Bio 203-001 Chapter 14 Notes
Bio 203-001 Chapter 14 Notes BI 203-001
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This 4 page Class Notes was uploaded by Jaime Jackson on Thursday April 7, 2016. The Class Notes belongs to BI 203-001 at Portland State University taught by Radhika Reddy in Winter 2016. Since its upload, it has received 39 views. For similar materials see in Biology at Portland State University.
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Date Created: 04/07/16
Thursday, April 7, y Chapter 14: The Origin of Species Objectives - Defining a species - Maintenance of Reproductive Isolation Formation of new species - - Extinction What Is a Species? - A species: potentially interbreeding natural populations which are reproductively isolated from other groups ” - The biological species concept : reproductive isolation of group ensures evolutionary independence - Each species follows a separate evolutionary path because alleles rarely move between the gene pools of different species Appearance can be misleading! - Similar appearance, different species Cordilleran flycatcher & Pacific slope flycatcher - - Anopheles dirus (carries malaria) and Anopheles harrisoni - Different Appearance, Same Species Northwestern garter snakes could be brown, black, gray, green, or - some shade in between How Is Reproductive Isolation Between Species Maintained? - Isolating mechanisms: Traits that prevent interbreeding Isolating mechanisms prevent offspring that are unfit or sterile - Premating isolating mechanisms: Geographical isolation - Geographical isolation prevents interbreeding between populations that do not come into contact because they live in different, physically separated places. - Ex: North rim vs. south rim of grand canyon Premating isolating mechanisms: Ecological isolation - Ecological isolationoccurs when species do not mate because they occupy different habitats. Example: each species of fig wasp breeds in the fruit of a different - species of fig Premating isolating mechanisms: Temporal isolation - Temporal isolation (time-based isolation) prevents breeding between two species occupying the same habitat because of different breeding season. - Example: Bishop pine pollination occurs in summer, Monterey pine pollination occurs in early spring Premating isolating mechanisms: Behavioral isolation 1 Thursday, April 7, y - Behavioral isolation is created by signals and behaviors that differ from species to species. - Example: The plumes and arresting pose of a courting male Raggiana bird of paradise are conspicuous indicators of this species Premating isolating mechanisms: Mechanical incompatibility - Mechanical incompatibility occurs when species cannot mate because their reproductive structures are incompatible - example: snails of species whose shells have left-handed spirals may be unable to copulate successfully with snails whose shells have right-handed spirals Postmating isolating mechanisms: Gametic incompatibility - Gametic incompatibility occurs when sperm from one species cannot fertilize eggs of another - Ex: fluids of the female reproductive tract may weaken or kill sperm of another species Red and purple sea urchin gametes don - ’t fuse because sperm cells contain a protein that allows them to bind only to eggs of their own species Postmating isolating mechanisms: hybrid inviability, hybrid infertility - Hybrid inviability:Cross-species fertilization occurs, but the resulting hybrid is unable to survive - Hybrid infertility:Hybrid unable to reprduce. Often caused by the failure of chromosomes to pair properly during meiosis, so eggs and sperm never develop - Example: Liger hybrids (a zoo-based cross between a male lion and a female tiger) Speciation: the process by which new species form - Isolation of populations: Species must remain isolated - If individuals move freely between two populations, interbreeding and the resulting gene flow will cause changes in one population to become widespread in the other - Genetic divergence of the populations must occur through the evolution of isolating mechanisms, driven by genetic drift or natural selection Evolutionary biologists group the different pathways to speciation into two broad categories - In allopatric speciation, the isolating mechanism is a physical barrier - In sympatric speciation, isolation occurs without geographical separation 2 Thursday, April 7, y Geographic separation of a population can lead to allopatric speciation Allopatric speciation: - Genetic divergence because of natural selection and genetic drift, lack of gene flow - Geographic isolation followed by allopatric speciation has been the most common source of new species Separation via: colonization of remote habitats (islands or reefs), - geological changes (volcanoes, earthquakes, continental drift) - Sympatric speciation: Genetic isolation without geographic separation - Ecological isolation (same region, different habitat) can reduce gene flow to the point of speciation Rhagoletis - is a parasite of the American hawthorn tree which is splitting into two species: one that breeds on apples and one that breeds on hawthorns - The two types of flies emerge with timing appropriate for their chosen host fruit and have very little chance of meeting The history of life can be represented by an evolutionary tree - The base of the evolutionary tree of life represents Earth ’s earliest organisms, ending with branches representing today’s species - Hypotheses and discoveries about the evolutionary relationships among species are often communicated by depictions of a portion of lif’s evolutionary tree Adaptive radiation is the rise of many new species over a relatively short period of time This process occurs when populations of one species invade a variety - of new habitats with few competitors - Tarweed plant colonization of the Hawaiian Islands resulted in 30 species Questions 1. Which of the following is a species? A. A group of interbreeding individuals that is reproductively isolated from other groups B. A group of organisms and their interactions with the environment C. The biotic and abiotic components of an ecosystem D. An individual organism and its niche 2. On the basis of differences in DNA and structure, West African elephants are thought to be a different species from Central, East, and South African savanna elephants and Central African forest elephants. Which isolation mechanism has occurred? A. Geographical isolation B. Ecological isolation 3 Thursday, April 7, y C. Temporal isolation D. Behavioral isolation 3. A female cricket does not understand the mating call of a male cricket. Which isolation mechanism is occurring? A. Geographical isolation B. Ecological isolation C. Temporal isolation D. Behavioral isolation 4. Sea urchins spawn their gametes freely into the surrounding ocean waters. The sperm of one type of urchin will not fertilize the egg of another type of urchin. Which isolation mechanism is occurring? A. Geographical isolation B. Ecological isolation C. Temporal isolation D. Gametic incompatibility 5. A leopard frog and a wood frog mate and produce offspring, which die within a few days. Which isolation mechanism has occurred? A. Geographical isolation B. Ecological isolation C. Hybrid inviability D. Hybrid infertility 6. Two populations of the columbine flower had lived at different altitudes in the same area. When the two were reunited, they could no longer breed. Which isolation mechanism has occurred? A. Geographical isolation B. Ecological isolation C. Temporal isolation D. Behavioral isolation 4
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