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TAMU BIOL 111 - CPB724_LEC_B1

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Chapter 24Overview: That “Mystery of Mysteries”Concept 24.1: The biological species concept emphasizes reproductive isolationThe Biological Species ConceptSlide 5Reproductive IsolationSlide 7Slide 8Slide 9Slide 10Limitations of the Biological Species ConceptSlide 12Slide 13Allopatric (“Other Country”) SpeciationSlide 15Sympatric (“Same Country”) SpeciationAllopatric and Sympatric Speciation: A SummaryConcept 24.4: Speciation can occur rapidly or slowly and can result from changes in few or many genesPatterns in the Fossil RecordSlide 20Speciation RatesYou should now be able to:PowerPoint Lectures for Biology, Eighth EditionNeil Campbell and Jane ReeceChapter 24Chapter 24The Origin of SpeciesOverview: That “Mystery of Mysteries”•In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth•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 levelConcept 24.1: The biological species concept emphasizes reproductive isolation•Species is a Latin word meaning “kind” or “appearance”•Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms•Speciation, the origin of new species, is at the focal point of evolutionary theoryThe Biological Species Concept•The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; •Gene flow between populations holds the phenotype of a population togetherSimilarity between different species. The eastern meadowlark (Sturnella magna, left) and the western meadowlark (Sturnella neglecta, right) have similar body shapes and colorations. Nevertheless, they are distinct biological species because their songs and other behaviors are different enough to prevent interbreeding should they meet in the wild.(a)Diversity within a species. As diverse as we may be in appearance, all humans belong to a single biological species (Homo sapiens), defined by our capacity to interbreed.(b)Figure 24.3 A, BReproductive Isolation•Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring•Hybrids are the offspring of crosses between different species•Reproductive isolation can be classified by whether factors act before or after fertilization•Prezygotic barriers block fertilization from occurring by:–Impeding different species from attempting to mate–Preventing the successful completion of mating–Hindering fertilization if mating is successful–Habitat, Temporal, Behavioral, Mechanical, and Gametic Isolations Reproductive IsolationPrezygotic barriersHabitat IsolationIndividualsof differentspeciesTemporal IsolationBehavioral IsolationMatingattemptMechanical IsolationGametic IsolationFertilization(a)(b)(d)(c) (e)(f)(g)Prezygotic barriers•Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult:–Reduced hybrid viability–Reduced hybrid fertility–Hybrid breakdownFertilizationReduced Hybrid Viability Reduced Hybrid FertilityPostzygotic barriersHybrid BreakdownViable,fertileoffspring(h)(i)(j)(l)(k)Postzygotic barriersLimitations of the Biological Species Concept•The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes)•Other species concepts emphasize the unity within a species rather than the separateness of different species•The morphological species concept defines a species by structural features–It applies to sexual and asexual species but relies on subjective criteria•The ecological species concept views a species in terms of its ecological niche–It applies to sexual and asexual species and emphasizes the role of disruptive selection•The phylogenetic species concept: defines a species as the smallest group of individuals on a phylogenetic tree–It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species(a) Allopatric speciation. A population forms a new species while geographically isolated from its parent population.(b) Sympatric speciation. A smallpopulation becomes a new specieswithout geographic separation.Figure 24.5 A, B•Concept 24.2: Speciation can take place with or without geographic separation•Speciation can occur in two ways–Allopatric speciation–Sympatric speciationAllopatric (“Other Country”) Speciation•In Allopatric Speciation–Gene flow is interrupted or reduced when a population is divided into two or more geographically isolated subpopulations•Once geographic separation has occurred–One or both populations may undergo evolutionary change during the period of separationFigure 24.6A. harrisiA. leucurus•The magnitude of geographic isolation is a result of the –Type of barrier and the ability of an organism to move about and overcome the barrierAllopatric (“Other Country”) SpeciationSympatric (“Same Country”) Speciation•In Sympatric Speciation–Speciation takes place in geographically overlapping populations–Mechanisms include chromosomal changes and non-random rating (i.e. behavioral changes) that reduces gene flow•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 selectionAllopatric and Sympatric Speciation: A Summary•In allopatric speciation–A new species forms while geographically isolated from its parent population•In sympatric speciation–The emergence of a reproductive barrier isolates a subset of a population without geographic separation from the parent speciesConcept 24.4: Speciation can occur rapidly or slowly and can result from changes in few or many genes •Many questions remain concerning how long it takes for new species to form, or how many genes need to differ between species•Broad patterns in speciation can be studied using the fossil record, morphological data, or molecular dataPatterns in the Fossil Record•The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear•Niles Eldredge and Stephen Jay Gould


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