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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 Video: Galápagos Tortoise Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Speciation, the origin of new species, is at the focal point of evolutionary theory • 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 Animation: Macroevolution The Biological Species Concept • Members of a biological species are reproductively compatible, at least potentially; they cannot interbreed with other populations. Similarity between different species. Diversity within a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 – 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 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 • Behavioral isolation: Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Mechanical isolation: Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Gametic isolation: Video: Albatross Courtship Ritual Video: Blue-footed Boobies Courtship Ritual Video: Giraffe Courtship Ritual 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 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 • 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 • Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Hybrid breakdown: when hybrids mate with either parent species, offspring of the next generation are feeble or sterile 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 Allopatric (“Other Country”) Speciation • In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations A. harrisi Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A. leucurus 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 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4n 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 P. pundamilia Normal light P. nyererei Monochromatic orange light 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 The Hawaiian archipelago is one of the world’s great showcases of adaptive radiation Dubautia laxa KAUAI 5.1 million years 1.3 million MOLOKAI years MAUI OAHU 3.7 LANAI million years Argyroxiphium sandwicense HAWAII 0.4 million years Dubautia waialealae Dubautia scabra Dubautia linearis The Tempo of Speciation • 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 Pigmented cells (photoreceptors) Pigmented cells Epithelium Nerve fibers Patch of pigmented cells Some complex structures, such as the eye, have had similar functions during all stages of their evolution 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 Animation: Allometric Growth 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 Chimpanzee fetus Chimpanzee adult Human fetus Human adult Comparison of chimpanzee and human skull growth Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-16 Heterochrony has also played a part in the evolution of salamander feet 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 Changes in Spatial Pattern • Homeotic genes determine such basic features as where wings and legs will develop on a bird or how a flower’s parts are arranged – 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 Hox Genes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 24-18 Chicken leg bud Region of Hox gene expression Zebrafish fin bud