video slide - Ellen Berwick

Transcript video slide - Ellen Berwick

Chapter 22, 23 and 24

PowerPoint ® Lecture Presentations for

Eighth Edition

Neil Campbell and Jane Reece

A Darwinian View of Life

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

• As the 19th century dawned, it was 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

Lamarck’s Hypothesis of Evolution

• Darwin was not the first to propose a theory explaining the variety of life on earth. • Jean-Babtiste de Lamarck tried to explain how species evolve by hypothesizing through use and disuse of body parts and the inheritance of acquired characteristics • For example, in giraffes, Lamarck’s theory said that their long necks came from stretching to reach leaves on high trees. The more they stretched the longer their neck grew and then their offspring would have longer necks…but we know that things that happen to our bodies during our lifetime are not passed on to our offspring because it doesn’t affect our DNA. If we lose a limb, our children will not all be limbless. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Darwin’s Research

• 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 • His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

GREAT BRITAIN NORTH AMERICA

ATLANTIC OCEAN

The Galápagos Islands

Pinta Genovesa Marchena Santiago Daphne Islands Fernandina Isabela Pinzón Santa Cruz Santa Fe San Cristobal Florenza Española PACIFIC OCEAN

SOUTH AMERICA Cape Horn Tierra del Fuego EUROPE AFRICA Cape of Good Hope

Equator

AUSTRALIA Tasmania New Zealand

Darwin’s Focus on Adaptation

• Darwin had trouble explaining the observations he made about the finches and turtles of the Galapagos simply as “growing” longer beaks or necks. • In reassessing his observations, Darwin perceived

adaptation

to the environment and the origin of new species as closely related processes also now known as natural selection. Nature would “choose” which organisms survive on the basis of their fitness. • 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

(a) Cactus-eater (b) Insect-eater (c) Seed-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

The Origin of Species

• Darwin came to his ideas by a number of observations – – Each species produces more offspring than can survive.

These offspring compete with one another for the limited resources available to them. – – Organisms in every population vary. The offspring with the most favorable traits or variations are the most likely to survive and therefore produce more offspring.

• Darwin developed two main ideas: – Natural selection is a cause of adaptive evolution. 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. – Descent with modification explains life’s unity and diversity. This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Natural Selection

• 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 rise to new species • Note that individuals do not evolve; populations evolve over time • 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

(a) A flower mantid in Malaysia (b) A stick mantid in Africa

Direct Observations of Evolutionary Change

• Two examples provide evidence for natural selection: the effect of differential predation on hummingbird populations and the evolution of drug-resistant HIV Natural Selection of Hummingbirds (Video 4) Put in Video Clip from Darwin’s Dangerous Idea (44:23) •An example of how advanced organs in our bodies evolve from more rudimentary organs. Put in Video Clip from Darwin’s Dangerous Idea (1:03:00) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Types of Selection

• Directional Selection • Stabilizing Selection • Disruptive Selection • Sexual Selection • Artificial Selection

Directional Selection

Stabilizing Selection

Disruptive Selection

Sexual Selection

• •

Sexual selection

is natural selection for mating success It can result in

sexual dimorphism

, marked differences between the sexes in secondary sexual characteristics • • •

Intrasexual selection

is competition among individuals of one sex (often males) for mates of the opposite sex

Intersexual selection

their mates , often called mate choice, occurs when individuals of one sex (usually females) are choosy in selecting Male showiness due to mate choice can increase a male’s chances of attracting a female, while decreasing his chances of survival • • 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

Fig. 23-16 EXPERIMENT SC male gray tree frog SC sperm



Female gray tree frog Eggs



LC sperm LC male gray tree frog Offspring of SC father Offspring of LC father Fitness of these half-sibling offspring compared RESULTS Fitness Measure

Larval growth Larval survival Time to metamorphosis

1995

NSD LC better LC better (shorter)

1996

LC better NSD LC better (shorter) NSD = no significant difference; LC better = offspring of LC males superior to offspring of SC males.

Artificial Selection

• Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called

artificial selection

Cabbage Terminal bud Lateral buds Brussels sprouts Flower clusters Broccoli

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 • In the Darwinian view, the history of life is like a tree with branches representing life’s diversity Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Hyracoidea (Hyraxes) Sirenia (Manatees and relatives)

Moeritherium Barytherium

34 24 Millions of years ago

Deinotherium Mammut Platybelodon Stegodon Mammuthus Elephas maximus

(Asia)

Loxodonta africana

(Africa)

Loxodonta cyclotis

(Africa) 5.5

2 10 4 0 Years ago

Decent with Modification (Video 3)

Evidence of Evolution in Several Areas

• Paleontology- study of the fossil record • Biogeography- study of the distribution of flora (plants) and fauna (animals) in the environment • Embryology- study of the development of an organism • Comparative anatomy- study of the anatomy of various animals and their homologous and analogous structures. • Molecular biology- study of the DNA and chromosomes of organisms.

The Fossil Record

• By dating fossils and examining geologic strata, scientists have been able to put together a time scale for the history of life on earth.

• Fossil evidence indicates that over time organisms of increasing complexity appeared on the earth. Bacteria and blue-green bacteria are the first fossils that were preserved from the Precambrian era. During the beginning of the Paleozoic e ra, complex multicellular invertebrates dominated life in the oceans. By the end of the Paleozoic era, plants and animals has colonized the land surface of the earth. • • The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time.

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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

(a) Pakicetus (terrestrial) (b) Rhodocetus (predominantly aquatic) Pelvis and hind limb (c) Dorudon (fully aquatic) Pelvis and hind limb (d) Balaena (recent whale ancestor)

Biogeography

• • • • Darwin’s observations of

biogeography

, the geographic distribution of species, formed an important part of his theory of evolution • Scientists have found related species in widely separated regions of the world. Islands have many

endemic

species that are often closely related to species on the nearest mainland or island. For example, Darwin observed that animals in the Galapagos have traits similar to those of animals on the mainland of South America. 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.

Embryology

• Comparative embryology reveals anatomical homologies not visible in adult organisms. • If you look at the early stages in vertebrate development, all the embryos look alike. All vertebrates-including fish, amphibians, birds and even humans- show fishlike features called gills slits. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Pharyngeal pouches Chick embryo (LM) Post-anal tail Human embryo

Comparative Anatomy

• • Scientists have discovered that some animals have similar structures that serve different functions. For example, a human’s arm, a cat’s leg, a whale’s fin, and a bat’s wing. •

Humerus

These structures, called

homologous structures,

are features that look similar that represent variations on a structural theme present in a common ancestor. •

Ulna

In contrast, sometimes animals have features with the same function but that are structurally different, such as a bat’s wing and an insect’s wing, which are both used to fly but have evolved independently of each other. These structures are called

analogous structures

Phalanges

Finally, there are

vestigial structures

that are thought to be remnants of features that served important functions in the organism’s ancestors, such as a human’s tail bone.

Bat

Fig. 22-19 Branch point (common ancestor) 1 Tetrapod limbs 2 Amnion 3 Homologous characteristic 4 5 Feathers 6 Lungfishes Amphibians Mammals Lizards and snakes Crocodiles Ostriches Hawks and other birds

Microbiology

• • • • Biochemistry reveals similarities between organisms of different species. For example, the metabolism of vastly different organisms is based on the same complex biochemical compounds. The protein cytochrome c, essential for aerobic respiration, is one such universal compound. The universality of cytochrome c is evidence that all aerobic organisms probably descended from a common ancestor that used this compound for respiration. Further studies of cytochrome c in different species reveal variations in the amino acid sequence of this molecule. For example, the cytochrome c of monkeys and cows is more similar than the cytochrome c of monkeys and fish. Such similarities and differences suggest that monkeys and cows ate more closely related than are monkeys and fish.

Scientists can also examine the nucleotide and amino acid sequences of different organisms’ DNA. From these analyses, we’ve discovered that organisms that are closely related have a greater proportion of sequences in common that distantly related species. Did Humans Evolve? Video 5

Speciation

• Evolution occurs when two organisms undergo natural selection to the point that the two can no longer reproduce to create viable offspring. The endpoint of that particular cycle of evolution is

speciation

or the emergence of a new

species

•

Allopatric speciation

simply means that a population becomes separated from the rest of the species by a geographical barrier so that they can’t interbreed. For example, the squirrels on each side of the Grand Canyon.

•

Sympatric speciation

is when two new species form without any geographic barrier. It is common in plants.

Reproductive Isolation

•

Reproductive isolation

offspring is the existence of biological factors (barriers) that impede two species from producing viable, fertile –

Prezygotic barriers

• • • Impeding different species from attempting to mate – – Preventing the successful completion of mating – Hindering fertilization if mating is successful – block fertilization from occurring by:

Temporal isolation

times of the day, different seasons, or different years cannot mix their gametes

Behavioral isolation

behaviors unique to a species are effective barriers

Mechanical isolation

prevent successful mating

Gametic isolation

: Species that breed at different : Courtship rituals and other : Morphological differences can : Sperm of one species may not be able to fertilize eggs of another species

–

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 fertility: Even if hybrids are vigorous, they may be sterile • Hybrid breakdown Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile

Divergent Evolution

•

Divergent evolution

is the process of two or more related species becoming more and more dissimilar.

• The red fox and the kit fox provide an example of two species that have undergone divergent evolution. The red fox lives in mixed farmlands and forests, where its red color helps it blend in with surrounding trees. The kit fox lives on the plains and in the deserts, where its sandy color helps conceal it from prey and predators. The ears of the kit fox are larger than those of the red fox. The kit fox's large ears are an adaptation to its desert environment. The enlarged surface area of its ears helps the fox get rid of excess body heat. Similarities in structure indicate that the red fox and the kit fox had a common ancestor. As they adapted to different environments, the appearance of the two species diverged.

Convergent Evolution

•

Convergent evolution

is process in which two unrelated and dissimilar species come to have similar, or

analogous

, features often because they have been exposed to similar selective pressures. • For example, sugar glider and flying squirrel; and the giant armadillo, giant pangolin, giant anteater, and spiny anteater • Convergent evolution does not provide information about ancestry Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Sugar glider AUSTRALIA NORTH AMERICA Flying squirrel

Coevolution

• Coevolution is the joint change of two or more species in close interaction. Predators and their prey sometimes coevolve; parasites and their hosts often coevolve; plant-eating animals and the plants upon which they feed also coevolve.

• For example, Newt and Garter Snake Put in The Evolutionary Arms Race video to show example (~3:00)

The Smallest Unit of Evolution

• 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

Population Genetics

• • • • • • Mendel’s laws can also extend to the population level. The

Hardy-Weinberg law

states that even with all the shuffling of genes that goes on, the relative frequencies of genotypes in a population will prevail over time. The alleles don’t get lost in the shuffle. The dominant gene doesn’t become more prevalent, and the recessive gene doesn’t disappear. The frequency of each allele is described in the equation below. Let “p” represent the frequency of the dominant allele and “q” represent the frequency of the recessive allele in the population. The sum of the frequencies must add up to one. p + q = 1 If you know the value of one of the alleles, then you’ll also know the value of the other allele. We can also determine the frequency of the genotypes in a poluation using another equation. p 2 + 2pq + q 2 = 1 where p 2 represents the homozygous dominants, 2pq represents the heterozygotes and q 2 represents the homozygous recessives. For example….

80%

C R

(

= 0.8) 20%

C W

(

= 0.2) Sperm

C R

(80%)

C W

(20%) 64% (

2 )

C R C R

16% (

)

C R C W

16% (

)

C R C W

4% (

2 )

C W C W

64%

C R C R

, 32%

C R C W

, and 4%

C W C W

Gametes of this generation: 64%

C R

+ 16%

C R

= 80%

C R

= 0.8 =

C W

+ 16%

C W

= 20%

C W

= 0.2 =

Genotypes in the next generation: 64%

C R C R

, 32%

C R C W

, and 4%

C W C W

plants

Hardy-Weinberg Equilibrium

• The Hardy-Weinberg law says that a population will be in genetic equilibrium only if it meets these five conditions – A large population – No mutations – No immigration or emigration (gene flow) – Random mating – No natural selection

Violations of the Hardy-Weinberg Law

• Any departure from them results in changes in allele frequencies in a population. • • 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 • Three major factors alter allele frequencies and bring about most evolutionary change: – – – Natural selection (already discussed  ) 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 change from one generation to the next • Genetic drift tends to reduce genetic variation through losses of alleles • Two main examples are known as – The Founder Effect – The Bottlenose Effect

The Founder Effect

• The

founder effect

occurs when a few individuals become isolated from a larger population, such as through migration. • Allele frequencies in the small founder population can be different from those in the larger parent population

The Bottleneck Effect

• 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 • Understanding the bottleneck effect can increase understanding of how human activity affects other species

Original population Bottlenecking event Surviving population

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

• 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

video slide - Ellen Berwick

Transcript video slide - Ellen Berwick

Chapter 22, 23 and 24

A Darwinian View of Life

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