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Origin of Species • How do we define species? • A population of organisms that produces viable fertile offspring in nature. • When does this definition fall apart? • Asexual,extinct and blurred organisms • What definition is used in these cases? • Morphospecies concepts • What is the main distinction that must occur for the origin and integrity of distinct species? • Reproductive isolation • Which sort of reproductive isolation mechanism is at work in the following examples? • Firefly signals with specific flashes to attract mates • male dragonfly has appendages that clasps female during mating • brown trout breed in the fall and rainbow trout in the spring • 1 type of garter snakes lives in the water and the other lives on land • Horse and donkey produce sterile mule • frogs that mate and produce offspring that do not quite develop Biogeography of Speciation • What is the difference between allopatric and sympatric speciation? • Allopatric speciation involves a geographical barrier between 2 groups • Sympatric speciation is the result of a genetic isolation without a geographical barrier Conditions for Allopatry • Peripheral isolate where the fringe organisms are already somewhat different from mainstream population • Genetic drift can occur to a small peripheral isolate • The genetic drift continues to change gene pool until the group is large • Natural selection will select the best fit traits among the new group to survive Ring Species: Allopatric Speciation in Progress Adaptive Radiation • Islands are laboratories of speciation • Adaptive radiation is the evolution a number of different new species from a common ancestor • Archipelago's are the home of adaptive radiations What sort of reproductive barrier is this? Prezygotic Has reproductive isolation occurred? Sympatric Speciation • Genetic alterations result in a reproductive barrier • Can occur in a single generation • More frequently seen in plants • Nondisjunction and selfing leads to polyploidy • autopolyploid • alloployploid • Evolution of wheat Sympatric Speciation in Animals Under normal light Under monochromatic light Genetic Mechanisms of Speciation • Adaptive Divergence: • reproductive barriers evolve as secondary result of divergence • the barriers evolve to enhance reproduction within the group not to eliminate reproduction between groups • reproductive barriers occur as a side effect of the accumulated adaptive divergences Tempo of Speciation • Gradualism • Punctuated Equilibrium From Speciation to Macroevolution • Speciation is the boundary between micro and macroevolution • Cumulative change over vast amounts of time accounts for macroevoulution • How do evolutionary novelties evolve? … Eye Evolution Origin of Novelties • How do large scale novelties arise? • Exaptation = modifications of older structures – Panda’s thumb stinger of bees etc… • Genetic changes that lead to devlopmental changes: – Allometric growth - relative rates of growth differs, change one stage and see big change – Alter timing of developmental events, such as sexually active juveniles – Alteration in homeotic genes • Evolution, however, is not goal oriented • Tetrapod evolution – Fish; Hox gene leads to fin development – Chicken; same Hox gene leads to leg development