of secondary sexual characteristics that may give individuals an advantage in mating

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Natural selection cannot fashion perfect organisms There are at least four reasons why natural selection cannot produce perfection – Organisms are limited by historical constraints – Adaptations are often compromises – Chance and natural selection interact – Selection can only edit existing variations