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Unformatted text preview: Speciation Speciation Today ’s questions: I. How do biologists recognize species? II. How does speciation occur? • Mechanisms of isolation • Mechanisms of divergence I. How do biologists recognize species? A species is a population or group of populations in which evolutionary forces are acting independently. Speciation is a splitting event: Species are genetically isolated from each other. New species are created by: 1. Genetic isolation 2. Genetic divergence Use of species concepts (species are easy to define and hard to identify) Biological species concept
Criterion for Advantages Disadvantages Identifying species Morphospecies concept
Criterion for Advantages Disadvantages Identifying species Phylogenetic species concept Monophyletic group (aka lineage, clade): an ancestor and ALL of its descendants Paraphyletic group: an ancestor and some, but not all, of its descendants “One‐snip test” for identifying monophyletic groups: An example of the phylogenetic species concept Asian elephants West African elephants East African elephants (Note: if individuals from different populations do not have unique traits, then there are no synapomorphies and the populations represent the same species.) II. How does speciation occur? A. Allopatric (“different land”) speciation If populations are separated geographically, then evolutionary forces will act on them independently. 1. Dispersal Kaui Oahu Molokai Maui Hawaii D. hemispiza D. differens D. planitibia D. silvestris D. heteroneura (Oahu) (Molokai) (Maui) (Hawaii) (Hawaii) b. Vicariance: splitting of an existing range into fragments e.g. Death Valley pupfish B. Sympatric (“same land”) speciation Can gene flow stop, or be reduced enough to start speciation, if populations are in the same geographic area? e.g. Mimulus lewisii and M. cardinalis 1. Mechanism of isolation: 2. Mechanism of divergence: e.g. Rhagoletis pomonella (apple and hawthorn flies) 1. Mechanism of isolation: 2. Mechanism of divergence: e.g. Tragopogon mirus 1. Mechanism of isolation: 2. Mechanism of divergence: Punchline: it is possible to study speciation (“macroevolution”) experimentally in the field and in the lab. ...
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