Modes of speciation and inferences based on genetic distances

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In order to utilize molecular, cytogenetic and other population genetic data to test hypotheses concerning speciation mechanisms, it is necessary to have a mechanistic taxonomy of speciation. Current theories of speciation tend to be explanatory but not predictive, and the lack of a mechanistic classification of modes of speciation is a great hindrance to developing predictive theories. A tentative mechanistic taxonomy is proposed in which speciation mechanisms are subdivided into two major categories: transilience modes and divergence modes. In transilience modes, the evolution of isolating barriers depends upon a genetic discontinuity characterized by extreme instability of the intermediate stages. The pattern or mechanism of inheritance itself induces this instability. This nature of the discontinuity also implies that natural selection alone cannot induce a transilience; rather, the transilience is characterized by overcoming some selective barrier. Hence, the primary driving force of a transilience is the interaction of selection with other strong evolutionary forces and genetic constraints - such as founder events interacting with strongly epistatic polygenic systems, extreme inbreeding and drift overcoming strong underdominance, or hybridization followed either by selection for hybrid maintenance or by recombination coupled with some sort of hybrid dysgenic phenomenon. Under divergence, the isolating barriers evolve in a continuous fashion with some type of natural selection being the primary driving force - such as selection independently operating in extrinsically isolated subpopulations, selection on a geographic cline with isolation by distance, or selection over diverse habitats in the absence of isolation by distance. This mechanistic taxonomy is used to generate expectations concerning genetic distances.

Original languageEnglish
Pages (from-to)719-729
Number of pages11
Issue number4
StatePublished - 1980
Externally publishedYes

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Genetics
  • General Agricultural and Biological Sciences


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