Outline of Last LectureOutline of Current LectureSpeciationSpeciesDistinguishing SpeciesHow do Species form?AllopatricSecondary ContactSympatricPolyploidyReviewBio Sci 150 1st Edition Lecture 16Outline of Last Lecture 1. Evolution a. Review2. Natural Selectiona. Directional selection b. Stabilizing selection c. Disruptive/Diversifying selection d. Balancing selection 3. Sexual Selectiona. Male vs. FemaleOutline of Current Lecture 1. Speciationa. Speciesi. Distinguishing Species1. The Biological Species Concept2. The Phylogenetic Species Conceptii. How Species Form1. Allopatric a. Colonization eventsb. Vicariance eventc. Adaptive radiationd. Secondary Contact2. Sympatrica. PolyploidyCurrent LectureKey TermsSpeciation: the origin of new speciesIsolation: created by reductions in gene flow.Divergence: created when mutation, genetic drift, and selection act on populationsSpecies: distinct types of organisms that represent evolutionarily independent groups.These 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.The Biological Species Concept: Individuals of different species cannot interbreed, and their populations are considered reproductively isolatedThe Phylogenetic Species Concept: the smallest set of organisms that share an ancestor and can be distinguished from other such sets.Phylogeny: the evolutionary history of a group of organisms Phylogenetic tree: a branching diagram that depicts the evolutionary relationships between organismsMonophyletic group (one- tribe): An ancestral species and all of its descendants (= branch, lineage or clade)Allopatric: Geographic barrier blocks gene flowSympatric: Intrinsic barrier blocks gene flowColonization events: a species spreads to new areas Vicariance event: a physical barrier separates a populationAdaptive radiation: evolution of many species from a common ancestorSecondary Contact: Mechanisms that can prevent gene flow when reproductively isolated species come back in contact with each other following isolation and divergencePrezygotic mechanisms make it very unlikely that interbreeding will even take placePostzygotic mechanisms cause hybrids to become sterile or to fail to develop properly.Polyploidy, a type of mutation, where more than 2n chromosomes are presentTetraploid (4n chromosome number)SpeciationDefinition: the origin of new species- A splitting event that creates two or more distinct species from a single ancestral group. - Speciation is the outcome of isolation and divergenceo Isolation is created by reductions in gene flow.o Divergence is created when mutation, genetic drift, and selection act on populationsSpeciesDefinition: distinct types of organisms that represent evolutionarily independent groups.- Lack of gene flow makes a species independent. - "Species" are a way we classify continuous evolutionary variation into discrete categories - Originally organisms that looked different were considered separate specieso ...But some species that look similar are really differento ...And some that look different are actually the same specieso ...More that look different and are the same species (sometimes)Distinguishing SpeciesTwo criteria for distinguishing species1. The Biological Species Concepta. Species: individuals that interbreed (or have the potential to interbreed) in natural environments b. Individuals of different species cannot interbreed, and their populations are considered reproductively isolatedc. Problem: Cannot evaluate reproductive isolation in fossil or asexual species2. The Phylogenetic Species Concepta. Definition: the smallest set of organisms that share an ancestor and can be distinguished from other such sets.b. Phylogeny: the evolutionary history of a group of organisms c. Phylogenetic tree: a branching diagram that depicts the evolutionary relationships between organismsi. Example: Darwin's "tree of life" (1859)d. Monophyletic group (one- tribe): An ancestral species and all of its descendants (= branch, lineage or clade)i. Species: the smallest monophyletic group in a tree that compares populations (A's = bluebirds; F's = Am. Robin) ii. Can also describe higher level groups (e.g., "Robins")iii. Contain all the descendants of a common ancestore. Advantagesi. Widely applicableii. Based on evolution (phylogenetic relationships)f. Disadvantage - Few phylogenies available3. Species concepts in action:a. Endangered Species Act is based on the Biological Species Concept. b. It recognizes “subspecies” for vertebratesHow do Species form?AKA - Modes of Speciation (both based on interruption of gene flow)Allopatric- Geographic barrier blocks gene flow- Ranges do not overlap- Four Kinds…1. Colonization events are more common on islands. 2. When a physical barrier separates a population, a vicariance event is said to occur3. Adaptive radiation - evolution of many species from a common ancestor4. Secondary Contact…Secondary ContactMechanisms that can prevent gene flow when reproductively isolated species come back in contact with each other following isolation and divergence: - Prezygotic mechanisms make it very unlikely that interbreeding will even take place- Postzygotic mechanisms cause hybrids to become sterile or to fail to develop properly.- Outcomes1. Populations fuse and gene flow erases differences - no new species2. Populations are different and hybrids do not survive or reproduce - new species3. Hybrid zones form. Hybrids survive and reproduceSympatric- Intrinsic barrier blocks gene flow- Ranges overlap- Sympatric speciation occurs in populations that occupy the same geographic area. - Sympatric speciation is relatively common and quick to occur.PolyploidyA type of mutation, can also cause sympatric speciation. Definition: more than 2n chromosomes- Gametes not reduced to n during meiosis- Self-fertilization- Tetraploid (4n chromosome number)LECTURE QUESTION When will the biological species concept NOT work?- When species are sympatric- When species are nearly indistinguishable in morphology- When species are reproductively isolated- When species are exclusively asexualReview- Speciation is the outcome of isolation and divergence KEY- Species are distinct types of organisms that represent evolutionarily independent groups.- Lack of gene flow makes a species independent. - Modes of Speciationo Allopatric - geographic barrier blocks gene flowo Sympatric - intrinsic barrier blocks gene