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Carson - Parapatric Model of speciation Ranges of two...

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Carson's view: two "parts" to the genome: the " open variability system" and the " closed variability system" Open system has much variability , responds rapidly to selection (loci encoding allozyme polymorphisms such as enzymes in glycolysis and Krebs cycle, etc.); closed system is resistant to selection; less variable ) loci encoding courtship song, developmental patterns, etc . ) In Carson's view the closed system is reorganized during the flush-crash cycles, leads to a genetic change that contributes to reproductive isolation/mate recognition. Questions about the founder flush speciation: how small is population after crash?, how long does population stay at reduced population size? Could retain a large portion of the genetic variation after one crash; extended bottle necks will be more effective in reducing variation. These questions also could apply to Mayr's peripatric speciation model
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Unformatted text preview: Parapatric Model of speciation. Ranges of two differentiated forms are contiguous and non-overlapping. Patterns of discontinuities between differentiated forms/populations may be due to secondary contact after a period in allopatry, or the discontinuity could be due to primary differentiation in situ . One cause of this might be a steep environmental gradient or habitat boundary (see fig. 16.3 pg. 428). With selection on loci that affect reproductive isolation/mate recognition, populations can become differentiated. Will be apparent in the formation of a cline . Can lead to sufficient divergence of reproductive/mating characteristics that barrier to gene flow is established (e.g., plants growing on mine tailings have diverged in flowering time )....
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