© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Chapter 14 The Origin of Species

 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? Introduction © 2012 Pearson Education, Inc.

Figure 14.0_1 Defining Species Mechanisms of Speciation Chapter 14: Big Ideas

Figure 14.0_2

 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. Introduction © 2012 Pearson Education, Inc.

DEFINING SPECIES © 2012 Pearson Education, Inc.

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 life- forms 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.

 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 There are several ways to define a species © 2012 Pearson Education, Inc.

 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 There are several ways to define a species © 2012 Pearson Education, Inc.

Figure 14.2A Figure 14.2A Similarity between two species: the eastern meadowlark (left) and western meadowlark (right)

Figure 14.2B

 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 There are several ways to define a species © 2012 Pearson Education, Inc.

Figure 14.2C Grizzly bearPolar bear Hybrid “grolar” bear

 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 There are several ways to define a species © 2012 Pearson Education, Inc.

 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 There are several ways to define a species © 2012 Pearson Education, Inc.

 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 There are several ways to define a species © 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

 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) Reproductive barriers keep species separate © 2012 Pearson Education, Inc.

Figure 14.3B

Figure 14.3B_1

Figure 14.3B_2

Figure 14.3C Figure 14.3C Temporal isolation

Figure 14.3C_1

Figure 14.3C_2

 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 Reproductive barriers keep species separate © 2012 Pearson Education, Inc.

Figure 14.3D Figure 14.3D Behavioral Isolation

Figure 14.3E Figure 14.3E Mechanical isolation

Figure 14.3F Figure 14.3F Gametic isolation

 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 Reproductive barriers keep species separate © 2012 Pearson Education, Inc.

Figure 14.3G Horse Donkey Mule Figure 14.3G Reduced hybrid fertility

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.

 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 In allopatric speciation, geographic isolation leads to speciation © 2012 Pearson Education, Inc.

Figure 14.4A South rim A. harrisii North rim A. leucurus

Figure 14.4B Isthmus of Panama A. millsae A. nuttingi A. formosus A. panamensis ATLANTIC OCEAN PACIFIC OCEAN

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 Starch medium Maltose medium Initial sample of fruit flies Mating experiments Female Results Population #1 Population #2 StarchMaltose Male Maltose Starch Male Pop#2 Pop#1 Number of matings in experimental groups Number of matings in starch control groups

Figure 14.5B Pollinator choice in typical monkey flowers Typical M. lewisii (pink) M. lewisii with red-color allele Typical M. cardinalis (red) M. cardinalis with pink-color allele Pollinator choice after color allele transfer

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.

14.8 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.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 around- the-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)

 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 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin’s finches © 2012 Pearson Education, Inc.

 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 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin’s finches © 2012 Pearson Education, Inc.

Figure 14.9 Larger Smaller Mean beak size Large beaks can crack large seeds Severe drought Year Smaller beaked G. fortis can feed on small seeds Severe drought Competitor species, G. magnirostris Arrival of new species

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.

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.

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. You should now be able to © 2012 Pearson Education, Inc.

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. You should now be able to © 2012 Pearson Education, Inc.

Figure 14.UN01 Zygote Gametes Prezygotic barriers Postzygotic barriers Viable, fertile offspring Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown

Figure 14.UN02 b.a. Original population

Figure 14.UN03 Species may interbreed in a b. c. d. a. outcome may be f. when are when are reproductive barriers when a few hybrids continue to be produced species separate speciation is reversed keeps and e.

Figure 14.UN03_1 Species may interbreed in a b. c. d. a. outcome may be

Figure 14.UN03_2 b. c. d. f. when are when are reproductive barriers when a few hybrids continue to be produced species separate speciation is reversed keepsand e.