Lecture 23 _March 7_ Speciation post

Lecture 23 _March 7_ Speciation post - 2/25/11 Biology 171...

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2/25/11 1 Lecture 23: Monday March 7, 2011 Biology 171 Announcements Text Reading Chapter 26 (458-471) Types of evolutionary change The species concept Reproductive isolation Allopatric & sympatric speciation Adaptive radiation This Week in Discussion: Computer simulations of HWE and deviations from HWE Why We Care • How can we study biology without understanding where species come from? • The history of our planet is tied to the evolutionary history of life • It is in the nature of humankind to question our origins and our place in the universe The Unity of Life Explained By The Origin Of Species Through Evolution By Natural Selection Some Definitions Microevolution – small evolutionary changes that occur within populations of species – eg changes in beak size of Geospiza fortis Speciation – the formation of distinct species by accumulated genetic change Adaptive Radiation – the evolution of many diversely adapted species from a single common ancestor Macroevolution – substantive changes in biological design that occur over long periods of evolution
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2/25/11 2 Anagenesis vs Cladogenesis Anagenesis is a gradual change in form within a single species of organism Cladogenesis is branching evolution in which a common ancestor gives rise to novel species Only cladogenesis results in speciation and an increase in biological diversity The Biological Species Concept • Species are defined in a variety of ways by different scientists • The most common species concept is the biological species concept • It emphasizes reproductive isolation • Under this concept, distinct species are those that, if they meet, are unable to mate to produce fertile offspring Reproductive Isolation • Reproductive isolation is determined by one or more barriers to successful breeding • Prezygotic barriers – anything that prevent a sperm cell fertilizing an ovum • Postzygotic barriers – prevent the successful development of a zygote to a fertile adult Prezygotic Barriers • Prezygotic barriers impede mating or hinder fertilization if mating does occur • Habitat isolation • Temporal isolation • Behavioral isolation • Mechanical isolation • Gametic isolation
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2/25/11 3 These two species of garter snake are reproductively isolated in part because they live in different habitats (terrestrial vs aquatic) These two species of skunk are reproductively isolated in part because they breed at different times of year Courtship displays (behavior) unique to a species can act as prezygotic barriers to mating Blue-footed Boobies These two species of Mimulus are morphologically (mechanically) different so that they can’t be cross- pollinated
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2/25/11 4 Prezygotic Reproductive Barriers: Mechanical Isolation
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Lecture 23 _March 7_ Speciation post - 2/25/11 Biology 171...

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