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Macroevolution Macroevolution is the study of major biological changes evident in the fossil record Includes the following: 1. Multiplication of species 2. Origin of structures like feathers and large brains 3. Diversification of species – like flowers 4. Mass extinctions that lead to explosions like the explosion of mammals after the dinosaurs became extinct speciation Speciation is the origin of new species Branching vs. non-branching Branching – a lineage is split into two or more species Non-branching – initial species becomes new species Anagenesis vs. Cladogenesis The Origin of Species Biological species concept – groups of interbreeding natural populations whose members ONLY breed with each other to create fertile offspring. What keeps members of different species apart? Reproductive Barriers Prezygotic barriers – occur before conception Post-zygotic barriers – occurs after conception Pre-zygotic Barriers Temporal Isolation – mating or flowering occur at different time of the year/day Ex. Western spotted skunks breed in fall, while eastern spotted skunks breed in the late winter Habitat Isolation – species living in the same region may occupy different habitats Ex. Some Garter snakes live in water/some on land Behavioral Isolation-courtship rituals are very specific Ex. Birds Mechanical isolation-structural differences in genitalia or flowers prevent copulation or pollen transfer Ex. Insects and flowers Gametic isolationmale sperm cannot fertilize the egg Post-zygotic Barriers Hybrid Inviability – hybrid zygotes fail to develop or reach sexual maturity Hybrid Sterility – Hybrid individuals fail to produce young Speciation When a population is somehow severed from the parent population and over time its gene pool is altered. Allopatric and sympatric Allopatric speciation Isolation is the result of a geographic barrier Ex. Galapagos finches True speciation only occurs if the remaining populations will NOT breed allopatric Sympatric When a sub-population arises in the midst of the parent population Many plant species have accidental polyploidy in meiosis. They produce zygotes with multiple sets of chromosomes. They can no longer reproduce with parental generation. Evolution of Wheat What is the tempo of speciation? Gradual vs. punctuated Punctuated equilibrium model – species most often diverge in spurts of rapid change instead of slow and gradually. Over a few to ten thousand years, genetic drift and natural selection can change small, isolated species Punctuated Equilibrium Archaeopteryx Exaptation Term used to describe a structure that evolves in one context, but becomes adapted for another. However, natural selection cannot anticipate future need Ex. Light bones in reptiles Evo-Devo How do evolution and development interface? Genes control the development of an organism from zygote to adult Turning these genes on and off at certain times can have a profound effect on development. Paedomorphosis – the retention of juvenile features as an adult Ex. axototl Axototl Chimpanzee vs. human skulls We retain a skull more like that of our fetal skull History of biological diversity Macroevolution is tied to the history of the Earth Fossils are recovered from various sources Sedimentary rocks Skulls Petrified trees Tracks Body parts Amber Geological Time Scale Four eras – Precambrian, Paleozoic, Mesozoic, Cenozoic Fossils are dated by carbon dating Handout At the end of the paleozoic era (250mya), Pangaea was formed. The formation of pangaea reduced coastline and changed the environment for many terrestrial species. Changing ocean currents killed many marine species Breaking of Pangaea 180 MYA during the mesozoic Caused major geographic isolation Continental drift Patterns of Evolution Divergent evolution – when two isolated population evolve independently (Ex. Brown and polar bears) Adaptive radiation – rapid evolution of a variety of species from a single ancestor (ex. Darwin’s finches) Convergent Evolution – when two organisms without a common ancestor occupy the same niche, so they have the same characteristics. (ex. Porpoise and penguin) Patterns cont. Parallel Evolution – two related species who have made similar evolutionary changes. Ex. Placental and marsupial wolf Co-evolution – predator/prey relationships Adaptive Radiation
