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Lecture/ Chapter 8 Study Notes

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University of Toronto St. George
Benjamin Wright

Lecture 8 Speciation Required readings: Evolution: A lizards tale (textbook) Key Concepts Terms: Polyploidy Taxonomic and biological species Hybridization Allopatric and sympatric speciation Autopolyploidy Adaptive radiation Allopolyploidy 1) The major issues: Species concepts, Modes of speciation 2) Adaptive radiation of plants and animals on islands 3) Hybridization and Polyploidy: Types of polyploidy, Evolutionary significance Number One: Since populations of a species frequently become adapted to different local environments, it is not unexpected that some will diverge to the point of being unable to interbreed. If this is the case, the process of speciation has occurred. What types of biological changes are necessary for the establishment of a new species? Do the changes that result in a new species occur quickly and result from a few genes? Are speciation mechanisms different between plants and animals? Although simple answers are tempting, such questions are difficult to answer explicitly. In fact, it is doubtful that simple answers exist since new species may become established via several avenues. The factors important in a particular situation are likely to depend upon the characteristics of the organism, the environment, and the genetic variation available for selection. The term species refers to both a taxonomic category and a biological concept. Taxonomic species are usually based on distinct morphological differences. In most animals, taxonomic species are in general equivalent to biological species where biological species are defined as: groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups However, in certain plants the two concepts are frequently not equivalent, because taxonomic species are frequently interfertile, despite clear morphological differences between them. This pattern is particularly well developed in island groups, where rapid adaptive radiation results in striking morphological and ecological differentiation between species, without strong genetic divergence. This situation has led some
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