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Lec08.species - Speciation Importance The chief process by...

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1 Speciation ± Importance : ± The chief process by which life’s diversity has been generated “When on board H.M.S. Beagle as naturalist, I was much struck with certain facts in the distribution of the organic beings inhabiting South America, and in the geological relations of the present to the past inhabitants of that continent. These facts … seemed to throw some light on the origin of species- that mystery of mysteries, as it has been called by one of our greatest philosophers.” -Charles Darwin- Speciation ± Goals ± Understand what we mean by a species ( species concepts ) ± Look at the processes by which new species can be generated ( modes of speciation ) ± Look at the evidence for speciation by two modes ± Things do seem to fall into categories ± But how do we decide when two organisms should be in the same species or in separate species ± Originally, folks attempted to do this purely by appearance (phenetics), which led to endless squabbling about what should really be a species. ± Lumpers and splitters
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2 The Problem with Phenetics ± Measure as many traits as possible, on multiple organisms ± Use cluster statistics to distinguish one species from another Biological questions left unaddressed by a phenetical approach ± How different does one individual have to be from another before they should be called different names? ± Why do members of the same species look similar?? ± Can we define species in a biologically relevant way that isn’t arbitrary? Species Concept #1 ± Biological Species Concept (BSC): a species is an interbreeding group of organisms that is reproductively isolated from other organisms (Ernst Mayr, also Dobzhansky and Huxley) ± Rooted in a population genetic perspective ± The sharing of a common gene pool binds the members of the species together ± Members of a species look similar because they are interbreeding ± Have to have developmental programs that are similar enough for viability to be maintained
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Reproductive isolating mechanisms ± Prezygotic/Premating ± Geological (Separated by large distances, e.g., oceans) ± Ecological (living in different places in the same community) ± Temporal (seasonal; diurnal) ± Ethological (behavior) ± Different pollinators (behavior?) ± Gametic isolation (external and internal fertilization) ± Postzygotic/Postmating ± Hybrid inviability (hybrids die during development) ± Hybrid sterility (e.g., a mule) ± Hybrid breakdown (too complicated for this slide!) Hybrid Breakdown Example Species 1 Species 2 F 1 F 2 ± The different types of isolation are not mutually
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Lec08.species - Speciation Importance The chief process by...

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