Chapter 14 The Origin of Species PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
Introduction Many species of cormorants around the world can fly. Cormorants on the Galápagos Islands cannot fly. How did these flightless cormorants get to the Galápagos Islands? Why are these flightless cormorants found nowhere else in the world? 2012 Pearson Education, Inc.
Figure 14.0_1 Chapter 14: Big Ideas Defining Species Mechanisms of Speciation
Figure 14.0_2
Introduction An ancestral cormorant species is thought to have flown from the Americas to the Galápagos Islands more than 3 million years ago. Terrestrial mammals could not make the trip over the wide distance, and no predatory mammals naturally occur on these islands today. Without predators, the environment of these cormorants favored birds with smaller wings, perhaps channeling resources to the production of offspring. 2012 Pearson Education, Inc.
2012 Pearson Education, Inc. DEFINING SPECIES
14.1 The origin of species is the source of biological diversity Microevolution is the change in the gene pool of a population from one generation to the next. Speciation is the process by which one species splits into two or more species. Every time speciation occurs, the diversity of life increases. The many millions of species on Earth have all arisen from an ancestral life form that lived around 3.5 billion years ago. 2012 Pearson Education, Inc.
Figure 14.1
14.2 There are several ways to define a species The word species is from the Latin for kind or appearance. Although the basic idea of species as distinct lifeforms seems intuitive, devising a more formal definition is not easy and raises questions. How similar are members of the same species? What keeps one species distinct from others? 2012 Pearson Education, Inc.
14.2 There are several ways to define a species The biological species concept defines a species as a group of populations, whose members have the potential to interbreed in nature, and produce fertile offspring. Therefore, members of a species are similar because they reproduce with each other. 2012 Pearson Education, Inc.
14.2 There are several ways to define a species Reproductive isolation prevents members of different species from mating with each other, prevents gene flow between species, and maintains separate species. Therefore, species are distinct from each other because they do not share the same gene pool. 2012 Pearson Education, Inc.
Figure 14.2A
Figure 14.2A_1
Figure 14.2A_2
Figure 14.2B
14.2 There are several ways to define a species The biological species concept can be problematic. Some pairs of clearly distinct species occasionally interbreed and produce hybrids. For example, grizzly bears and polar bears may interbreed and produce hybrids called grolar bears. Melting sea ice may bring these two bear species together more frequently and produce more hybrids in the wild. Reproductive isolation cannot usually be determined for extinct organisms known only from fossils. Reproductive isolation does not apply to prokaryotes or other organisms that reproduce only asexually. Therefore, alternate species concepts can be useful. 2012 Pearson Education, Inc.
Figure 14.2C Grizzly bear Polar bear Hybrid grolar bear
Figure 14.2C_1 Grizzly bear
Figure 14.2C_2 Polar bear
Figure 14.2C_3 Hybrid grolar bear
14.2 There are several ways to define a species The morphological species concept classifies organisms based on observable physical traits and can be applied to asexual organisms and fossils. However, there is some subjectivity in deciding which traits to use. 2012 Pearson Education, Inc.
14.2 There are several ways to define a species The ecological species concept defines a species by its ecological role or niche and focuses on unique adaptations to particular roles in a biological community. For example, two species may be similar in appearance but distinguishable based on what they eat or where they live. 2012 Pearson Education, Inc.
14.2 There are several ways to define a species The phylogenetic species concept defines a species as the smallest group of individuals that shares a common ancestor and thus forms one branch of the tree of life. Biologists trace the phylogenetic history of a species by comparing its morphology or DNA. However, defining the amount of difference required to distinguish separate species is a problem. 2012 Pearson Education, Inc.
14.3 Reproductive barriers keep species separate Reproductive barriers serve to isolate the gene pools of species and prevent interbreeding. Depending on whether they function before or after zygotes form, reproductive barriers are categorized as prezygotic or postzygotic. 2012 Pearson Education, Inc.
Figure 14.3A Individuals of different species Prezygotic Barriers Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation Fertilization Postzygotic Barriers Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown Viable, fertile offspring
14.3 Reproductive barriers keep species separate Five types of prezygotic barriers prevent mating or fertilization between species. 1. In habitat isolation, two species live in the same general area but not in the same kind of place. 2. In temporal isolation, two species breed at different times (seasons, times of day, years). Video: Blue-footed Boobies Courtship Ritual Video: Albatross Courtship Ritual Video: Giraffe Courtship Ritual 2012 Pearson Education, Inc.
Figure 14.3B
Figure 14.3B_1
Figure 14.3B_2
Figure 14.3C
Figure 14.3C_1
Figure 14.3C_2
14.3 Reproductive barriers keep species separate Prezygotic Barriers, continued 3. In behavioral isolation, there is little or no mate recognition between females and males of different species. 4. In mechanical isolation, female and male sex organs are not compatible. 5. In gametic isolation, female and male gametes are not compatible. 2012 Pearson Education, Inc.
Figure 14.3D
Figure 14.3E
Figure 14.3F
14.3 Reproductive barriers keep species separate Three types of postzygotic barriers operate after hybrid zygotes have formed. 1. In reduced hybrid viability, most hybrid offspring do not survive. 2. In reduced hybrid fertility, hybrid offspring are vigorous but sterile. 3. In hybrid breakdown, the first-generation hybrids are viable and fertile but the offspring of the hybrids are feeble or sterile. 2012 Pearson Education, Inc.
Figure 14.3G Horse Donkey Mule
Figure 14.3G_1 Horse
Figure 14.3G_2 Donkey
Figure 14.3G_3 Mule
MECHANISMS OF SPECIATION 2012 Pearson Education, Inc.
14.4 In allopatric speciation, geographic isolation leads to speciation In allopatric speciation, populations of the same species are geographically separated, isolating their gene pools. Isolated populations will no longer share changes in allele frequencies caused by natural selection, genetic drift, and/or mutation. 2012 Pearson Education, Inc.
14.4 In allopatric speciation, geographic isolation leads to speciation Gene flow between populations is initially prevented by a geographic barrier. For example the Grand Canyon and Colorado River separate two species of antelope squirrels, and the Isthmus of Panama separates 15 pairs of snapping shrimp. 2012 Pearson Education, Inc.
Figure 14.4A South rim A. harrisii A. leucurus North rim
Figure 14.4A_1 A. harrisii
Figure 14.4A_2 A. leucurus
Figure 14.4B A. formosus A. nuttingi ATLANTIC OCEAN Isthmus of Panama PACIFIC OCEAN A. panamensis A. millsae
14.5 Reproductive barriers can evolve as populations diverge How do reproductive barriers arise? Experiments have demonstrated that reproductive barriers can evolve as a by-product of changes in populations as they adapt to different environments. These studies have included laboratory studies of fruit flies and field studies of monkey flowers and their pollinators. 2012 Pearson Education, Inc.
Figure 14.5A Male Maltose Starch Male Starch medium Initial sample of fruit flies Mating experiments Maltose medium Female Starch Maltose 22 8 20 Results Pop#2 Pop#1 Population #1 Female Population #2 9 18 15 12 15 Number of matings in experimental groups Number of matings in starch control groups
Figure 14.5B Pollinator choice in typical monkey flowers Pollinator choice after color allele transfer Typical M. lewisii (pink) M. lewisii with red-color allele Typical M. cardinalis (red) M. cardinalis with pink-color allele
Figure 14.5B_1 Typical M. lewisii (pink)
Figure 14.5B_2 M. lewisii with red-color allele
Figure 14.5B_3 Typical M. cardinalis (red)
Figure 14.5B_4 M. cardinalis with pink-color allele
14.6 Sympatric speciation takes place without geographic isolation Sympatric speciation occurs when a new species arises within the same geographic area as a parent species. How can reproductive isolation develop when members of sympatric populations remain in contact with each other? Gene flow between populations may be reduced by polyploidy, habitat differentiation, or sexual selection. 2012 Pearson Education, Inc.
14.6 Sympatric speciation takes place without geographic isolation Many plant species have evolved by polyploidy in which cells have more than two complete sets of chromosomes. Sympatric speciation can result from polyploidy within a species (by self-fertilization) or between two species (by hybridization). 2012 Pearson Education, Inc.
Figure 14.6A_s1 1 Parent species 2n = 6 Tetraploid cells 4n = 12
Figure 14.6A_s2 1 2 Parent species 2n = 6 Tetraploid cells 4n = 12 Diploid gametes 2n = 6
Figure 14.6A_s3 1 2 3 Selffertilization Parent species 2n = 6 Tetraploid cells 4n = 12 Diploid gametes 2n = 6 Viable, fertile tetraploid species 4n = 12
Figure 14.6B_s1 Species A 2n = 4 Gamete n = 2 Species B 2n = 6 Gamete n = 3
Figure 14.6B_s2 Chromosomes cannot pair Species A 2n = 4 Gamete n = 2 1 Species B 2n = 6 Gamete n = 3 Sterile hybrid n = 5 Can reproduce asexually 2
Figure 14.6B_s3 Chromosomes cannot pair Species A 2n = 4 Gamete n = 2 1 3 Species B 2n = 6 Gamete n = 3 Sterile hybrid n = 5 Can reproduce asexually 2 Viable, fertile hybrid species 2n = 10
14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation Plant biologists estimate that 80% of all living plant species are descendants of ancestors that formed by polyploid speciation. Hybridization between two species accounts for most of these species. 2012 Pearson Education, Inc.
14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation Polyploid plants include cotton, oats, potatoes, bananas, peanuts, plums, apples, sugarcane, coffee, and bread wheat. barley, 2012 Pearson Education, Inc.
14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation Wheat has been domesticated for at least 10,000 years and is the most widely cultivated plant in the world. Bread wheat, Triticum aestivum, is a polyploid with 42 chromosomes and the result of hybridization and polyploidy. 2012 Pearson Education, Inc.
Figure 14.7_3
Figure 14.7 AA Domesticated Triticum monococcum (14 chromosomes) 1 BB Hybridization Wild Triticum (14 chromosomes) AB Sterile hybrid (14 chromosomes) 2 Cell division error and self-fertilization AABB T. turgidum Emmer wheat (28 chromosomes) DD Wild T. tauschii (14 chromosomes) 3 Hybridization ABD Sterile hybrid (21 chromosomes) 4 Cell division error and self-fertilization AABBDD T. aestivum Bread wheat (42 chromosomes)
Figure 14.7_1 AA Domesticated Triticum monococcum (14 chromosomes) 1 BB Hybridization Wild Triticum (14 chromosomes) AB Sterile hybrid (14 chromosomes) 2 Cell division error and self-fertilization AABB T. turgidum Emmer wheat (28 chromosomes) DD Wild T. tauschii (14 chromosomes)
Figure 14.7_2 AABB T. turgidum Emmer wheat (28 chromosomes) DD 3 Hybridization Wild T. tauschii (14 chromosomes) ABD Sterile hybrid (21 chromosomes) 4 Cell division error and self-fertilization AABBDD T. aestivum Bread wheat (42 chromosomes)
14.8 Isolated islands are often showcases of speciation Most of the species on Earth are thought to have originated by allopatric speciation. Isolated island chains offer some of the best evidence of this type of speciation. Multiple speciation events are more likely to occur in island chains that have physically diverse habitats, islands far enough apart to permit populations to evolve in isolation, and islands close enough to each other to allow occasional dispersions between them. 2012 Pearson Education, Inc.
14.8 Isolated islands are often showcases of speciation The evolution of many diverse species from a common ancestor is adaptive radiation. The Galápagos Archipelago is located about 900 km (560 miles) west of Ecuador, is one of the world s great showcases of adaptive radiation, was formed naked from underwater volcanoes, was colonized gradually from other islands and the South America mainland, and has many species of plants and animals found nowhere else in the world. 2012 Pearson Education, Inc.
14.8 Isolated islands are often showcases of speciation The Galápagos islands currently have 14 species of closely related finches, called Darwin s finches, because Darwin collected them during his aroundthe-world voyage on the Beagle. These finches share many finchlike traits, differ in their feeding habits and their beaks, specialized for what they eat, and arose through adaptive radiation. 2012 Pearson Education, Inc.
Figure 14.8 Cactus-seed-eater (cactus finch) Tool-using insect-eater (woodpecker finch) Seed-eater (medium ground finch)
Figure 14.8_1 Cactus-seed-eater (cactus finch)
Figure 14.8_2 Tool-using insect-eater (woodpecker finch)
Figure 14.8_3 Seed-eater (medium ground finch)
14.9 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin s finches Peter and Rosemary Grant have worked for more than three decades, on medium ground finches, and on tiny, isolated, uninhabited Daphne Major in the Galápagos Islands. 2012 Pearson Education, Inc.
14.9 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin s finches Medium ground finches and cactus finches occasionally interbreed. Hybrids have intermediate bill sizes, survive well during wet years, when there are plenty of soft, small seeds around, are outcompeted by both parental types during dry years, and can introduce more genetic variation on which natural selection acts. 2012 Pearson Education, Inc.
Figure 14.9 Mean beak size Larger Large beaks can crack large seeds Arrival of new species Competitor species, G. magnirostris Severe drought Smaller beaked G. fortis can feed on small seeds Severe drought Smaller 1975 1980 1985 1990 1995 2000 2005 Year
14.10 Hybrid zones provide opportunities to study reproductive isolation What happens when separated populations of closely related species come back into contact with each other? Biologists try to answer such questions by studying hybrid zones, regions in which members of different species meet and mate to produce at least some hybrid offspring. 2012 Pearson Education, Inc.
14.10 Hybrid zones provide opportunities to study reproductive isolation Over time in hybrid zones reinforcement may strengthen barriers to reproduction, such as occurs in flycatchers, or fusion may reverse the speciation process as gene flow between species increases, as may be occurring among the cichlid species in Lake Victoria. In stable hybrid zones, a limited number of hybrid offspring continue to be produced. 2012 Pearson Education, Inc.
Figure 14.10A Three populations of a species 1 2 3 Newly formed species Hybrid zone Population Gene flow Barrier to gene flow 4 Gene flow Hybrid individual
Figure 14.10B Allopatric populations Sympatric populations Male collared flycatcher Male pied flycatcher Pied flycatcher from allopatric population Pied flycatcher from sympatric population
Figure 14.10B_1 Allopatric populations Sympatric populations Male collared flycatcher Male pied flycatcher
Figure 14.10B_2 Pied flycatcher from allopatric population
Figure 14.10B_3 Pied flycatcher from sympatric population
Figure 14.10C Pundamilia nyererei Pundamilia pundamilia Hybrid: Pundamilia turbid water
14.11 Speciation can occur rapidly or slowly There are two models for the tempo of speciation. 1. The punctuated equilibria model draws on the fossil record, where species change most as they arise from an ancestral species and then experience relatively little change for the rest of their existence. 2. Other species appear to have evolved more gradually. Animation: Macroevolution 2012 Pearson Education, Inc.
Figure 14.11 Punctuated pattern Gradual pattern Time
14.11 Speciation can occur rapidly or slowly What is the total length of time between speciation events (between formation of a species and subsequent divergence of that species)? In a survey of 84 groups of plants and animals, the time ranged from 4,000 to 40 million years. Overall, the time between speciation events averaged 6.5 million years. 2012 Pearson Education, Inc.
You should now be able to 1. Distinguish between microevolution and speciation. 2. Compare the definitions, advantages, and disadvantages of the different species concepts. 3. Describe five types of prezygotic barriers and three types of postzygotic barriers that prevent populations of closely related species from interbreeding. 4. Explain how geologic processes can fragment populations and lead to speciation. 2012 Pearson Education, Inc.
You should now be able to 5. Explain how reproductive barriers might evolve in isolated populations of organisms. 6. Explain how sympatric speciation can occur, noting examples in plants and animals. 7. Explain why polyploidy is important to modern agriculture. 8. Explain how modern wheat evolved. 9. Describe the circumstances that led to the adaptive radiation of the Galápagos finches. 2012 Pearson Education, Inc.
You should now be able to 10. Describe the discoveries made by Peter and Rosemary Grant in their work with Galápagos finches. 11. Explain how hybrid zones are useful in the study of reproductive isolation. 12. Compare the gradual model and the punctuated equilibrium model of evolution. 2012 Pearson Education, Inc.
Figure 14.UN01 Zygote Gametes Prezygotic barriers Postzygotic barriers Habitat isolation Reduced hybrid Temporal isolation viability Behavioral isolation Reduced hybrid Mechanical isolation fertility Gametic isolation Hybrid breakdown Viable, fertile offspring
Figure 14.UN02 Original population a. b.
Figure 14.UN03 Species may interbreed in a a. outcome may be b. c. d. when when when reproductive barriers e. are f. are a few hybrids continue to be produced keeps and species separate speciation is reversed
Figure 14.UN03_1 Species may interbreed in a a. outcome may be b. c. d.
Figure 14.UN03_2 b. c. d. when when when reproductive barriers e. are f. are a few hybrids continue to be produced keeps and species separate speciation is reversed
Figure 14.10UN Reinforcement Fusion Stability
Figure 14.10UN_1 Reinforcement
Figure 14.10UN_2 Fusion
Figure 14.10UN_3 Stability