BIOB 272 1st Edition Lecture 30 Outline of Last Lecture Sexual Selection Day 3/SpeciationI. Case Study- PronghornII. Why Females make the Choices that they doIII. Case Study- Fisher’s RunawayIV. Where do Female Preferences Come From- Pre-existing Sensory Biases- Sensory BiasV. Sexual Selection- ObservationsVI. SpeciesVII. General Lineage Species ConceptVIII. Biological SpeciesIX. Phylogenetic SpeciesX. SpeciationXI. Allopatric Speciationa. Dispersalb. VicarianceXII. Ring SpeciesXIII. Sympatric SpeciationOutline of Current Lecture SpeciationI. How Sympatric Speciation Occursa. Instant Genetic Barriersb. If Cause Disruptive Selection and Assortative MatingThese 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.II. Host Shift Example: Hawthorn to AppleIII. Speciation by StepIV. Evolution of Reproductive Barriersa. Types of Reproductive Barriersi. Prezygotic Barrierso Premating:a. Example 1: Sexual Isolation in Firefliesb. Example 2: Mismatched Genital Morphologyo Postmating Barriersii. Postzygotic Barrierso Hybridsa. Example: Horse/Donkeyo How Postzygotic Isolation Evolves- Drosphila ExampleV. Haldane RuleVI. Other Genetic Insights into Postzygotic IsolationVII. Summary of Reproductive BarriersVIII. Secondary ContactIX. When Can Hybrid Zones?a. ReinforcementX. Hybridization Leading to New SpeciesXI. Allopolyploidy Can Lead to Extremely Rapid Hybrid SpeciationXII. Homoploid Hybrid SpeciationXIII. Speciation Key PointsCurrent LectureSpeciationI. How Sympatric Speciation Occursa. Instant Genetic Barriers: Polyploid Speciationo Autopolyploidy: 2n to 4n = one species mating with another oneo Allopolyploidy: 2 species’ genomes combine to make a 3rdo Polyploidy: may account for a big fraction (over 10%) of plants’ speciation eventsb. If Cause Disruptive Selection and Assortative Matingo If a single trait causes both disruptive selection and assortative mating, gene flow between differenct morphs may be low enough that sympatric speciation can occurII. Host Shift Example: Hawthorn to Apple- in Rhagoletis= Ecological Speciationo Apples are relatively new to America- brought here as a cheap source ofsugar to make cheap boozeo Apples created a new host plant for the Rhagoletis to take over= host shifto Ecological Speciation: evolution of reproductive barriers due to adaptation to divergent environmentsIII. Speciation by Stepa. Ancetral Populationb. Isolation (often geographic)c. Divergenced. Secondary Contact but no genetic exchangeIV. Divergence: Evolution of Reproductive Barriers: to be important for speciation, divergence must cause permanent barriers to reproductiona. Types of Reproductive Barrierso Prezygotic Barrierso Premating: sexual or ecological isolationa. Example 1: Sexual Isolation in Fireflies-Females will only mate with males that make appropriate flash patternsb. Example 2: Mismatched Genital Morphologyo Postmating Barriers, Prezygotico Postzygotic Barriers: hybrids formed but are less fit (sterile or inviable)o Hybrids: produced have low fitness-Hybrid inviability, sterility, ecological inviability, behavioral sterilitya. Example: Horse/Donkey:- Postzygotic isolation due to divergence in karyotype- Cross a male donkey (62 chromosomes) with a female horse (64 chromosomes)= mule (63 chromosomes= sterile)o How Postzygotic Isolation Evolves- Drosphila Example- Dobzhansky-Muller Modle for Hybrid Incompatibilities: Fixation can be due to anyevolutionary process. Negative epistatic interactions between interacting pairs of loci (a and b combination is novel and untested by evolution)= Sterile- D-M pairs in Dropohila: some chromosomal combinations cause sterility= large effect of the X. o Patterns From Drosophila Hybrid Sterility: a. Epistasis is a common source of hybrid sterility- also knownin plants, fish and mammalsb. Large effect of X chromosomec. Complete Sterility in male but not female F1sd. All three observation are common in animalsV. Haldane Rule: “When in the offspring of two different animal rfaces one sex is bsent, rare of sterile, that sex is the heterozygous sex.o Points to a central role of the sex chromosomes in speciesVI. Other Genetic Insights into Postzygotic Isolationo Isolation increases with divergenceo Faster evolution of male-specific isolationo Sterility evolves faster than inviabilityo Early stages of isolation are asymmetricVII. Summary of Reproductive Barrierso To be important for speciation, divergence must cause permanent barriers to reproduction o Causes of divergence leading to reproductive barriers o Natural selection o Sexual selection o Genetic drift and bottlenecks (less support) Reproductive isolation is primarily a by-product of evolution by natural or sexual selection within populations, not the direct target of selectionVIII. Secondary Contact: the definitive test of reproductive barriers (but may rarely happen)o Possible Outcomes: Reinforcement or FusionIX. When Can Hybrid Zones Occur?1. Hybrids between incipient species are as fit or more fit than the parents in at least some environments2. Parental Species disperse into the zone and commonly hybridize, but there is selection against hybridsa. Hybrids are less fit due to inviabiltiy or sterilityb. Even if hybrids have lower fitness, hybrid zones can still be conduits for gene flow between species- Hybrid Zones- Cline aHnalysis:o Species boundaries can be semipermeableo Steep clines reflect little gene flow, reproductive barriers - Reinforcement: if hybrids are formed, but have low fitness, selection may favor discriminating individuals (assortative mating)o Postzygotic barriers select for the evolution of prezygotic barrierso Example of reinforcement: genetic distances in 3 Green-eyed tree-frog populations in Australia In zone of secondary contact, hybrid tadpoles fail to develop into frogs= selection to avoid mis-matching Character displacement in body size and songX. Hybridization Leading to New Specieso Forms a third lineage that is independent of the other 2XI. Allopolyploidy Can Lead to Extremely Rapid Hybrid SpeciationXII. Homoploid Hybrid Speciation: rarely, some hybrid gentypes will be better adapted toa novel habitat and can split off as a new species, without a change in ploidyo Example: Helianthus annuus, helianthus petiolaris= helianthus anaomalus (hybrid)XIII. Speciation Key Pointsa. Speciation (for many taxa) is the process of genetic divergence leading to