PLB 115 1st Edition Formation of Species Lecture 20Previous Notes’ OutlineI. EvolutionII. Early Thinking About EvolutionIII. Theory of Natural SelectionIV. The Role of Natural Selection in Evolutiona. UpdateV. Reproductive SuccessVI. Common Misunderstandings About Natural SelectionVII. Importance of Excess ReproductionVIII. Importance of Genetic DiversityIX. Mechanisms that Affect Genetic DiversityX. Differential SurvivalXI. Darwin’s finchesXII. Herbicide-Resistance WeedsXIII. Differential Reproductive RatesXIV. Differential Mate ChoiceXV. Patterns of SelectionXVI. Stabilizing SelectionXVII. Directional SelectionXVIII. Disruptive SelectionCurrent Notes’ OutlineI. Evolutionary Patterns at the Species LevelII. Determining if Two Populations Belong to the Same SpeciesIII. Determining if Two Populations Belong to the Same Species Using Genetic SimilarityIV. How new species originateV. Speciation by Geographic IsolationVI. Mechanisms of Geographic IsolationVII. PolyploidyVIII. Maintaining Reproductive Isolation Between SpeciesIX. Reproductively Isolating MechanismsX. Evolutionary Patterns Above the Species LevelXI. Divergent EvolutionXII. Convergent EvolutionXIII. Homologous and Analogous StructuresThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.XIV. Rates of EvolutionXV. Theories About the Rate of EvolutionXVI. The Tentative Nature of the Evolutionary History of OrganismsXVII. The Origin of Homo Sapiens — Two Points of ViewFormation of SpeciesEvolutionary Patterns at the Species LevelMicroevolution vs. MacroevolutionMicroevolution: Minor differences in allele frequency between populations of the same speciesMacroevolution: Major differences that have occurred over long periods that result in the formation of new speciesSpecies: A group of organisms whose members have the potential to interbreed naturally and produce fertile offspringDetermining if Two Populations Belong to the Same SpeciesGene flow: The movement of genes- Happens from one generation to the next as a result of reproductiono From one region to the next as a result of migrationIf two or more populations exhibit gene flow….- Are considered the same specieso Ex: Horses and donkeys can interbreed, but do not experience gene flow Their offspring (mules) are sterileDetermining if Two Populations Belong to the Same Species Using Genetic Similarity- Organisms belonging to the same species have a high degree of genetic similarity- Similarities in DNA sequences between individuals of two populationso Suggest that gene flow has occurred recently between those populationsEx: Akodon dolores and Akodon molinae- Presumed to be two different species of field mice- Genetic analysis indicated that they were two populations of the same species, living in different geographical regionsHow New Species OriginateSpeciation: The process of generating new species- Speciation has occurred continuously over the history of life on earth- The fossil record shows that huge numbers of new species have originatedo Most of these have gone extinct- There are two main mechanisms of speciationo Geographic isolationo PolyploidySpeciation by Geographic Isolation- Geographic isolation occurs when a portion of a population becomes totally isolated from the resto If it is followed by genetic divergenceo Changes in allele frequencieso Then reproductive isolation can result The isolated population becomes a new speciesMechanisms of Geographic IsolationColonization of a distant areao A few individuals emigrate and establish a population far from their original homeo The distance prohibits gene flow with the original population; the new population becomes reproductively isolatedAppearance of a geographic barrier o Uplifting of mountains, rerouting of rivers, or formation of deserts can subdivide a populationo This barrier prohibits gene flow between the divided subpopulations; they can become reproductively isolatedExtinction of intermediate populationso Occurs when a population that exists between other populations dies out o Eliminates gene flow between the remaining distant populationso The other populations can become reproductively isolated Speciation will only happen if the genetic changes accumulated during the period of reproductive isolation generates two populations that can no longer interbreed and make fertile offspringSpeciation without Geographic Barrierso Any process that leads to reproductive isolation can lead to speciationo May not necessarily require geographic isolationExamples…o Breeding or flowering at different times of yearo Differences in genetically determined courtship and mating behaviorso Genetically determined incompatibility of pollen from one species and flowers of anothero Polyploidy is the primary mechanism of speciation in the absence of geographical isolationPolyploidyo A condition of having multiple sets of chromosomeso More than haploid or diploido Can result from abnormal events in mitosis or meiosiso Chromosomes do not separate properly Cannot mate with its original population Can self-fertilize and generate a new species- Can result from the mating of two different species- The hybrid ends up with a novel number of chromosomes- Cannot mate with either of the parent populationso Ex: Cotton, potato, sugarcane, broccoli, wheat, etc., are all species that resulted from polyploidyMaintaining Reproductive Isolation Between Specieso New species stay reproductively isolated from other species due to mechanisms that prevent mating between speciesReproductively Isolating MechanismsEcological isolating mechanismso Two populations don’t interbreed because they occupy different nichesSeasonal isolating mechanismso Two populations don’t interbreed because they mate at different times of yearBehavioral isolating mechanismso Two populations don’t interbreed because they have different courtship and mating behaviorsMechanical isolating mechanismso Two populations don’t interbreed because they have incompatible genitaliaBiochemical isolating mechanismso Two populations don’t interbreed because their gametes are chemically incompatibleHybrid infertility/in viabilityo Two populations that can interbreed, but their offspring are sterile or die before reproductive maturityEvolutionary Patterns Above the Species Levelo The development of new species is the smallest irreversible unit of