BIOL 152 1st Edition Lecture 5Outline of Last Lecture I. Exploring evolutionary processes a. Natural Selectioni. Darwin and Wallace1. Observations generate hypotheses2. Artificial selection as a proxy for natural selectionii. Directional, Disruptive, Stabilizingb. Mating System Influencesi. Sexual selectionsii. Non-random matingc. Immigration/Emigrationd. Population Size/Genetic DrifII. Species and Speciationa. Biodiversityb. Maintaining continuous variationi. Gene flowOutline of Current Lecture I. Speciation and speciesa. IsolationThese 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.i. Prezygoticii. Postzygoticb. Case Study: Rhagoletispomonellai. Life cycleii. Parasites!iii. Hawthorns1. Small fruit2. High nutritional value3. Maggots barely burrow4. High wasp mortality5. Late ripeningiv. Apples1. Large fruit2. Low nutritional value3. Maggots burrow deep4. Low wasp mortality5. Early ripeningv. Types of species1. Biological2. Ecological3. Morphological4. Phylogeneticvi. Types of isolating mechanisms1. Postzygotica. Hybrid inviable or sterile2. Prezygotica. Geographical b. Mechanicalc. Ecological d. Behavioralvii. Types of speciation1. Allopatric2. Sympatric (didn’t get to within lecture)Current LectureMaintaining Continuous Variation- Sympatry- living in the same place - Interbreedingo Gene flow- moving genetic variants within and between populationsMaintaining DIScontinuous variation- Preventing gene flow- Isolationo Prezygotic Preventing fertilizationo Postzygotic Fertilization product inviable or sterile (zygote- first cell in new generation)Isolation » Speciation- Isolated populations accumulate changeso Populations “diverge”o Recognized as “species”A Case Study in SpeciationCrataegus sp. (Hawthorn) trees are native to North America Rhagoletispomonella(Hawthorn maggot fly)- North America native- House fly size- Larvae eat Hawthorn fruitLife Cycle of the maggot fly- Female lays eggs in fruit- Maggots hatch o Feed on fruit- Fruit with maggots drop from treeso Pupation occurs within soil- Adult flies emerge from soilo Fly to treeso Mate on fruit’s surfaceThere are parasites!!- Parasitoid wasp lay eggs in maggot bodieso Paralyzing and killing maggotsHawthorn Features- Native to North America - Small fruitsApple Features- Domesticated apples introduced in the 1600s- Most widely grown fruit- Large compared to Hawthorn fruit- Larvae of rhagoletis started feeding on commercial applesRhagoletishost shif- First noted apple infestation- 1864Are all flies capable of doing this?Apple vs. Hawthorn: A Maggot’s Perspective- Apple is large- 220x more food than Hawthorn- Hawthorn fruit is more nutritiouso Survival rate is higher with HawthornParasite POV- Apples are thicker- more protection- Maggots burrow to avoid wasps- Maggots on apples carry fewer wasp eggsToday:- Hawthorn and Apple maggot flieso Morphologically indistinguishableo BUT genetically distinct- No geographic isolation or physical separation of the two populations- Maggot flies show mating preferences o Hawthorn flies prefer to mate on Hawthorn fruito Apple flies prefer to mate on Apple fruito 4-6% hybridization between populations- Hybrids are viable and fertileo No postzygotic barriers’Timing of host fruit ripening- Leads to temporal separation of the fliesAre the flies separate species?The answer can change with the definition you use of species.Biological Species Definition- Species= a group of interbreeding natural populations whose members can produce viable, fertile offspring and that are reproductively isolated from other such groupsEcological Species Definition- Species= a set of organisms exploiting a single niche. Key aspects of this definition are resources exploited and the habitat occupied by the members of a speciesMorphological Species Definition- Species= a set of individuals with similar morphological features. The key aspect is what the members look like. Individuals of a species are morphologically similar to each other.Phylogenetic Species Definition- Species= a unique lineage or a terminal branch on a phylogenetic tree. Species are defined by their uniquely derived features and shared ancestry.Three Outcomes with renewed or continued contact between two populations:1. Individuals interbreed readily » no speciation2. Individuals do not interbreed » species boundaries enhanced3. Individuals interbreed but offspring have reduced fitness » speciation in progressWhat maintains gene flow barriers?- Postzygotic barriers:o Zygote inviabilityo Hybrid sterility (partial or full) Ex: Horse x donkey= mule (sterile)- Prezygotic barriers o Geographical separation (allopatry)o Mechanical Isolation Ex: Milkweed flower, “Lock and Key” reproduction takes much mechanicalcooperationo Ecological isolation Ex: complexity of a tropical foresto Behavioral isolation Ex: Orchid FlowersHow do species originate?- Natural Selectiono Adaptation to novel habits- Geographic Isolationo Allopatric Speciation “Peripheral isolation” Probably most common speciation pathwayo Proposed by Ernst Mayr- Sympatric speciationo Probably specialized and
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