01-outline - BIOL 1010 FW 0809 Chapters 24 & 25...

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BIOL 1010 FW 0809 Speciation, History of Life Chapters 24 & 25 Speciation (ch. 24) bridges microevolution and macroevolution What is a species? Biological Species Concept (BSC) A species is a population or group of populations whose members have the potential to interbreed with one another to produce viable, fertile offspring. - BSC emphasizes divergence arising from reproductive isolation, as interbreeding would result in gene flow between two groups, reducing genetic divergence Reproductive isolation Æ genetic divergence Æ speciation - barriers to reproduction: pre-zygotic, post-zygotic - prezygotic isolating mechanisms can be: Habitat isolation (e.g. aquatic vs terrestrial), Temporal isolation (e.g. mating in spring vs mating in fall), Behavioural isolation (e.g. recognizing or attracting mates vs courtship displays), Mechanical isolation (e.g. the “mechanics” of copulation and successful fertilization are not compatible between two different species), Gametic isolation (e.g. egg of one species doesn’t allow fertilization by sperm of another species) - postzygotic isolating mechanisms can be reduced hydrid viability (hybrids are weaker or not competitive against non-hybrids), reduced hybrid fertility (e.g. donkey x horse produces sterile mule), hybrid breakdown (hybrid F1’s breed and produce unviable F2’s) - BSC inapplicable to fossils, asexually reproducing organisms Morphological Species Concept - a set of organisms sharing a unique suite of physical characteristics Phylogenetic Species Concept - a set of organisms with a unique evolutionary history - strongest phylogenies use multiple independent lines of evidence Speciation - allopatric (“different country”) speciation – geographic barrier - reproductive isolation arising from chance alone (e.g. genetic drift), natural selection of adaptive traits e.g. case example of fruit flies on different sugar media - sympatric (“same country”) speciation – no geographic barrier e.g. polyploidy e.g. case example of Rhagoletis fruit fly - geographic isolation itself does not generate speciation events, it facilitates them
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Reproductive isolation… via allopatry - doesn’t necessarily involve a reproductive isolating mechanism via sympatry - MUST first involve a reproductive isolating mechanism Gradual vs sudden speciation? (gradualism or punctuated equilibrium?) 1 MYr 0.1 MYr
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01-outline - BIOL 1010 FW 0809 Chapters 24 & 25...

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