BIOB 272 1st Edition Lecture 29Outline of Last Lecture Sexual Selection Day 2I. Mating Systems and Sexual Selection- Monogamy- Polygyny- Polyandry- Multi-male – Multi-femaleII. Two Categories of Sexual Selection- Male-male competition- Female ChoiceIII. The mammalian baculumIV. Case Study: The Vestigial Whale PelvisV. Female Choice- Why do females make the choices they do?i. Direct Benefits Hypothesisii. Indirect Benefits HypothesisVI. Case Study 2: MT Bison Range Outline of Current Lecture Sexual Selection Day 3/SpeciationI. Case Study- PronghornThese 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. 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 SpeciationCurrent LectureSexual Selection/SpeciationI. Case Study- Pronghorn- Females are very choosy- have complete control over mating- “Attractive” males have more offspring= increase fitness and have higher survival and require fewer resourcesII. Why Females make the Choices that they do- Indirect benefits – Arbitrary Choice Hypothesis: femaleschoose males based on arbitrary traits that indicate theirsons by those males will be more attractive and havegreater access to mates.1. This can lead to runaway divergence if male trait and femalepreference for that trait are genetically correlated(“Fisher’s runaway model”)III. Case Study- Fisher’s Runaway: preference and trait genetically correlated- If father is red- sons will have red and their sons will have red1. Their daughters will prefer males will red2. Heritable and linkage- “Runaway” sexual selection can lead to extreme male traits1. males varytimefemalepreferenceappears2. If offspringinherit bothtrait ANDpreference3. Then positivefeedback loop(assortativemating)IV. Where do Female Preferences Come From- Pre-existing Sensory Biaseso Big, bright, loud things just more obviouso Previous natural selection- Sensory Bias: males exploit pre-existing preferences in femalesV. Sexual Selection- Observationso Variation Existso Variants differ in ability to mate with opposite sexo Variation is inherited2. Outcome: alleles associated with increased mating success will increase in frequency the next generationVI. Species: independently evolving lineagesVII. General Lineage Species Concept:species aremetapopulations that exchange allelesfrequently enough to comprise the same genepoolVIII. Biological Species: groups of actually or potentially interbreeding populations which are reproductively isolated from other such groups- No gene flow- If a population of organisns does not hybridize or interbreed with any other groups, or fails to produce viable or fertile offspring when it does interbreed, it is considered a species1. Problems with biological species concept:o If a group of organisms is divided into 2 groups that could in principle interbreed but in practice never meeto How does one evaluate whether fossils are species?o How does one decide when asexual forms like bacteria are “species”IX. Phylogenetic Species: species are the smallest monophyletic groups - Example: African elephants- Issues: 1. Need a well-resolved phylogeny (many genetic markers)2. Can under-represent diversity- monophyly can take a long time to develop across the entire genomeX. Speciation: once groups have been reproductively isolated for long enough, they should fit the criteria of ALL of the species concepts.- Speciation: the process of genetic divergence leading to complete reproductive isolation- Involves the accumulation of genetic divergence due to barriers to reproductionXI. Speciation Step by Step1. Ancestral Population2. Isolation (often geographic)3. Divergence (evolution of barriers)4. Secondary Contact but no genetic exchangeXII. Allopatric Speciation- Populations in allopatry (“different places”) areseparated by physical barriers to gene flow.- Allopatry is the most common geographical contextfor speciation, but not the only one.- Examples: snapping shrimp at the isthmus of Panamaa. Dispersalb. VicarianceXIII. Ring Species: when isolation accumulates across a species range when gene flow is low or local selection is strong- Continuous distribution but populations at ends can no longer interbreed- Example: Ensatina ring speciesXIV. Sympatric Speciation- Populations in sympatry (“same homeland”) are notseparated by geographic barriers to gene flow.- For sympatric speciation to occur, genetic or ecologicalbarriers to gene flow need to evolve within a singlepopulation- How can sympatric speciation happen?1. Instant genetic barriers- polyploidy speciationo In plants, polyploidy may account for a big fraction (over 10%) of speciation events2. If a single trait causes both disruptive selection and assortative mating, gene flow between different morphs may be low enough that sympatric speciation can