Patterns predicted from the action of reinforcement

Patterns predicted from the action of reinforcement - which...

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Patterns predicted from the action of reinforcement: Selection in zone of overlap for increased premating isolation. See artificial demonstration with a selection experiment (fig. 16.4, pg. 432). Reinforcement model assumes that hybrids are less fit (=means by which selection for further isolation can operate). This assumes that post mating barriers arise first and that premating barriers arise as a result of selection in sympatry; these assumptions may not hold in all cases. However, if premating barriers evolved first, there might be little hybridization (speciation complete?); if there was no postmating barrier, even with small amounts of hybridization the two forms would fuse back together because there would be no selection against hybrids! Reinforcement is actually a special case of character displacement
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Unformatted text preview: which is the accentuation of differences between species (or forms) by selection against the individuals of similar phenotype (reinforcement = reproductive character displacement and is achieved by selection against hybrids). If reinforcement is true, we should expect to see displacement of characters associated with pre-mating barriers to gene exchange in areas of secondary contact. Some cases we do: calling songs of anurans ; Frequently such reproductive character displacement is not observed . When "reinforcement-like" patterns are observed, one has to be sure that the phenotypic shift is actually an evolutionary response to the presence of the other incipient species and not to some other clinal variation (e.g., ecological factors that generate parallel clines)....
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