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November 29.doc

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McGill University
Biology (Sci)
BIOL 111

Bio 111 Alanna Houston November 29, 2007 UNDERSTANDING DIVERSIFICATION Species: - Species Concepts: ritualized ways of determining whether something is a species or not o Typological (morphological) – Is it distinctive enough by looking at it from everything else that I can separate it from other species? o Biological – whether or not individuals from the two potential species will interbreed with each other o Phylogenetic – Are they genetically different enough? - Is the diversity of skull morphologies found in dogs comparable to all carnivora? o Dogs show greater levels of diversity and explore new morphological space o - A typical perception of the biological species concept is that it doesn’t allow species to interbreed and produce viable offspring. o What is a liger not? Always infertile. Biological Species Concept: - Groups of actually or potentially interbreeding natural population which are reproductively isolated from other such groups - Hard to apply to things found in different places - The BSC allows for SOME gene flow between the two species - Problems: o Difficult for allopatric (different places) populations o Not particularly useful for fossils Speciation: Bio 111 Alanna Houston - A process: - Not an event - Mechanisms of Speciation: o Uniform Natural Selection – species in two separate places might be adapting to same environment but mutations may be different. When they come back together, the mutations may be incompatible o Divergent Natural Selection (ecological speciation) – species in two separate places adapting to different environments and when they come back together, they may not be compatible o Genetic Drift – genetic drift occurring in two separate places and then are incompatible o Polyploidy – 8n, 16n etc. Happens quickly in plants. Different numbers of chromosomes are not compatible with each other o Hybridization – formation of new species. Two things that are compatible can create hybrid lineage that cannot reproduce with either parent o Sexual Selection o Cytoplasmic incompatibility Ecological Speciation: - - Disruptive/divergent selection drives adaptive divergence - Reproductive isolation evolves as a consequence - Speciation in Darwin’s finches is presu
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