SpeciationWhat is EvolutionWhat is EvolutionEvolution is separated into:• anagenesis - evolutionwithin a species lineage —(Darwin’s modification)• cladogenesis - evolutionto form new specieslineages or speciation —(Darwin’s descent)Take a closer look at this process:Generation 2013Generation 2012• in outcrossing diploidorganisms, eachoffspring of the nextgeneration receives acopy of geneticmaterial from twoparents in 2012What is Evolution• who in turn hadreceived their copies ofgenes from two parentsof the precedinggeneration in 2011back in timeAs you go back in time toearlier generations, thegenetic connections appearas a network within thepopulation of interbreedingindividuals1 PopulationWhat is Evolutionback in time• even furtherback in time, thegenetic connections appear asa braided rope within a species• discernible populations ofinterbreeding individuals arerecognized within a species• anagenesis can occur within aspecies lineage through timeWhat is Evolution• as you go back even furtherin time in this tree orphylogeny, the formation ofspecies and the extinction ofspecies (fossils?) are seen• cladogenesis or speciationoccurs when there is completegenetic isolation betweengroups of once connectedpopulationsWhat is Evolutionback in timeWhat is EvolutionSystematics often divided into two areas: phylogenetics or patternand biosystematics or processreticulationtreeWhat is EvolutionSystematics often divided into two areas: phylogenetics or patternand biosystematics or processreticulationtreeIs this a simple dichotomy ofshifting from a reticulatingprocess at or below species levelto a tree pattern above species?What is EvolutionSystematics often divided into two areas: phylogenetics or patternand biosystematics or processreticulationtreeIs this a simple dichotomy ofshifting from a reticulatingprocess at or below species levelto a tree pattern above species?NO!Genes show“tree” patternsin speciesTrees show“reticulation”above speciesGenetic Variation within SpeciesEvolution requires source of genetic variation and a driving forceGenetic variation withinspecies is the rule - humanselection or naturalselection or random eventsinvolvedCapsicum - pepperClaytonia - spring beautyGenetic Variation within SpeciesEvolution requires source of genetic variation and a driving forceClaytonia - spring beautyVariation seen in flowers,pollinators, light regimes,moisture regimes,chromosome numberGenetic Variation within Species• Modern genetic tools indicate substantial genetic variationwithin and among populations of species – raw material fornatural selection or random events to act uponMonotropa hypopithys -pinesapGenetic Variation within SpeciesEvolution requires source of genetic variation and a driving forceClaytonia - spring beautyNatural selection -mechanism by whichpopulations become modifiedin response to theenvironmentAdaptation - adjustment ofthe population to theenvironment• three American botanistsdocumented this linkage with theirstudies on a variety of plant species inCalifornia during 1940-1950sClausen, Hiesey, Keck Genetic Variation within Species• their work on the Achilleamillefolium (yarrow) and Potentillaglandulosa (sticky cinquefoil)complexes are the best knownAchilleaPotentilla• used a reciprocal transplant design by setting up common gardensites across an elevation gradient from coastal California, throughthe Coast Range, and up and over the Sierra NevadaCommon garden at StanfordCommon garden at MatherGenetic Variation within Species• Achillea lanulosa exhibits clinal phenotypic variation innatural populations across the elevational gradient in the SierraNevadaAchillea lanulosaGenetic Variation within SpeciesGenetic Variation within Species• populations exhibit marked lowering of fitness and adaptationwhen placed at other sites — clinal genotypic variation or theformation of ecotypesGenetic Variation within SpeciesEvolution requires source of genetic variation and a driving forceRandom Events - gene frequenciesmay fluctuate despite naturalselection owing to random samplingof genes - genetic drift, founderevents2012orArea “A”2013or dispersal toArea “B”Genetic Variation within SpeciesEvolution requires source of genetic variation and a driving forceRandom Events - gene frequenciesmay fluctuate despite naturalselection owing to random samplingof genes - genetic drift, founderevents• effect is greatest in small,isolated populations on“islands” - e.g., cloud forestpeaks in central PanamaGenetic Variation within SpeciesEvolution requires source of genetic variation and a driving forceRandom Events - gene frequenciesmay fluctuate despite naturalselection owing to random samplingof genes - genetic drift, founderevents• widespread lower elevationLisianthius skinneri (υ) andisolated cloud forest taxa (υ)♦ ♦ ♦ ♦υ υ υ υ υSpeciationCladogenesis - formation of new species• anagenesis - evolutionwithin a species lineage —(Darwin’s modification)• cladogenesis - evolutionto form new specieslineages or speciation —(Darwin’s descent)How to Define Species?Cladogenesis - formation of new speciesHow do you define species?Ernst Mayr• emphasis on reproductive isolatingmechanisms• difficult, due to continuum ofevolutionary processes and productsPlatanus x hybrida - sycamore• common occurrence ofhybrids (even betweengenera) has made the BSCless attractive to botanistsHow to Define Species?• phylogenetic species concepts basedon genealogical separations(reproductive isolation) of groups ofpopulationsHow to Define Species?• others! morphological species,ecological species - all concepts havepros and cons: no universal conceptCeanothus on Catalina Island Reproductive IsolationMany kinds of isolating mechanismsEcological or habitat isolation• species adapted toharsh, heavy metalserpentine soils inCalifornia ecologicalseparated fromcrossing with thosethat do notReproductive IsolationSeasonal or temporal isolation - different times of reproductionReproductive IsolationSeasonal or temporal isolation - different times of reproduction• co-occurrence of many congeners in tropicalforests possible with asynchronous floweringReproductive IsolationMechanical isolation - variation in floral form preventsinterspecies pollen movement• pollen placement or floral formin pseudocopulatory orchids• two western U.S.monkeyflowers Mimuluscardinalis and M. lewisii — apair of recently speciatedspecies — are