• DOI:10.1111/j.1558-5646.1978.tb04589.x
• Corpus ID: 30943286

THE FOUNDER‐FLUSH SPECIATION THEORY: AN EXPERIMENTAL APPROACH

@article{Powell1978THEFS,
  title={THE FOUNDER‐FLUSH SPECIATION THEORY: AN EXPERIMENTAL APPROACH},
  author={Jeffrey R. Powell},
  journal={Evolution},
  year={1978},
  volume={32}
}

• J. Powell
• Published 1 September 1978
• Biology
• Evolution

Stemming from Mayr's (1942; 1954) concept of the "founder principle", Carson (1968; 1971; 1973; 1975) hasdeveloped a somewhat unorthodox theory of speciation. Briefly, Carson views the steps in species formation as follows. A population undergoes a rapid expansion ("flush") due to temporarily permissive conditions or sudden genotype changes due to migrants or newly arisen variants. This newly expanded population colonzies areas previously unoccupied by the species. Many of the newly colonized areas are reached by only a few individuals or even a single gravid female; thus these new populations would exhibit founder effects. If one (or more) of these propagules colonizes a habitat suitable for the long term survival of the species it may undergo another flush due to reduced intraspecific competition. If, as is likely, the sudden flush causes the population to exceed the carrying capacity of the newly colonized environment, a population crash will ensue. If the population survives the crash, it may undergo a second flush stemming from the few survivors. Thus the new colony may undergo several flush-crash cycles before coming to a kind of equilibrium with the environment. At each crash the bottleneck populati n is small and genetic drift is strong. Carson argues that this new colony may now have undergone a "genetic revolution" of a magnitude which produces reproductive isolation with the progenitor population. The causes of the genetic change are two. First, the founder event and bottlenecks cause strong genetic drift effects. More importantly in Carson's view, the periods of population flush are times of relaxed selection. New genotypes, produced primarily by recombination, which were not fit enough to survive in the original population may survive during this relatively benign period. Thus the tightly integrated gene pool of the original population may become completely perturbed and then reorganized by selection acting on new arrays of previously untried genotypes. The main aspect of unorthodoxy of this theory is that unlike "classical" models of speciation (e.g. Dobzhansky, 1940; Mayr, 1963) reproductive isolation is not selected for; rather it comes about as a by-product of the genetic changes due to founder events and the flush-crash cycles. Carson postulates that adaptive divergence in the new environment is to a large degree