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Lecture 20

Lecture 20

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James Thomson

Lecture 20 Two main species concept - Taxonomic or morphological o Based primarly on distinct morphological differences o What the things look like o Commonly used o Can be arbitrary though o Collect species and identify gaps in phenotypic variation o Criticized by geneticists, because different people will come up with different numbers - Biological o Based on inter-fertility among individuals o A lot of organisms that you cannot cross o Have info only about those that we can o What about organisms that do not have sex, like bacteria o Found by Ernst Mayr – Harvard 1904-2005  A group od interbreeding natural populations that are reproductively o First idea was suggested by Dobzhansky Two main modes of speciation - Allopatric o Apart o Start with a population that gets split, geographical barrier that limits gene flow, evolution and genetic differentiation occurs; if they do come back together they cant interbreed o Geographical - Sympatric o Should be gene flow going on that stops diversion o Hardly occurs o Controversy: how you can differentiate it from allopatric? o Sympatric speciation occurs in plants, but rare in animals RI –reproductive isolation - Finding a compatible mate - Mating & fertilization - Development of zygote - Adult growth & survival - Reproduction & RI mechnisms - premating isolation o geography is different, or different habitats(ecology) o temporal, not the same time for mating; behavioral, female don’t choose you o mechanical, things just dont fit; prevention of fertilization occurs o apple maggot flies: habitat and temporal isolation; native to north America; use horthons as a host; population that subdivided in teo groups to different food resources; 6% matings between each other; example of sympatric speciation o Shemske; monkey flower: pollinator preferences & altitude; in the wild don’t mate together, but if you breed them by yourself they can mate - postmating isolation o individuals mate together but preventing the proper functioning of zygotes once they are formed o inviability, sterility, or abnormal
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