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Macroevolution Speciation • The formation of new species • Species: A group of individuals capable of interbreeding • Populations are isolated, then there are changes in allele frequencies. The populations diverge and over time they can become distinct species. Reproductive Isolation • Prezygotic Isolation - when individuals of different species are prevented from mating • Allopatric Speciation • Habitat Isolation – geographic barrier • Sympatric Speciation • • • • Behavioral Isolation – little or no sexual attraction Temporal Isolation – mating/flowering occurs at different times Mechanical Isolation – structural differences in genitalia or flowers prevent gamete transfer Gametic Isolation – female and male gametes fail to attract each other/inviable DISPERSAL AND COLONIZATION CAN ISOLATE POPULATIONS. Island Continent 1. Start with one continuous 2. Island population begins 3. Finish with two populations population. Then, colonists float to an island on a raft. to diverge due to drift and selection. isolated from one another. VICARIANCE CAN ISOLATE POPULATIONS. River 1. Start with one continuous 2. Isolated populations begin 3. Finish with two populations population. Then a chance event occurs that changes the landscape (river changes course.) to diverge due to drift and selection. isolated from one another. Adaptive Radiation • Rapid evolution of many species from single common ancestor • Diverse geographical or ecological conditions Reproductive Isolation • Postzygotic Isolation - when individuals from different populations do mate, but the hybrid offspring produced have low fitness • Hybrid Inviability – zygotes fail to develop • Hybrid Sterility – fail to produce functional gametes • Hybrid Breakdown – offspring of hybrids have reduced viability of fertility • Tigon – Male tiger – Female lion • Liger – Male lion – Female tiger • Litigon – Male lion – Female Tigon – RARE! • Only exist in captivity (some are zoo mistakes from not keeping species separate) • Subspecies are populations that live in discrete geographic areas and have their own identifying traits but are not distinct enough to be considered a separate species •Soapberry bugs feed and mate on certain host plants including the soapberry tree. They began to feed on new species of plants that were introduced to their environment. These plants had fruits much smaller than those of the native plant species. Feeding on the fruit of a native species Feeding on the fruit of a nonnative species Nonnative fruits are much smaller than native fruits. Nonnative plant (small fruit) Native plant (large fruit) Evidence for disruptive selection on beak length Short-beaked population growing on nonnative plants Long-beaked population growing on native plants • Possible outcomes of secondary contact between two related populations: – – – – – Fusion of the populations Reinforcement of divergence Founding of stable hybrid zones Extinction of one population Origination of a new species Reinforcement of reproductive isolation (sympatric) of rhinocerous beetles (Laos) Polyploidy • a species may originate from accident during division resulting in extra set of chromosomes •Can lead to sympatric speciation • Autopolyploid – Parents of same species produce offspring with a doubling of chromosome number due to nondisjunction • Allopolyploidy - Parents that belong to different species produce offspring in which chromosome number doubles Autopolyploidy Allopolyploidy Allopolyploidy may occur after two species hybridize. Many diploid plant species have closely related polyploid species, supporting the claim that speciation by polyploidy is important in plants. In summary, speciation by polyploidization is driven by chromosome-level mutations and occurs in sympatry. Species 2 Species 1 Meiosis Haploid gametes Fertilization These chromosomes do not synapse and separate normally Error in meiosis or mitosis Allopolyploid cell—now each chromosome has a homolog Meiosis Diploid gametes (can fuse to form a tetraploid individual) Macroevolution • Microevolution - how populations of organisms change from generation to generation and how new species originate • Ex: a change in a species’ coloring or size • Macroevolution - the pattern of changes over broad periods of time Theories on how to interpret fossil record: Phyletic Gradualism – gradual accumulation of small changes; states fossil record is incomplete Punctuated Equilibrium – long periods of stability followed by short periods of rapid evolution; explains why few intermediate fossils are found The Oparin-Haldane Theory • In the early Earth, simple organic molecules were able to form only because oxygen was absent. • Presence of CO, CO2, H2, N2, H2O, S, HCl, HCN • Abiotic synthesis of organic monomers • Impossible now with an oxygen-rich atmosphere due to photosynthesis The Miller and Urey Experiment Reaction: – Heated “sea” – Made an “atmosphere” – Made “lightning” (electric sparks) in atmosphere – Cooled the atmosphere, creating “rain” with dissolved compounds • When analyzed, Miller and Urey found all 20 amino acids, several sugars, lipids, purines and pyrimidines of DNA and RNA, and ATP The Origin of Life Formation of: 1. Earth and atmosphere (hot gasses, little/no oxygen) 2. Seas (cooling Earth – gasses condensed) 3. Organic monomers (“organic soup”) • Energy from UV, lightning, etc. • See Oparin-Haldane Theory & Miller-Urey experiment 4. Polymers and self-replicating molecules (proteinoids) 5. Protobionts • 6. Precursors to cells; membrane-bound, unable to reproduce Primitive heterotrophic prokaryotes • Competition for resources increased; natural selection favored those more successful at obtaining food (from “soup”) • 3.5 billion years ago 7. Primitive autotrophic prokaryotes • 8. Photosynthesis ability from mutation Oxygen and ozone layer (from photosynthesis) • 9. As UV light is prevented from reaching surface, decreased abiotic synthesis of organic molecules Eukaryotes • 2.1 billion years ago • See Endosymbiosis Hypothesis Characteristics Of The Earliest Organisms • Prokaryotic • Small (surface to volume ratio) • Unicellular • Heterotrophic • Asexual reproduction • Organic monomers • Anaerobic • Aquatic • ATP • DNA or RNA • mRNA for information transfer • tRNA to carry amino acids • Ability to mutate • Ability to synthesize proteins Endosymbiotic Theory • Origin of Eukaryotes – – Explains larger, more complex cells with endomembranes Mitochondria and chloroplasts are similar to some bacteria – – – – • Similar size Own circular DNA with similar gene sequences Reproduce independently Double membranes (much like a vesicle after endocytosis) “A cell living within a cell” – mutualism