How Populations Evolve Chapter 13 How Populations Evolve

“Nothing in Biology Makes Sense Except in the light of evolution. ” T “Nothing in Biology Makes Sense Except in the light of evolution.” T. Dobzhansky

Clown, Fool, or Simply Well Adapted? Clown, Fool, or Simply Well Adapted? The blue-footed booby Is a type of bird living in the Galápagos Islands

This type of bird possesses many specialized characteristics, called evolutionary adaptations Evolutionary adaptations are inherited traits that enhance its ability to survive and reproduce in its particular environment.

What are some of the characteristics that show evolutionary adaptations for the blue footed booby? The blue-footed booby has: enormous webbed feet an oil producing gland that keeps the booby afloat a nostril that can close under water that prevents water from entering the lungs a gland that secrets salt from consumed sea water and a torpedo-like body All adaptations that make life on the sea feasible.

If you look at any organism critically, you are first struck by the differences from other organisms. Further observations often reveals that an organism’s features show some relationship to where the organism lives and what it does in its environment

DARWIN’S THEORY OF EVOLUTION 13.1 A sea voyage helped Darwin frame his theory of evolution On his visit to the Galápagos Islands: (VIDEO) Charles Darwin observed many unique organisms Iguana Note: Special structures or behaviors help the organism survive and reproduce in a particular environment. Figure 13.1A

Living species have arisen from earlier life forms and that species change over time. Darwin’s main ideas can be traced back to the ancient Greeks. Anaximander (about 2,500 years ago) suggested that life arose in water and that simpler forms preceded more complex forms of life. Aristotle believed that species were fixed and did not evolve. Judeo-Christian tradition that all species were created in a single act of creation about 6,000 years ago.

In the century prior to Darwin In the century prior to Darwin Buffon (mid-1700s) suggested that Earth was much older than 6,000 years, and raised the possibility that different species arose from common ancestors, although he later argued against this point. The study of fossils suggested that life forms change Video Lamarck (early 1800s) was the first to strongly support the idea of evolution, but he believed the mechanism for change was the inheritance of acquired characteristics. He proposed that by using or not using its body parts, an individual may develop certain traits that are passed on to its offspring.

While on the voyage of the HMS Beagle in the 1830s North America Europe Great Britain Africa Equator Asia Australia Tasmania New Zealand PACIFIC OCEAN ATLANTIC OCEAN The Galápagos Islands South America Tierra del Fuego Cape Horn Cape of Good Hope Andes Pinta Marchena Genovesa Santiago Isabela Fernandina Florenza Española San Cristobal Santa Cruz Santa Fe Pinzón Daphne Islands 40 miles 40 km Figure 13.1B While on the voyage of the HMS Beagle in the 1830s Charles Darwin observed similarities between living and fossil organisms and the diversity of life on the Galápagos Islands. Web 13A Darwin and the Galapagos Islands

Darwin’s experiences during the voyage of the Beagle helped him frame his ideas on evolution Species evolve as a result of their interactions with their environment. Darwin was influenced by Lyell’s Principles of Geology, in which he promoted the idea of continual, gradual, and consistent geological change. Darwin coined the term, decent with modification, A unity among organisms related through descent from an ancestor that lived in the remote past. Over millions of years they accumulated diveses adaptations that allowed them to survive.

What was Darwin’s Phrase for evolution? What does it mean? Activity 13B: The Voyage of the Beagle: Darwin's Trip Around the World (13.1)

13.2 Darwin proposed natural selection as the mechanism of evolution 13.2 Darwin proposed natural selection as the mechanism of evolution Darwin observed that organisms Produce more offspring than the environment can support Vary in many characteristics that can be inherited

Darwin reasoned that natural selection Darwin reasoned that natural selection Results in favored traits being represented more and more and unfavored ones less and less in ensuing generations of organisms Darwin observed that species tend to produce excessive numbers of offspring, that the expression of traits varies among the individuals of a population, and that many of these traits are heritable.

What do overproduction of offspring, and heritable variations have to do with organisms becoming adapted to their environment? 1. Every environment has a limited supply of resources. 2. Survival in a limited environment depends in part on the features the organisms inherit from their parents. 3. Those with characteristics favored the environment went on to reproduce 4. Darwin referred to this process as Natural Selection

Hundreds to thousands of years of breeding (artificial selection) Darwin found convincing evidence for his ideas in the results of artificial selection The selective breeding of domesticated plants and animals (modifying species) Figure 13.2A Hundreds to thousands of years of breeding (artificial selection) Ancestral dog (wolf) Figure 13.2B

Thousands to millions of years of natural selection Darwin proposed that living species Are descended from earlier life forms and that natural selection is the mechanism of evolution Hundreds to thousands of years of breeding (artificial selection) Ancestral dog (wolf) Thousands to millions of years of natural selection Ancestral canine African wild dog Coyote Wolf Fox Jackal Figure 13.2C

Two important points can be drawn from Darwin’s theory of natural selection: 1.Ancestral species gave rise to the diverse life forms by transfer of heritable traits to offspring that best promote reproduction. He called this “descent with modification.” 2.Over vast amounts of time, the gradual accumulation of changes in the characteristics among the individuals in a population occurs.

13.3 The study of fossils provides strong evidence for evolution Fossils and the fossil record Strongly support the theory of evolution A Skull of Homo erectus D Dinosaur tracks C Ammonite casts B Petrified tree E Fossilized organic matter of a leaf G “Ice Man” Figure 13.3A–G F Insect in amber

The fossil record Reveals that organisms have evolved in a historical sequence Figure 13.3H

Many fossils link early extinct species with species living today Basilosaurus, an extinct whale whose hind legs link living whales with their land-dwelling ancestors. Figure 13.3I

13.4 A mass of other evidence reinforces the evolutionary view of life. Biogeography Biogeography, the geographic distribution of species Species at different geographical regions are similar to each other This suggested to Darwin that organisms evolve from common ancestors Darwin noted that Galápagos animals Resembled species of the South American mainland more than animals on similar but distant islands

Comparative anatomy Homology Comparative anatomy Is the comparison of body structures in different species Anatomical similarities between many species give signs of common decent. For example, all mammals have the same basic limb structure. Homology Is the similarity in characteristics that result from common ancestry

Homologous structures Homologous structures Are features that often have different functions but are structurally similar because of common ancestry Evolution is a remodeling process. Web activity Vestigial organs Organs that have no know function that are remains from ancestors. Human Cat Whale Bat Figure 13.4A

Comparative Embryology Comparative Embryology Comparative embryology is the comparison of early stages of development among different organisms.

Many vertebrates Have common embryonic structures Pharyngeal pouches Post-anal tail Pharyngeal pouches Chick embryo Human embryo Figure 13.4B Many vertebrates Have common embryonic structures

Molecular Biology Comparisons of DNA and amino acid sequences between different organisms Reveal evolutionary relationships Table 13.4

CONNECTION 13.5 Scientists can observe natural selection in action 13.5 Scientists can observe natural selection in action Camouflage adaptations that evolved in different environments are examples of the results of natural selection. A flower mantid in Malaysia A leaf mantid in Costa Rica Figure 13.5A

Development of pesticide resistance in insects Is another example of natural selection in action These two examples illustrate that natural selection is an editing process, not a creative mechanism. They also show that natural selection is regional, timely, and can occur rapidly. Pesticide application Survivor Chromosome with gene conferring resistance to pesticide Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow Figure 13.5B

In what sense is natural selection more of an editing process than a creative process?

POPULATION GENETICS AND THE MODERN SYNTHESIS 13.6 Populations are the units of evolution Population Is a group of individuals of the same species living in the same place at the same time Species is a group of populations Whose individuals can interbreed and produce fertile offspring A population is the smallest unit that can evolve The increase of resistant insects in areas sprayed with pesticides is a good example of a population evoloving. Natural selection favored genes that were resistant These insects left more offspring The population changed or evolved.

The modern synthesis (1940’s) Population genetics (1920’s) – combined the teachings of Darwin and Mendel Studies how populations change genetically over time The modern synthesis (1940’s) Connects Darwin’s theory with population genetics i.e. populations are the unit of evolution. Key Features of Populations: Populations may be isolated from others of the same species, with little interbreeding and thus little exchange of genes. Islands, mountain ranges

A gene pool Microevolution A gene pool Is the total collection of genes in a population at any one time Alleles in all the individuals within a population. Microevolution Is a change in the relative frequencies of alleles in a gene pool i.e. alleles for pesticide resistance

Why can’t an individual evolve?

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. No matter how many times alleles are shuffled , the frequency of each allele is the gene pool remains the same. Webbing No webbing Figure 13.7A

Hardy-Weinberg equilibrium Hardy-Weinberg equilibrium States that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool Genetic make up of the original population. From the genotype frequency we can calculate the frequency of each allele in this population. Phenotypes Genotypes WW Ww ww Number of animals (total  500) 320 160 20 500 Genotype frequencies  0.64  0.32  0.04 Number of alleles in gene pool (total  1,000) Allele frequencies 800 1,000  0.8 W  0.2 w 640 W 160 W  160 w 40 w Figure 13.7B 200

We can follow alleles in a population To observe if Hardy-Weinberg equilibrium exists P2 + 2pq + q2 = allows us to determine the frequency of genotypes in a gene pool Recombination of alleles from parent generation EGGS Genotype frequencies Allele frequencies 0.64 WW 0.32 Ww 0.04 ww 0.8 W 0.2 w Next generation: W egg p  0.8 w egg q  0.2 W sperm p  0.8 w sperm q  0.2 SPERM WW p2  0.64 Ww pq  0.16 wW qp  0.16 ww q2  0.04 Figure 13.7C

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 These 5 conditions are rarely met. In many populations the rate of evolution is so slow that the population appears close to equilibrium.

Freshman Biology Skip to 13.9 Slide 40

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

13.9 In addition to natural selection, genetic drift and gene flow can contribute to evolution Genetic drift Is a change in the gene pool of a population due to chance The smaller the population the more likely genetic drift will occur. Can alter allele frequencies in a population Genetic drift tend to reduce genetic variation through the loss in alleles

Genetic drift Can cause the bottleneck effect or the founder effect Genetic drift Can cause the bottleneck effect or the founder effect Bottleneck effect is an event that drastically reduces the population Founder effect caused by the colonization of new locations by smaller population. The smaller the group the less likely the genetic makeup will represent the population they left. Original population Bottlenecking event Surviving population Figure 13.9A Figure 13.9B

Gene flow Is the movement of individuals or gametes (pollen grains) between populations Gene flow tends to reduce differences between populations Can alter allele frequencies in a population

Natural selection Leads to differential reproductive success in a population Can alter allele frequencies in a population

List three causes of microevolution List three causes of microevolution. Which one will adapt a population to its environment?

CONNECTION 13.10 Endangered species often have reduced variation 13.10 Endangered species often have reduced variation Low genetic variability May reduce the capacity of endangered species to survive as humans continue to alter the environment Figure 13.10

Skip to 13.18 Natural Selection cannot fashion perfect organisms Slide 59

VARIATION AND NATURAL SELECTION 13.11 Variation is extensive in most populations Many populations exhibit polymorphism Different forms of phenotypic characteristics Figure 13.11

Populations may also exhibit geographic variation Populations may also exhibit geographic variation Variation of an inherited characteristic along a geographic continuum

13.12 Mutation and sexual recombination generate variation 13.12 Mutation and sexual recombination generate variation Mutations, or changes in the nucleotide sequence of DNA Can create new alleles

Sexual recombination Generates variation by shuffling alleles during meiosis A1 A2 A3 and X Parents Meiosis Gametes Fertilization Offspring, with new combinations of alleles Figure 13.12

CONNECTION 13.13 The evolution of antibiotic resistance in bacteria is a serious public health concern The excessive use of antibiotics Is leading to the evolution of antibiotic-resistant bacteria Colorized SEM 5,600 Figure 13.13

13.14 Diploidy and balancing selection variation 13.14 Diploidy and balancing selection variation Diploidy preserves variation By “hiding” recessive alleles Balanced polymorphism May result from the heterozygote advantage or frequency-dependent selection

Some variations may be neutral Some variations may be neutral Providing no apparent advantage or disadvantage Figure 13.14

13.15 The perpetuation of genes defines evolutionary fitness 13.15 The perpetuation of genes defines evolutionary fitness An individual’s fitness Is the contribution it makes to the gene pool of the next generation

13.16 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

Stabilizing selection Directional selection Three possible effects of natural selection Original population Stabilizing selection Evolved population Frequency of individuals Phenotypes (fur color) Directional selection Disruptive selection Figure 13.16

13.17 Sexual selection may produce sexual dimorphism 13.17 Sexual selection may produce sexual dimorphism Sexual selection leads to the evolution of secondary sexual characteristics Which may give individuals an advantage in mating Figure 13.17B Figure 13.17A

13.18 Natural selection cannot fashion perfect organisms 13.18 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