Chapter 24 The Origin of Species Power Point

Chapter 24 The Origin of Species Power. Point Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

Figure 14. 0_1 Chapter 14: Big Ideas Defining Species Mechanisms of Speciation

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_2

Figure 14. 1

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.

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. 2 A Eastern Meadowlark Western Meadowlark

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. 2 C Grizzly bear Polar bear Hybrid “grolar” bear

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.

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.

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.

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. 3 A 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: Giraffe Courtship Ritual © 2012 Pearson Education, Inc.

Figure 14. 3 B Habitat Isolation 2 species of garter snakes Thamnophis A lives in mainly in water B lives on land

Figure 14. 3 C Temporal Isolation Eastern spotted skunk – breeds in late winter Western spotted skunk – breeds in the fall.

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 ex. Courtship rituals in birds 4. In mechanical isolation, female and male sex organs are not compatible. Ex. Insects have unique and complex males structures that will fit in female structures of the same species, snails that have spirals in different directions prevent from genital openings to align. 5. In gametic isolation, female and male gametes are not compatible. Ex. Pollen of same species will allow fertilization, release of sperm in water in aquatic species. © 2012 Pearson Education, Inc.

Figure 14. 3 E Genital openings (black and white arrows) not aligned

Figure 14. 3 F

Reproductive barriers keep species separate § Postzygotic barriers operate after hybrid zygotes have formed. Chromosome incompatibility, 3 types 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. 3 G Horse Donkey Mule

MECHANISMS OF SPECIATION © 2012 Pearson Education, Inc.

In allopatric speciation, geographic isolation leads to speciation § In allopatric speciation, populations of the same species are geographically separated, isolating their gene pools. – the Grand Canyon and Colorado River separate two species of antelope squirrels, and – the Isthmus of Panama separates 15 pairs of snapping shrimp. § Isolated populations will no longer share changes in allele frequencies caused by – natural selection, – genetic drift, and/or – mutation. © 2012 Pearson Education, Inc.

Figure 14. 4 A North rim South rim A. harrisii A. leucurus

Figure 14. 4 B A. formosus A. nuttingi ATLANTIC OCEAN Isthmus of Panama PACIFIC OCEAN A. panamensis A. millsae

Figure 14. 5 B 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

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? Gene flow between populations may be reduced by – polyploidy, – habitat differentiation, or – sexual selection. © 2012 Pearson Education, Inc.

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 (cells containing more than 2 N chromosomes when sister chromatids or homologous chromosomes don’t separate during meiosis) and fertilization – within a species (by self-fertilization) or – between two species (by hybridization). © 2012 Pearson Education, Inc.

Figure 14. 6 A_s 3 1 2 Parent species 2 n = 6 3 Selffertilization Tetraploid cells 4 n = 12 Diploid gametes 2 n = 6 Viable, fertile tetraploid species 4 n = 12

Figure 14. 6 B_s 1 Species A 2 n = 4 Species B 2 n = 6 Gamete n=2 Gamete n=3

Figure 14. 6 B_s 2 Chromosomes cannot pair Species A 2 n = 4 Gamete n=2 1 Sterile hybrid n=5 Species B 2 n = 6 Gamete n=3 Can reproduce asexually 2

Figure 14. 6 B_s 3 Chromosomes cannot pair Species A 2 n = 4 Gamete n=2 3 1 Sterile hybrid n=5 Species B 2 n = 6 Gamete n=3 Can reproduce asexually Viable, fertile hybrid species 2 n = 10 2 Errors in cell division

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.

EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation § Polyploid plants include – cotton, – plums, – oats, – apples, – potatoes, – sugarcane, – bananas, – coffee, and – peanuts, – 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 AA BB Wild Triticum (14 chromosomes) Domesticated Triticum monococcum (14 chromosomes) 1 Hybridization AB Sterile hybrid (14 chromosomes) 2 Cell division error and self-fertilization DD AABB T. turgidum Emmer wheat (28 chromosomes) 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)

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.

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.

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)

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.

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 Large beaks can crack large seeds Competitor species, G. magnirostris Mean beak size Larger Arrival of new species Smaller beaked G. fortis can feed on small seeds Severe drought Smaller 1975 1980 1985 1990 Year 1995 2000 2005

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. 10 A Newly formed species Three populations of a species 3 Hybrid zone 2 1 4 Gene flow Population Barrier to gene flow Hybrid individual

Figure 14. 10 B Allopatric populations Sympatric populations Male collared flycatcher Male pied flycatcher Pied flycatcher from allopatric population Pied flycatcher from sympatric population

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

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. UN 01 Zygote Gametes Prezygotic barriers • Habitat isolation • Temporal isolation • Behavioral isolation • Mechanical isolation • Gametic isolation Postzygotic barriers • Reduced hybrid viability • Reduced hybrid fertility • Hybrid breakdown Viable, fertile offspring

Figure 14. UN 02 Original population a. b.

Figure 14. UN 03 Species may interbreed in a a. outcome may be b. c. when d. when are a few hybrids continue to be produced reproductive barriers are f. e. keeps species separate and speciation is reversed

Figure 14. UN 03_1 Species may interbreed in a a. outcome may be b. c. d.

Figure 14. UN 03_2 b. c. when d. when are a few hybrids continue to be produced reproductive barriers are f. e. keeps species separate and speciation is reversed