Allopatric speciationMonday, November 9, 20152:59 PM Many species - consist of populations that are spread over wide geographical area - populations look differentRat snakesHuman racesCan we go from that to having different populations becoming different speciesWhat would be requiredDifferent populations of same speciesSomehow become reproductively isolated from each otherHuman races or rat snakesThose aren't reproductively isolatedMembers of all different races - produce fertile offspringGenes flow between populations must be cut off - migrate to other race and interbreedAllopatric peciationPhysical barrier to gene flow occursImagine 2 populations in slightly different geographic areasPhysical barrier that formsPhysically prevents individuals from going from one population to anotherNext part of processIf those two populations isolated from each other - no gene flow between themPersists for a long period of timeEven if barrier dissapears - they won't interbreed

Steps in process - 4 stepsPopulations - spread over geographic areaPopulations become separated by physical barrier for gene flow

Could be riverMountain rangePrevents individuals from moving from one part to another2nd part - barrier must be in place and must be separated for long time - no specific time but fairly longFor step 3 - Genetic differences between populations to emerge and increase4th step if barrier is removed and can come back together - can encounter each other but can't interbreed - have 2 species Example of how this model might work

Indication of range of speciesDifferent colors - winter and summer range- not concerned about thatWestern - western and into central partEastern - eastern part of us but also found towards central partTwo species - ranges are somewhat different but some areas where they overlapThese birds look very similarDifficult to tell apart when looking at themYellow breast with v shapeLook very similarFairly easy to imagine - single ancestral meadowlark speciesSingle species - ranged throughout the united states and north america in generalSomething happened to split range into two - eastern and western populationWhile populations isolated from each otherDifferent - came back together (as they do now)Not capable of breeding with each otherDon't look very different - species recognition can be appearanceSpecies recognition in birds also dependent on songBirds look very similarSongs quite different

Single population could be split Don't know how speciation occursCan put together scenarioNorth america and many part of world - glaciationGlobal temperatures dropped and glaciars moved from north to south

Lobe of glaciar through central iowa and stops right around near des moines isGlaciar itself - physical barrier to animal migrationGlobal cooling - vegetation zones move aroundThings are much colder to norht and species oculd have lived before live farther to southIn this picture - Left vegetation zone - been in existant when vegetationOn right - present vegetation zones

Certain kinds of habitats and vegetationScenario we are developingMeadowlarkDidn't become two different species - more probable some glaciation within 2 million years caused this

Large ice sheet comes down from northPhysical barrierVegetation changes - isolate in different areasSingle population throughout north americaSeparated into eastern and western component due to glacial interferencePopulations remained isolatedBecaome different from each other Human populations with languageIn different areas develop different lnguageEastern vs western songs different - didn't recognize each other Single species spread out over geographical areaBarrier formsPrevents moving from one side to anotherIf removed and populations come back together and resume contactOther possible outcomes too - not just different speciesResume interbreeding - recognize other population and mate and everything goes back to way it wasEngage in limited interbreeding - hybrid zoneIndividuals some of characteristics and other characteristics of other populationOften ask - should we consider the same speciesCan interbreed with and do interbreed in hybrid zone and fertile zoneIn many cases - judgement callWidespread hybrid zoneSingle speciesNarrow - still consider different species

Overlapping ranges in centralHybrid zoneBullocks and baltimoreInterbreed In this areaMaybe we should call them one single speciesCapable of interbreeding

Fairly narrow WidespreadJust keep as 2 separate speciesSympatric speciation can occurAllowpatric - single population into 2 - differences developed because they are separatedSympatric - within population - species in same place - two species form from one in one location Sympatric speciationBird species - within population birds with small beaks and birds with large beaks And birds with beaks in between selected againstContinued selection of that sortSmall beaked and large beaked speciesWe think that sympatric speciation is probably fairly rare but some cases which seem to lend themselves to this expectation

Selection for small beaked and large beaked birds but nothing inbetweenSingle species but could become 2 speciesIf small beak only mated with small beakAnd large beak only mated with large beakSmall beak reproductively isolated from large beak Sympatric speciation did occur in chichlid fishIn africa - large freshwater lake - lake victoria

Lake dried up to nothing and refilled againLast time it refilled - 12 thousand years agoNothing in lake - no fish in thereAll fish there today Established beyond 12 thousand years agoHundreds of species of cichlid fishGotten in lake from someplace else - hard to think thatPretty isolatedHeadwaters of nile riverMore likelyFew species got into this lake and from them all over species came aboutSingle lake - big lake, but single lakeNo physical barriersSeveral things that happened Disruptive selectionWhere and what they feed on and from appearanceVery important in matingAll things combined to produce cichilid fishes in one place Sympatric speciationVery rare for it to occurHowever in plants - much more commonWay it occurs in plants v3ery different from disruptive selection In plants called polyploidyPlants pollen from one plant gets on another plantHybridizing thingsOne of the ways it can occur by polyploidyMating between 2 different plant speciesImagine one of species called a and other we call bRefer to a as whole set of chromosomes and b is whole sset of chromosomes for b

Hybdrid between species a and bOne set of chromosome from a and one set from species bSenario ABProblem with that when ab plant does meiosisChromosomes don't have anything to pair withChromosomes from a don't have something to pair with from b because b is differentThese plants are sterileCan't make viable gametesSpontanous doubling of chromosome numberAb - if chromosomes double now aabbNo problem - can pair withNow fertile - can produce viable gametes and come together and make viable offspringCan't mate back to parent species thoughA parent - it'll produce hybrid aba - mixed up - 3 sets of chromosoemsHave abb - three sets of chromosomes - mismatchNew species - reproductively isolated from parent a and parent bEstimates how common polypoloidy is in plants

Wheat is exampleAgriculture began to develop 10 thousand years agoTaking wild plants and domesticating themSeeds from wild plantsGrowing them in place where you want to grow and harvesting themMany modifications occurWild wheatAt some point - crossed with 2nd species of wild wheat Something people did on purpose or accidentSee corn domesticatedNow unknown species of wild wheat14ab hybrid sterileNot capable of producing gametesThat particular thing - chromosome doubling eventNow has 28 chromosmoes2 representatives of each homologous pairs of chromosomesAnother wheat species developed from combination of 2 speciesFurther infusions of genetic to the point of today common wheat 3 different species genomes all combined

How requent and common one species to split into 2Not know anwer to thatSome situations where it occurs frequentlyAdaptive radiationCases where we are aware of - one linage split into two and other split into more in short period of timeSomething in commonEmpty niches availableNo competition from other speciesAdaptive radiation - on islands Probable of verbs on hawaiin islands - from single bird species - few representatives out to isolated islandsDiversification into many speciesEmpty nichesWhen single bird species got to islandsVery few other birds presentHad run of islands to themselvesEchological niches for birds to occupy but no birds to occupy Empty niches provide a place for them to goAfter extinctions65 million years ago - dinosaurs went extinctEnvironment feedingWhen dinosaurs went extinctMammals capable of diversifying into different echological rolesThird case - see species in new adaptive zone - case where niches not filled because nothing exists to fill itEvolution of flight in birdsAbility to fly around - new world for these organisms - tramendous adaptation after evolution of flight Earliest insects couldn't flyAfter they could - diversified enourmously

Many species - gone extinct but many came from founder speciesBeaks very different from each otherLong beaks - from deep flowersHeavy beaks - eat seedsSmall - eat insectDoing diverse echological thingsDoing diverse echological nichesThose niches empty no tother birds thereAdaptive radiation that produced these speciesGalapagos islands - darwins finchesVery finch like but different beaks - different echological niches

Prior to that time - mammal species around - after line - tremedous species

Idea here - dinosaurs went extinct all niches those dinosaurs occupied vacant and possible for mammal species to move into them and speciation turned led to diversity