EBIO 1220 1st Edition Lecture 4Outline of Last Lecture I. Speciationa. What is a Species?II. Species Conceptsa. Biological Species Conceptb. Morphological Species Conceptc. Ecological Species Conceptd. Phylogenetic Species ConceptIII. Barriers to Gene Exchangea. Reproductive Isolationb. Barriers to Gene Flowc. Results of Reproductive IsolationOutline of Current Lecture II. Isolationa. Reproductive Isolationb. When Populations Come Back TogetherIII. Pre-Zygotic Isolating MechanismsIV. Post-Zygotic Isolating MechanismsV. Allopatric vs. Sympiatric IsolationVI. Evolutionary History of LifeCurrent LectureII. Isolationa. Reproductive Isolationi. Existence of biological factors (barriers) that impede 2 groups from producing viable, fertile offspringb. When Populations Come Back TogetherThese 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. Reinforcement: the two populations can no longer interbreed, hybrids arenot viable and the two become separate species, 2 species totalii. Fusion: the two populations readily interbreed and fuse back into the same species, 1 species totaliii. Stability: hybrids are viable and fertile and become their own separate species, 3 species totaliv. Hybrid: offspring of cross b/w different speciesIII. Pre-Zygotic Isolating Mechanismsa. Inhibit mating between two species before an egg can be fertilizedb. Temporal: Closely related populations find mates at different times of the yearc. Behavioral: Closely related populations use different mating ritualsd. Mechanical: Closely related populations try to mate but it doesn’t worke. Gametic: Cell surface proteins on eggs don’t respond to sperm from a closely related population and a zygote is not formedIV. Post-Zygotic Isolating Mechanismsa. Inhibit mating between two species after fertilizationb. Reduced Hybrid Viability: offspring are only viable for a few days at most and are sicklyc. Reduced Hybrid Fertility: hybrids are viable but sterile and the hybrid population does not lastd. Hybrid Breakdown: offspring are viable and fertile in the first generation but overtime the become inviable and/or infertileV. Allopatric vs. SympiatricSpeciationa. Allopatric: new species is formed due to geographic isolationi. No gene flow b/w closely related populationsii. The two populations evolve independently: mutation, selection, genetic driftiii. Definition of barrier depends on the ability of a population to disperseb. Sympiatric:new species forms w/o geographic separationi. Rareii. Takes place in geographically overlapping populationsiii. Can result from…1. The appearance of new ecological niches2. Different mate-selection preferencesiv. Example: Cichlids live in the same waters but have evolved separately VI. Evolutionary History of Lifea. Earth is 4.6 billion years oldb. Major biological milestones over the past 3.8 billion yearsc. Geological events change the course of evolutiond. Life changes the planet it inhabitse. Continental Drifti. Pangea current postion of continents  continuingii. Geographic isolationiii. Geological differencesiv. Climate