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Chapter 24 The Origin of Species PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: The “Mystery of Mysteries” • In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Speciation, the origin of new species, is at the focal point of evolutionary theory • Evolutionary theory must explain how new species originate and how populations evolve • Microevolution consists of adaptations that evolve within a population, confined to one gene pool • Macroevolution refers to evolutionary change above the species level Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Two basic patterns of evolutionary change: – Anagenesis (phyletic evolution) transforms one species into another – Cladogenesis (branching evolution) is the splitting of a gene pool, giving rise to one or more new species Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-2 Anagenesis Cladogenesis Concept 24.1: The biological species concept emphasizes reproductive isolation • Species is a Latin word meaning “kind” or “appearance” Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Biological Species Concept • Members of a biological species are reproductively compatible, at least potentially; they cannot interbreed with other populations. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-3 Similarity between different species. Diversity within a species. Reproductive Isolation • Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile hybrids • Two types of barriers: prezygotic and postzygotic Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Prezygotic barriers impede mating or hinder fertilization if mating does occur: – Habitat isolation – Temporal isolation – Behavioral isolation – Mechanical isolation – Gametic isolation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-4a Prezygotic barriers impede mating or hinder fertilization if mating does occur Habitat isolation Temporal isolation Behavioral isolation Individuals of different species Mechanical isolation Gametic isolation Mating attempt HABITAT ISOLATION Fertilization TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION GAMETIC ISOLATION Postzygotic barriers prevent a hybrid zygote from developing into a viable, fertile adult Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown Viable, fertile offspring Fertilization REDUCED HYBRID VIABILITY REDUCED HYBRID FERTILITY HYBRID BREAKDOWN • Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Mechanical isolation: Morphological differences can prevent successful mating Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-4aa Prezygotic barriers impede mating or hinder fertilization if mating does occur Habitat isolation Individuals of different species HABITAT ISOLATION Temporal isolation Behavioral isolation Mechanical isolation Mating attempt TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION Gametic isolation Fertilization GAMETIC ISOLATION • Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: – Reduced hybrid viability – Reduced hybrid fertility – Hybrid breakdown Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Reduced hybrid viability: Genes of the different parent species may interact and impair the hybrid’s development Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-4ab Postzygotic barriers prevent a hybrid zygote from developing into a viable, fertile adult Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown Viable, fertile offspring Fertilization REDUCED HYBRID VIABILITY REDUCED HYBRID FERTILITY HYBRID BREAKDOWN Limitations of the Biological Species Concept • The biological species concept does not apply to – Asexual organisms – Fossils – Organisms about which little is known regarding their reproduction Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other Definitions of Species • Morphological: defines a species by structural features • Paleontological: focuses on morphologically discrete species known only from the fossil record • Ecological: views a species in terms of its ecological niche • Phylogenetic: defines a species as a set of organisms with a unique genetic history Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 24.2: Speciation can take place with or without geographic separation • Speciation can occur in two ways: – Allopatric speciation – Sympatric speciation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-5 Allopatric speciation Sympatric speciation Allopatric (“Other Country”) Speciation • In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations • One or both populations may undergo evolutionary change during the period of separation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-6 A. harrisi A. leucurus • To determine if allopatric speciation has occurred, reproductive isolation must have been established Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-7a Initial population of fruit flies (Drosophila pseudoobscura) Some flies raised on starch medium Mating experiments after several generations Some flies raised on maltose medium LE 24-7b 22 9 8 20 Mating frequencies in experimental group Male Same Different populations population Male Maltose Starch Female Starch Maltose Female Different Same population populations 18 15 12 15 Mating frequencies in control group Sympatric (“Same Country”) Speciation • In sympatric speciation, speciation takes place in geographically overlapping populations Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Polyploidy • Polyploidy is presence of extra sets of chromosomes due to accidents during cell division • It has caused the evolution of some plant species • An autopolyploid is an individual with more than two chromosome sets, derived from one species Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-8 Failure of cell division in a cell of a growing diploid plant after chromosome duplication gives rise to a tetraploid branch or other tissue. 2n = 6 Gametes produced by flowers on this tetraploid branch are diploid. Offspring with tetraploid karyotypes may be viable and fertile— a new biological species. 2n 4n = 12 4n • An allopolyploid is a species with multiple sets of chromosomes derived from different species Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-9 Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes Unreduced gamete with 7 chromosomes Viable fertile hybrid (allopolyploid) Meiotic error; Species A chromosome number not 2n = 4 reduced from 2n to n 2n = 10 Normal gamete n=3 Species B 2n = 6 Normal gamete n=3 Habitat Differentiation and Sexual Selection • Sympatric speciation can also result from the appearance of new ecological niches • In cichlid fish, sympatric speciation has resulted from nonrandom mating due to sexual selection Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-10 P. pundamilia P. nyererei Normal light Monochromatic orange light Allopatric and Sympatric Speciation: A Summary • In allopatric speciation, a new species forms while geographically isolated from its parent population • In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Adaptive Radiation • Adaptive radiation is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The Hawaiian archipelago is one of the world’s great showcases of adaptive radiation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-12 Dubautia laxa KAUAI 5.1 million years 1.3 million years MOLOKAI MAUI OAHU 3.7 LANAI million years Argyroxiphium sandwicense HAWAII 0.4 million years Dubautia waialealae Dubautia scabra Dubautia linearis Studying the Genetics of Speciation • The explosion of genomics is enabling researchers to identify specific genes involved in some cases of speciation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Tempo of Speciation • The fossil record includes many episodes in which new species appear suddenly in a geologic stratum, persist essentially unchanged through several strata, and then apparently disappear • Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change • The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-13 Time Gradualism model Punctuated equilibrium model Concept 24.3: Macroevolutionary changes can accumulate through many speciation events • Macroevolutionary change is cumulative change during thousands of small speciation episodes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolutionary Novelties • Most novel biological structures evolve in many stages from previously existing structures Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Some complex structures, such as the eye, have had similar functions during all stages of their evolution Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-14 Pigmented cells (photoreceptors) Pigmented cells Epithelium Nerve fibers Patch of pigmented cells Fluid-filled cavity Epithelium Optic nerve Nerve fibers Eyecup Cellular fluid (lens) Pigmented layer (retina) Pinhole camera-type eye Optic nerve Eye with primitive lens Cornea Lens Retina Optic nerve Complex camera-type eye Cornea Evolution of the Genes That Control Development • Genes that program development control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Changes in Rate and Timing • Heterochrony is an evolutionary change in the rate or timing of developmental events • It can have a significant impact on body shape • Allometric growth is the proportioning that helps give a body its specific form Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-15a Newborn 2 15 5 Age (years) Differential growth rates in a human Adult • Different allometric patterns contribute to the contrasting shapes of human and chimpanzee skulls Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-15b Chimpanzee fetus Chimpanzee adult Human adult Human fetus Comparison of chimpanzee and human skull growth • Heterochrony has also played a part in the evolution of salamander feet Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-16 Ground-dwelling salamander Tree-dwelling salamander • In paedomorphosis, the rate of reproductive development accelerates compared with somatic development • The sexually mature species may retain body features that were juvenile structures in an ancestral species Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Changes in Spatial Pattern • Substantial evolutionary change can also result from alterations in genes that control the placement and organization of body parts • Homeotic genes determine such basic features as where wings and legs will develop on a bird or how a flower’s parts are arranged Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The products of one class of homeotic genes called Hox genes • Hox genes provide positional information in the development of fins in fish and limbs in tetrapods Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-18 Chicken leg bud Region of Hox gene expression Zebrafish fin bud • Evolution of vertebrates from invertebrate animals was associated with alterations in Hox genes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-19 Hypothetical vertebrate ancestor (invertebrate) with a single Hox cluster First Hox duplication Hypothetical early vertebrates (jawless) with two Hox clusters Second Hox duplication Vertebrates (with jaws) with four Hox clusters Evolution Is Not Goal Oriented • The fossil record often shows apparent trends in evolution that may arise because of adaptation to a changing environment Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-20 Recent Equus Hippidion and other genera Pleistocene Nannippus Pliohippus Hipparion Neohipparion Pliocene Sinohippus Megahippus Callippus Archaeohippus Merychippus Miocene Anchitherium Hypohippus Parahippus Miohippus Oligocene Mesohippus Paleotherium Epihippus Propalaeotherium Eocene Pachynolophus Orohippus Key Hyracotherium Grazers Browsers • According to the species selection model, trends may result when species with certain characteristics endure longer and speciate more often than those with other characteristics • The appearance of an evolutionary trend does not imply that there is some intrinsic drive toward a particular phenotype Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings